OF THK
UNIVERSITY
-J
DR. WILLIAM KONRAD ROENTGEN, pp. 69 to 85.
Born in Holland, 1845.
From a photograph by Hanfstaengl, Frankfort-on-the-Main.
ROENTGEN RAYS
AND
PHENOMENA .
OF THE'"'
ANODE AND C A T H 6 D E
PRINCIPLES, APPLICA TIONS AND THEORIES
BY
EDWARD P. THOMPSON, M.E., E.E,
Mem. Amer. Inst. Elec. Eng.
Mem. Amer. Soc. Mech. Eng.
Author of "Inventing as a Science and an Art."
CONCLUDING CHAPTER
BY
PROF. WILLIAM A. ANTHONY,
Formerly of Cornell University.
Past President Amer. Inst. Elec Eng.
Author, with Prof. Bracket! of Princeton, of "Text-Book of Physics. 1 "
60 Diagrams. 45 Half-Tones.
NEW YORK :
D. VAN NOSTRAND COMPANY,
23 MURRAY AND 27 WARREN STREET.
T4-
Cooyright, tSge,
BY
EDWARD P. THOMPSON,
Temple Court Building, New York.
^t 7
PREFACE.
IN addition to the illustrated feature for exhibiting the nature
and practical application of X-rays, and for simplifying the descrip-
tions, the book involves the disclosure of the facts and principles,
relating to the phenomena occurring between and around charged
electrodes, separated by different gaseous media at various press-
ures. The specific aim is the treatment of the radiant energy
developed within and from a discharge tube, the only source of
X-rays.
Having always admired the plan adopted by German investi-
gators in publishing accounts of their experiments by means of
numbered paragraphs containing cross-references and sketches, the
author has likewise treated the investigations of a large number
of physicists. The cross-references are indicated by the section
sign (). By reference, the analogy, contrast, or suggestiveness may
be meditated upon. All knowledge of modern physics is based
upon experiments as the original source. Inasmuch as many years
may be expected to elapse before the innumerable peculiarities of
the electrial discharge will be reduced to a pure science, and also
in order that the contents of the book may be of value in the
future as well as at present, the characteristic experiments of
electricians and scientists are described, in general, by reference to
their object, the apparatus used, the result, the inferences of the
experimenter, and the observations of cotemporaneous or later
physicists, together with a presentation here and there of theoreti-
cal matters and allusion to practical applications.
The classes of reader to which the book is adapted may best be
known, of course, after perusal, but some advance intimation of the
kind that the author had in view may be desired. Let it be
known that, first, the student and those generally interested in sci-
11 PREFA CE.
ence ought to be able to comprehend the subject-matter, because
experiments are described, which are always the simplest means
(e. "., in a popular lecture) for explaining the wonders of any given
scientific principles or facts. Thus did Crookes, Tyndall, Thom-
son (both Kelvin and J. J.), Hertz, etc., disseminate knowledge by
describing their researches and reasoning thereon.
In view of the tremendous amount of experimenting which has
been carried on during the past few years in connection with the
electric discharge, it was difficult to determine just how far back to
begin (without starting at the very beginning), so that the student
and general reader, whose object is to become acquainted espe-
cially with the properties of cathode and X rays, might better under-
stand them. The author realized that it was necessary to go back
further and further in this department of science, and he could not
easily stop until he had reached certain investigations of Faraday,
Davy, Page, and others, which are briefly noticed in an introductory
sense. Take, for example, the inaction of the magnet upon X-rays
in open air. 79. Of course, it would be of interest for the stu-
dent to know about Lenard's investigations relating to the action
of the magnet upon cathode rays inside of the observing tube.
720. It would follow, further, that he would desire to know about
Crookes' experiment relating to the attraction of the magnet upon
cathode rays within the tube. 59. In order that he might not
infer that Crookes was the first to investigate the action of the mag-
net upon the discharge, it was evident that the book could be made
of greater value by relating the experiments of Prof. J. J. Thomson
as to the discharge across and along the lines of magnetic force,
31, and Pliicker's experiment on the action of the magnet upon
the cathode column of light. 30. The interest became in-
creased, instead of diminished, by noting De la Rive's experiment
on the rotation of the luminous effect of the discharge by means of
the magnet. 29. Being now quite impossible to stop, Davy's
electric arc and magnetic action upon the same had to be alluded
to, at least briefly. 28. On the other hand, the very earliest
experiments with the discharge in rarefied air are not described
occurring as remotely as the eighteenth century so ably treated of
in Park Benjamin's work. Those facts that have some mutual
PREFA CE. Ill
tearing are brought forward to serve as stepping-stones to the
investigation of cathode and X rays.
Secondly, the author often imagined that he was writing in
behalf of the surgeon and physician and those who intend to ex-
periment, especially when he found in his investigations of recent
publications descriptions in detail of the electrical apparatus em-
ployed in experimenting with X-rays. He improved the oppor-
tunity of repeating the statements of the difficulties, and how they
were overcome ; also, the precautions necessary to be taken, and,
besides, the kind of discharge tubes and apparatus best adapted for
particular kinds of experiments. The chapter on applications in
diagnosis and anatomy, etc., is of especial interest to physicians.
Thirdly, as the discovery of the Roentgen rays has established a
new department of photography, those who are interested in this art
may be benefited by the results and suggestions disclosed in con-
nection with photographic plates, time of exposure, adjuncts for
best results, precautions for obtaining sharp shadows, and steps of the
process, from beginning to end, for carrying on the operation.
Fourthly, expert physicists and electricians, professors, etc., need
something that the above classes do not, and this is the reason why
the author has not assumed the burden of carrying any line of
thought or theory from the beginning to the end of the treatise, nor
has he made the book in any way a personal matter by criticising
experiments, nor even by favoring the views of one over the other,
unless it is in an exceptional case here and there ; but in each in-
stance the investigator's name is given, and that of the publication
in which the account may be found, so that the scientist may refer
thereto to test the' correctness of the author's version of the matter,
or to learn the nature of the minute details and circumstances.
The author suggests that the study of the phenomena of the dis-
charge tube would not be amiss in scientific schools and colleges.
He argues that in view of all experimenters in this line having been
made enthusiastic and fascinated by reason of (i) the beautiful effects,
(2) the field being always open to new discoveries, (3) the direct
practical and theoretical bearing of the peculiar actions upon other
-departments of electricity, light, heat, and magnetism, (4) the pleas-
ure in attempting to obtain results reported by others, and espe-
IV PREFACE.
cially the large amount of valuable theoretical and practical instruc-
tion resulting therefrom, by repeating the experiments or studying
them, and (5) the possible applications of the discharge tube in con-
nection with electric lighting and in the new department of sciagra-
phy by X-rays, and for other good and valuable considerations it
follows that students who have been through or who are studying
a text-book of physics and electricity would be greatly benefited
by a course in the discharge-tube phenomena.
In view of the large amount of dictation necessary in order to
complete the work in such a short period, and in order that the sub-
ject-matter might involve the treatment of the latest work of the
French and German as well as of the English and American, and
inasmuch as the journals of the latter did not always contain com-
plete translations and, for better service in behalf of the readers, the
authorship was shared with others, and, therefore, much credit is
due to Prof. Anthony for final chapter, to Mr. Louis M. Pignolet for
assistance in connection with French periodicals and academy papers
( 630, 84, 99, IOKZ, 103^7, ii2#, 1240, 128, at end, 139^7, 154, 155,
156, 157, 158, and 159); to Mr. N. D. C. Hodges, formerly editor
and proprietor of Science, who obtained some pertinent accounts,
( 9T a > 97&> 99^> > C> D, to 99 T, inclusive) by investigations of
recent literature at the Astor Libary, New York ; and also to Mr.
Ludwig Gutmann (Member American Institute of Electical En-
gineers) for a few translations from the German.
Credit is given in each instance to all societies and publications
by naming them in the respective paragraphs herein. In nearly
every case the author prepared his material from original articles-
and papers contributed by the investigators to ' the societies or
periodicals.
The author has prepared himself to withstand, with about half
as much patience as he expects will be required, all criticisms based
upon disappointments which may be experienced by the true, or the
alleged true, first discoverer of any particular property of the electric
discharge not duly credited. He has been particular in present-
ing knowledge as to physical facts and principles, but not equally,
perhaps, as to the originator of the experiment, or as to the actual first
discoverer, for the simple reason that the book is in no sense a his-
PREFA CE. V
tory not a biography. Where the paragraph has been headed, for ex-
ample, " Svvinton's Experiment," it means that that party (accord-
ing to the article purporting to be written by him) made that
experiment. Some one else may have made exactly the same experi-
ment previously, yet the instruction is equally as valuable as though
the researches of the first discoverer had been related. On the other
hand, the author has never had any intention of giving credit to the
wrong party. The dates in the captions indicate the general chrono-
logical order in behalf of those thus interested. With this explana-
tion, it is thought that the claimants will be much more lenient in
their criticisms concerning priority of discovery. While the develop-
ments have generally followed each other historically, as well as ap-
propriately for the purpose of instruction, yet now and then it was
preferable to place the description of a comparatively recent experi-
ment in conjunction with some description of an experiment made
at a much earlier date. For this reason, also, the book is not of a
chronological nature. The subject-matter, as usual, is divided into
chapters, but the sections are to be considered as subordinate chap-
ters, having different shades of meaning, and the one not necessarily
bearing a direct relation to the contents of its neighbor, but as, in a
novel or a treatise on geometry, having its important part to play in
conjunction with some later or preceding section.
EDWARD P. THOMPSON.
TEMPLE COURT BUILDING, NEW YORK,
August, 1896.
CONTENTS.
^
CHAPTER I.
1. Secondary Current by Induction. No Increased E.M.F ..... FARADAY
2. Electric Spark and Increased E.M.F. by Induced Current ....... PAGE
3. Spark in Secondary Increased by Condenser in Primary ...... FIZEAU
4. Atmosphere around an Incandescent Live Wire .......... VINCINTINI
5. Magnetizing Radiations from an Electric Spark .............. HENRY
6. Arcing Metals at Low Voltage ............................ FARADAY
7. Non-arcing Metals at High Voltage. Practical Application. ..WuRTS
8. Duration of Spark Measured .......................... WHEATSTONE
Discharge Intermittent, Constant, and Oscillatory by Variation of
Resistance .......................................... FEDDERSEN
Musical Note by Discharge with Small Ball Electrodes. Invisible
Discharge ............................................. FARADAY
Pitch of Sound Changed by Approach of Conductor Connected to
Earth ..................................... FARADAY and MAYER
10. Brush Discharge. Color. Striae. Nitrogen Best Transmitter of a
Spark, and its Practical Bearing in Atmospheric Lightning.
Cathode Brushes in Different Gases .................... FARADAY
11. Glow by Discharge. Glow Changed to Spark. Motion of Air.
Apparent Continuous Discharge during Glow .......... FARADAY
12. Spark. Solids Perforated ................................... LULLIN
13. Spark. Glass Perforated. Holes Close Together. Practical Ap-
plication for Porous Glass ................................. FACE
14 and I4. Spark. Penetrating Power. Conducting Power of Gas.
Relation of E.M.F. to Pressure of Gases. Discharge through
Hydrogen Vacuum Continued with Less Current than that Re-
quired to Start it ......... KNOCHENHAUER, BOLTZMANN, THOMSON
(KELVIN), MAXWELL, VARLEY, HARRIS, and MASSON
Dust Particles or Rust on the Electrodes Hasten Discharge. .GORDON
Where the Distance is Greater, the Dielectric Strength is Smaller,
Both Distances Being Minute ................ THOMSON (KELVIN)
17. Discharge through Gases under Very High Pressures. Increased
Dielectric Strength ................................... CAILLITET
18. Discharges in Different Chemical Gases Variably Resisted. .FARADAY
19. Gas as a Conductor. Molecule for Molecule, its Conductivity Greater
than that for Gases .............................. THOMSON, J. J.
CO'N TENTS. VI I
20. Relation of Light to Electricity. The Square Root of the Dielectric
Capacity Equal to the Refractive Index.
BOLTZMANN, GlBSON, BARCLAY, HOPKINSON, and GLADSTONE
21. Hermetically Sealed Discharge Tubes with Platinum Leading-in
Wires PLUCKER and GEISSLER
22. Luminosity of Discharge Tubes Produced by Rubbing. Increased
by Low Temperature GEISSLER
23. Different Vacua Needed for Luminosity by Friction and by Dis-
charge ALVERGNIAT
24. Phenomena of Discharge around the Edges of an Insulating Sheet.
STEINMETZ
25. Highest Possible Vacuum Considered as a Non-conductor. ..MORGAN
26. Constant Potential at the Terminals of a Discharge Tube.
DE LA RUE and MULLER
260. Polarity of Discharge-tube Terminals in Secondary of Ruhmkorff
Coil. Mathematical Deductions , KLINGEN-BERG
27. Pressure in Discharge Tube Produced by a Spark.
KINNERSLEY, HARRIS, and RIESS
CHAPTER II.
28. Actions of Magnetism upon the Arc and Flame.
DAVY, BANCALARI, and QUET
29. Rotation of Luminous Discharge by a Magnet. Application in Ex-
plaining Aurora Borealis DE LA RIVE '
30. Action of Magnet on the Cathode Light. Relations Different ac-_
cording to the Position Relatively to the Magnetic Lines of
Force PLUCKER and HITTORF
31. Discharge Retarded Across, and Accelerated Along, the Lines of
Magnetic Force THOMSON, J. J.
32. Resistance of Luminosity of the Discharge Afforded by a Thin Dia-
phragm ' THOMSON, J. J.
33. Forcing Effect of the Striae at a Perforated Diaphragm SOLOMONS
CHAPTER III.
34. Electric Images RIESS
35. Electrographs on Photographic Plate by Discharge.
SANDFORD and McKAY
36. Positive and Negative Dust Pictures upon Lines Drawn by Elec-
trodes LlCHTENBERG
360. Photo-electric Dust Figures HAMMER
36^. Dust Portrait HAMMER
37. Electrical Images by Discharge Developed by Condensed Moisture.
KARSTEN
37. Magnetographs r v , . , McKAY
38. Bas-relief Facsimiles by Electric Discharge PILTCHIKOF
39. Distillation of Liquids by Discharge GERNEZ
40. Striae. Black Prints on Walls of Tube DE LA RUE and MULLER
viii CONTENTS.
CHAPTER IV.
41. Discharge Tube in Primary Current. Striae. Least E.M.F. Required.
GASSIOT
42. Current Interrupted Inside of Discharge Tube instead of Outside.
POGGENDORFF
43. Source of Striae at the Anode. Color Changed by Change of Cur-
rent .................................... DE LA RUE and M ULLER
44. Dark Bands by Small Discharges Disappear on Increase of Current,
and Appear Again by Further Increase ................ SOLOMONS
45. Motion of Striae. Method of Obtaining Motion when Desired and of
Stopping the Same ............................... SPOTTISWOODE
^ 46. Motion of Striae Checked at the Cathode. Tube, 50 ft. Long. The
Anode the Starting-point ......................... THOMSON, J. J.
47. Electrolysis in Discharge Tube ....................... THOMSON, J. J.
48. Heat Striae without Luminous Striae ......... DE LA RUE and MULLER
49. Sensitive State. Method of Obtaining. Telephone Used to Prove
Intermissions ....................... SPOTTISWOODE and MOULTEN
49. Cause of Sensitive State Detected by Telephone.
SPOTTISWOODE and MOULTEN
50. Sensitive State Illustrated by a Flexible Conductor within the Dis-
charge Tube ....................... REITLINGER and URBANITZKY
51. System of Operating Discharge Tubes. Excessively High Potential
and Enormous Frequency ................................ TESLA
52. Discharge-tube Phenomena by Self-induced Currents ........ MOORE
CHAPTER V.
53. Dark Space around the Cathode ................. . ......... CROOKES
54. Relation of Vacuum to Phosphorescence ................... CROOKES
55. Phosphorescence of Objects within Discharge Tube ........ CROOKES
56. Darkness and Luminosity in the Arms of a V Tube ........ CROOKES
Y 57. Cathode Rays Rectilinear within the Discharge Tube ....... CROOKES
58. Shadow Cast within the Discharge Tube ................... CROOKES
X 580. Mechanical Force of Cathode Rays. Wheel Caused to Rotate.
CROOKES
I 59. Action of Magnet upon Cathode Rays in Discharge Tube . .CROOKES
60. Mutual Repulsion of Cathode Rays in Discharge Tube ..... CROOKES
-^ 61. Heat of Phosphorescent Spot .............................. CROOKES
6ia. Theoretical Considerations of Thomson (Kelvin).
page 46. Velocity of Cathode Rays .................. THOMSON, J. J
page 47. Cathode Rays Charged with Negative Electricity. . .PERRIN
en's Photograph of Mt. Blanc Not Due to Cathode Rays.
62. Phosphorescence of Particular Chemicals by Cathode Rays.
GOLDSTEIN
63. Spectrum of /'^^/'-phosphorescence of Discharge Tube Compared
with that of Red-hot Metals ............................. . KIRN
63^. Chemical Action on Photographic Plate by Cathode Rays Inside of
Discharge Tube ....................................... DE METZ
63^. The Passage of Cathode Rays through Thin Metal Plates within
the Discharge Tube (no 64) ............................ HERTZ
,
6i^/
CONTENTS. IX
CHAPTER VI.
-f 65, top of page 53. Cathode Rays Outside of the Discharge Tube whose
Exit is an Aluminum Window. A Glow Outside of the Window.
LENARD
65, end of page 53. Properties of Cathode Rays in Open Air. ... ..LENARD
66. Phosphorescence by Cathode Rays Outside of the Discharge Tube.
LENARD
66<z. Transmission Tested by Phosphorescence.
67. The Aluminum Window a Diffuser of Cathode Rays. . .' LENARD
68. Transmission of External Cathode Rays through Aluminum and
Thinly Blown Glass LENARD
69. Propagation of External Cathode Rays. Turbidity of Air. ..LENARD
70. Photographic Action by External Cathode Rays and at Points beyond
the Glow. No Other Chemical Power Probable. Shadows of
Objects by Light and by External Cathode Rays Compared. No
Heat Produced by External Cathode Rays LENARD
</ 71. External Cathode Rays and the Electric Spark Distinguished.
Aluminum Window Not a Secondary Cathode LENARD
72. Cathode Rays Propagated, but Not Generated, in the Highest Pos-
sible Vacuum. Air Less Turbid when Rarefied LENARD
720:. Cathode Rays, while Traversing the Exhausted Observing Tube,
Deflected by a Magnet. No Turbidity in a Very High Vacuum.
LENARD
72^. An Observing Tube for Receiving the Rays and Adapted to be Ex-
hausted LENARD
73. Phenomena of Cathode Rays in an Observing Tube Containing Suc-
cessively Different Gases at Different Pressures. Phosphores-
cent Screen Employed for Making the Test LENARD
74. Cause of the Glow Outside of the Aluminum Window. Glow Not
Caused by External Cathode Rays. Sparks Drawn from the
Aluminum Window. Transmission of External Cathode Rays
Dependent Alone upon the Density of the Medium LENARD
v/ 75. External Cathode Rays of Different Kinds Variably DMused. Theo-
retical Observations LENARD
76. Law of Propagation of External Cathode Rays LENARD
77. Charged Bodies Discharged by External Cathode Rays. Discharge
at Greater Distances than Phosphorescence. Not Certain as to
the Discharge Being Directly Due to Intermediate Air.. .LENARD
78. Source, Propagation, and Direction of Cathode Rays General Con-
clusions '. . .DE KOWALSKIE
CHAPTER VII.
79 X-rays Uninfluenced by a Magnet. Source of X rays Determined by
Magnetic Transposition of Phosphorescent Spot ROENTGEN
80. Source of X-rays may be at Points within the Vacuum Space. Dif-
ferent Materials Radiate Different Quantities of X rays.
ROENTGEN
8r. Reflection of X rays ROENTGEN
82. Examples of Penetrating Power of X-rays ROENTGEN
83. Permeability of Solids to X-rays Increases Much More Rapidly than
the Thickness Decreases ROENTGEN
< CONTENTS.
\ 84. X-rays Characterized. Fluorescence and Chemical Action.
ROENTGEN
85. Non-refraction of X-rays Determined by Opaque and Other Prisms.
Refraction, if Any, Exceedingly Slight ROENTGEN
86. Velocity of X-rays Inferred to be the Same in All Bodr.ss. .ROENTGEN
87. Non-double Refraction Proved by Iceland Spar and Other Materials.
ROENTGEN and MAYER
88. Rectilinear Propagation of X-rays Indicated by Pin-hole Camera and
Sharpness of Sciagraphs ROENTGEN
89. Interference Uncertain Because X-rays Tested were Weak.
ROENTGEN
90. Electrified Bodies, whether Conductors or Insulators, or Positive or
Negative, Discharged by X-rays. Hydrogen, etc., as the Inter-
mediate Agency ROENTGEN
9Ort. Application of Principle of Discharge by X-rays ROENTGEN
90,4, b, c, d. Supplementary Experiments on Charge and Discharge by
X-rays. .MINCHIN, RIGHI, BENOIST, HERMUZESCU, and BORGMANN
91. Focus Tube ROENTGEN, SHALLENBERGER, et al.
girt. Tribute to the Tesla Apparatus ROENTGEN
92. X-rays and Longitudinal Vibrations ROENTGEN
93. Longitudinal Waves in Luminiferous Ether by Electrical Means
Early Predicted by , THOMSON (KELVIN)
94. Theory as to X-rays Being of a Different Order of Magnitude from
those so far Known SCHUSTER
95. Longitudinal Waves Exist in a Medium Containing Charged Ions.
Theoretical THOMSON, J. J.
96. Practical Application of X-rays Foreshadowed BOLTZM ANN
97. The Sciascope MAGIE, SALVIONI, et al.
CHAPTER VIII.
970. Electrified Bodies Discharged by Light of a Spark, and the Estab-
lishment of a Radical Discovery HERTZ
97/5. Above Results Confirmed and More Specific Tests.
WIEDEMANN and EBERT
98. Negatively Charged Bodies Discharged by Light. Discharge from
Earth's Surface Explained by Inference and Experiment.
ELSTER and GEITEL
99. Relation between Light and Electricity. Cathode of Discharge Tube
Acted upon by Polarized Light and Apparently Made a Conductor
Because of the Discharging Effect ELSTER and GEITEL
99,410992". Briefs Regarding Action between Electric Charge and
Light.
SCHUSTER, RIGHI, STOLSTOW, BRANLY, BORGMANN, MEBIUS, et al.
CHAPTER IX.
100. Stereoscopic Sciagraphs THOMSON, E.
101. Obtaining Manifold Sciagraphs Simultaneously upon Superposed
Photographic Films and through Opaque Materials, and thus
Indicating Relative Sensitiveness of Different Films to X-rays.
Intensifying Process Applicable in Sciagraphy. Thick Films
Appropriate THOMSON, E.
CONTENTS. XI
loirt. Sciagraph Produced through 150 Sheets of Photographic Paper.
LUMIERE.
102. Discharge Tube Adapted for Both Unidirectional and Alternating
Currents ........................... THOMSON, E. , and, SWINTON
103. X-rays. Opalescence and Diffusion.
THOMSON, E.. PUPIN, and LAFAY
IO3. Diffusion and Reflection in Relation to Polish ........ INBERT, et ah
104. Fluorometer. Fluorescing Power of Different Discharge Tube-s
Compared ......................................... THOMSON, E.
105. " Modified Sciascope for Locating the Source and Direction of
X-rays. Phosphorescence Not an Essential Accompaniment in
Production of X-rays .............................. THOMSON, E.
106. X-rays from Discharge Tube Excited by Wimshurst Machine. Full
Details Given of the Electrical Features.
RICE, PUPIN, and MORTON
107. Source of X-rays Determined by Projection through a Small Hole
upon Fluorescent Screen Adjustable to Different Positions.
RICE
io7<z. Use of Stops in Sciagraphy .................... LEEDS and STOKES
107^. X-rays from Two Phosphorescent Spots.
MACFARLANE, KLINK, WEBB, CLARK, JONES, and MORTON
108. Source of X-rays Determined by Shadows of Short Tubes ..... STINE
109. Instructions Concerning Electrical Apparatus for Generating X-rays.
STINE
no. Apparent Diffraction Really Due to Penumbral Shadows ..... STINE
iioa. Non-diffraction ........................................... PERRIN
in. Source of X-rays Tested by Interceptance of Assumed Rectilinear
Rays from the Cathode .................. SCRIBNER and M'BERTY
112. Source of X-rays on the Inner Surface of the Glass Tube Deter-
mined by Pin-hole Images ...... SCRIBNER and M'BERTY, PERRIN
II2. Anode Thought to be the Source. Cause of Error Suggested.
DE HEEN
113. Pin-hole Pictures by X-rays Compared with Pin-hole Images by
Light to Determine the Source. X-rays Most Powerful when the
Anode is the Part Struck by the Cathode Rays ........... LODGE
114. Valuable Points Concerning Electrical Apparatus Employed.
LODGE
115. X-rays Equally Strong during Fatigue of Glass by Phosphorescence.
LODGE
\ln6. Area Struck by Cathode Rays Only an Efficient Source when Posi-
tively Electrified ............ ROWLAND, CARMICHAEL, and BRIGGS
117. Transposition of Phosphorescent Spot and of Cathode Rays with-
out a Magnet .............. SALVIONI, ELSTER, GEITEL, and TESLA
II7. Molecular Sciagraphs in a Vacuum Tube. . ..HAMMER and FLEMING
CHAPTER X.
118. X-rays Begin before Strise End ........... EDISON and THOMSON, E..
119. Reason why Thin Walls are Better than Thick ............. EDISON
120. To Prevent Puncture of Discharge Tube by Spark .......... EDISON
121. Variation of Vacuum by Discharge and by Rest ........... EDISON.
Xll CONTENTS.
122. External Electrodes Cause Discharge through a Higher Vacuum
than Internal EDISON
123. Profuse Invisible Deposit from Aluminum Cathode.
EDISON and MILLER
f s *24. Possible Application of X-rays. Fluorescent Lamp.
EDISON and FERRANTI
1240. Greater (?) Emission of X-rays by Easily Phosphorescent Ma-
terials PlLTCHIKOF
125. Electrodes of Carborundum EDISON
126. Chemical Decomposition of the Glass of the Discharge Tube De-
tected by the Spectroscope EDISON
127. Sciagraphs. Duration of Exposure Dependent upon Distances.
EDISON
^28. Differences between X-rays and Light Illustrated by Different Pho-
tographic Plates. Times of Exposure.
EDISON, FROST, CHAPPUIS, IMBERT, BERTIN-SANS, and MESLIN
129. Size of Discharge Tube to Employ for Given Apparatus. . . .EDISON
130. Preventing Puncture at the Phosphorescent Spot EDISON
131. Instruction Regarding the Electrical Apparatus. . EDISON and PUPIN
132. Salts Fluorescent by X-rays. 1800 Chemicals Tested EDISON
133. X-rays Apparently Passed around a Corner. Theoretical Considera-
tion by Himself and Others.
EDISON, ELIHU THOMSON, ANTHONY, et al.
134. Permeability of Different Substances to X-rays. A List of a Variety
of Materials EDISON and TERRY
I34. Illustration of Penetrating Power of Light HODGES
135. Penetrating Power of X-rays Increased by Reduction of Tempera-
ture. Tube Immersed in Oil, and the Oil Vessel in Ice. X-rays
Transmitted through Steel \ in. Thick EDISON
136. X-rays Not Obtainable from Other Sources than Discharge Tube.
EDISON, ROWLAND, et al.
CHAPTER XL
137. Kind of Electrical Apparatus for Operating Discharge Tube for
Powerful X-rays TESLA and SHALLENBERGER
138. How to Maintain the Phosphorescent Spot Cool TESLA
139. Expulsion of Material Particles through the Walls of a Discharge
Tube . TESLA
I39. Giving to X-rays the Property of Being Deflected by a Magnet.
LAFAY and LODGE
139/5. Penetration of Molecules into the Glass of the Discharge Tube.
GOUY
140. Vacuum Tubes Surrounded by a Violet Halo... TESLA and HAMMER
141. Anaesthetic Properties of X-rays TESLA and EDISON
^142 and 142^. Sciagraphs of Hair, Fur, etc., by X-rays. Pulsation of
Heat detected TESLA, MORTON, and NORTON
143. Propagation of X-rays through Air to Distances of 60 ft TF.SLA
144. X-rays with Moderate Vacuum and High Potential TESLA
145. Detailed Construction and Use of Single Electrode Discharge Tubes
for Generating X-rays TESLA
CONTENTS. Xlll
146. Percentage of Reflection TESLA and ROOD
1460. Reflected and Transmitted Rays Compared. Practical Application
of Reflection in Sciagraphy. Analogy between Reflecting Power
of Metals and their Position in the Electro-positive Series.
TESLA
147. Discharge Tube Immersed in Oil. Rays Transmitted through Iron,
Copper, and Brass, i in. Thick TESLA
148. Bodies Not Made Conductors when Struck by X-rays TESLA
149. Non-conductors Made Conductors by a Current APPLEYARD
150. Electrical Resistance of Bodies Lowered by the Action of Electro-
magnetic Waves MINCHIN
CHAPTER XII.
151. Sciagraphic Plates Combined 'with Fluorescent Salts.
PUPIN, SWINTON, and HENRY.
152. Penetrating Power of X-rays Varies with the Vacuum.
THOMPSON, S. P.
153. Reduction of Contact Potential of Metals by X-rays MURRAY
'""154. Transparencies of Objects to X-rays Not Influenced by the Color.,
Detected by Simultaneous Photographic Impressions.
NODON, LUMIERE, BLEUNARU, and LABESSE
155. Chlorine, Iodine, Sulphur, and Phosphorus Combined with Organic
Materials Increase Opacity MESLANS, BLEUNARD, and LABESSE
^156. Application of X-rays to Distinguish Diamonds and Jet from Imita-
tions BUGUET, GASCARD, and THOMPSON, S. P.
157. Inactive Discharge Tubes Made Luminous by X-rays DUFOUR
158. Non-refraction in a Vacuum BEAULARD
^"159. Bas-relief Sciagraphs by X-rays CARPENTIER and MILLER
^^60. Transparency of Eye Determined by Sciagraph of Bullet Therein.
WUILLOMENET
161. Mineral Substances Detected in Vegetable and Animal Products.
RANWEZ
162. Hertz Waves and Roentgen Rays Not Identical ERRERA
163. Non-mechanical Action by X-rays Determined by the Radiometer.
GASSART
164. X-rays within Discharge Tube BATTELLI
""*> T6s. Combined Camera and Sciascope BL ( < YER
166. Non-polarization of X-rays THOMPSON, S. P., MACINTYRE
167. Diffuse Reflection. Dust Figures Indirectly by X-rays
THOMPSON, S. P.
168. Continuation of Experiments in 113 LODGE
169. Thermopile Inert to X-rays PORTER
170. Non-diffraction of X-rays MAGIE
171. Resistance of Selenium Reduced by X-rays GILTAY and HAGA
Total number of sections to this place, 199.
XIV CONTENTS.
CHAPTER XIII.
200. Needle Located by X-rays and then Removed HOGARTH
201. Needle Located at Scalpel by X-rays and then Removed. . . .SAVARY
202. Diagnosis with Fluorescent Screer. RENTON and SOMERVILLE
203. Bullet Located by Five Sciagraphs MILLER
204. Bones in Apposition Discovered by X-rays and afterward Remedied
by Operation. Other Cases MILLER
2040. Necrosis MILLER
205. Application of X-rays in Dentistry MORTON
206. Elements of the Thorax MORTON
207. A Colics' Fracture Detected by X-rays MORTON
208. Motions of Liver, Outlines of Spleen, and Tuberculosis Indicated.
MORTON and WILLIAMS
209. Osteomyelitis distinguished from Perriostitis.
LANNELONGUE, BARTHELEMY, and OUDIN.
210. Concluding Miscellaneous Experiments Relating to Similar Applica-
tions of X-rays.
ASHURST, PACKARD. MULLER, KEEN, and MORTON, T. G.
CHAPTER XIV.
Theoretical Considerations, Arguments, and Kindred Radiations.
ANTHONY
INTRODUCTION.
THE new form of energy, for which there are two names to wit,
the Roentgen ray and the X-ray is radiated from a highly exhausted
discharge tube, which may be energized by an induction coil or
other suitable electrical apparatus, such as a Holtz or a Wimshurst
electrical machine. 106. The principle underlying the construc-
tion of the usual induction (or Ruhmkorff) coil is disclosed in the
subject-matter of 1,2, and 3, and is represented in diagram in Figs,
i and 2 on page 17. It would be well for the amateur or general
scientific reader to study these sections carefully, for then he will
have all the knowledge that is necessary for understanding the ap-
paratus by which the discharge tube is energized. Of course, he
will not comprehend the various mechanical details, nor the many
electrical and mathematical relations existing in connection with an
induction coil, but he will gain sufficient knowledge to appreciate
what is intended when such a device is referred to here and there
throughout the book. Since the time of Faraday, Page, and Fizeau
induction coils of very large dimensions have been constructed, but
none of them probably ever exceeded that built by Spottisvvoode, dur-
ing or about 1875, which was so powerful as to produce between the
two electric terminals, in open air, a spark of 42 in. in the second-
ary current with only 30 small galvanic cells of the Grove tvpe in
the primary circuit. The cells are seldom used in this connection
at the present time, the same being replaced by the dynamo, and the
current being conveniently obtained from the regular incandescent-
lamp circuit which may be found in almost any city. Those, there-
fore, who intend to become better acquainted with the details of the
electrical apparatus should study in conjunction with this book
some elementary treatise relating particularly to dynamos and elec-
tric currents.
XVI IN TROD UCTION.
The essential element in connection with the generation of
X-rays is not the coil nor the dynamo, but the electric discharge,,
especially when occurring within a rarefied atmosphere, provided
within a glass bulb, called the discharge tube throughout the
book, but which has usually been called by different names, for ex-
ample, the receiver of an air pump, or a Geissler tube, when the air
is not very highly exhausted, or a Crookes tube (see picture at
123) when the vacuum is definitely much higher by way of contrast.
It has also been called a Hittorff tube, the Lenard tube, and by
several other names, according to its peculiar characteristics.
For those who are not acquainted with the nature of the electric
charge and discharge, nor with the peculiar and exceedingly in-
teresting phenomena which various investigators have discovered
from time to time, nor with the variety of effects according to the
nature and the pressure of the atmosphere within the glass bulb, it is
exceedingly difficult to understand with any degree of satisfaction
the properties, principles, laws, theories, and manner of application
of cathode and X rays. Consequently, the greater part of the book
treats of the electric charge and discharge in conjunction with cer-
tain kindred phenomena. Primarily, the meaning of the electric
discharge may be derived by referring to Fig. 2, page 17, where
there is shown an electric spark, indicated by radial lines between
the terminals of- a fine wire forming the long and fine coil or second-
ary circuit. Imagine that the wires are at great distances apart.
Let them be brought closer and closer together. By suit-
able tests it will be found, for example, that no current passes
through the wire, but when the points are brought sufficiently close
together a spark will occur between the two terminals. 2. Some-
times instead of what is understood as a spark, a brush or glow takes
place ( 10 and n), and in fact a numerous variety of effects occur,
a general name for all being conveniently termed an electric dis-
charge. Even if no sudden discharge takes place, yet, as when the
terminals are far apart, there may be a charge or a tendency, or, as
it is technically called, a difference of potential, between the two
electrodes, one of which is the cathode and the other the anode.
This is comparable to a weight upon one's hand, tending continually
to fall, and always exerting a pressure, and it will fall when the hand
FIG. i. HEAD.
FIG. 2. BROKEN ARM, OVERLAPPING.
(Due to defective setting.)
FIG. 4. KNEE, KNICKERBOCKER BUTTONS,
BULLET IN FEMUR.
FIG. 3. RIBS.
FROM SCIAGRAPHS BY PROF. DAYTON C. MILLER. 204.
XVI 1 1 IN TR OD UCTION.
is suddenly removed. This is in the nature more of an analogy than
of an exact correspondence. A discharge through open air, while
adapted to produce a great many curious as well as useful effects,
does not act as a generator of X-rays. 136, Another class of
phenomena is obtainable by exhausting the air to a certain extent
from a discharge tube, thereby obtaining what is usually called a
low vacuum. Such bulbs have been called Geissler tubes. Neither
can X-rays be generated therefrom to any practicable extent, but
only feebly if at all. 118. Hittorff, Varley ( 6i#), Crookes ( 53
to 61, inclusive), were the first to discover and study the different
phenomena that are obtained by diminishing the pressure within the
discharge tube to a decrement of several thousand millionths of an
atmosphere. This will explain why so many allusions have been
made to the Crookes tube, for when the electric discharge is caused
to take place in such a high vacuum X-rays are propagated in full
strength.
Upon the first announcement of the discovery, electricians, em-
inent and otherwise, were of one mind in assuming the possibility of
obtaining Roentgen rays from other sources than that of the highly
evacuated discharge tube. Instead of speculating and theorizing,
hosts of crucial tests were instituted, resulting negatively, and it is
now safe to conclude that the electric discharge is the only primary
:source, and it is reasonably safe to assert that the discharge must
take place within a highly evacuated enclosure.
The next stage of exhaustion, of no advantage to be considered,
is that at which no discharge takes place ( 25), and neither are any
Roentgen rays propagated therefrom.
CHAPTER I.
1. FARADAY'S EXPERIMENT, 1831. SECONDARY CURRENT BY
INDUCTION. Experimental Researches, Proc. Royal. So. 1841. In
brief, the experiment involved the elements illustrated in the
accompanying diagram, Fig. i, p. 17; a ring made of iron ;
upon the ring, two coils of copper wire, suitably insulated from
each other and from the iron ; a galvanometer included in cir-
cuit with one coil, and an electric battery of ten cells placed in
circuit with the other coil. He found that upon breaking or
completing connection with the battery, the needle was power-
fully deflected. Without entering into further detail, it is im-
portant, however, to notice that he did not perform any
experiments tending to establish the principle of increase of
E. M. F. by making the very slight change now known to be
necessary. 2.
2. PAGE'S EXPERIMENT, 1838. ELECTRIC SPARK BY INDUCED
CURRENT. Pynchon, p. 427. Dr. Page performed an experiment
in which the primary coil was but a few feet in length, while
the secondary coil was 320 ft. He included, in the primary cir-
cuit, only a few cells of battery. The manner in which he first
caused rapid interruptions of the circuit of the primary coil was
by the use of what may be called a coarse file, Fig. 2, p. 17.
He discovered that the E. M. F. during the rapid interruption
was so much increased over that of the small battery, that an
electric spark would pass between the secondary terminals with-
out first bringing them into contact with each other. 6. The
result of these experiments was not only the generation of a
current of high E. M. F. from a generator of low E. M. F., but
also a current of great quantity as .compared with currents ob-
tained from frictional and influence machines, whose complete
history is found in Mascart's work on Electricity.
3. FIZEAU'S EXPERIMENT. SPARK IN SECONDARY INCREASED
BY CONDENSER IN PRIMARY, 1853. Pynchon, p. 456. He connect-
ed the plates of a condenser respectively to the terminals of an
automatic circuit breaker in the primary circuit, and noticed
that the sparks between the two terminals of the interrupter
produced by the self-induced current were greatly diminished,,
while .thoset of : the sor|daTy coil were about double in length.
Since tha time it has been universally customary to equip induc-
tion coils with condensers in like manner.
4. VINCENTINI'S EXPERIMENT. CONDITION OF A GAS AROUNI>
A LIVE WIRE. Nuovo Cimento, Vol. XXXVI. , No. 3. Nature,
Lon., March 28, '95, p. 514. The Elect., Lon., Feb. 8, '95, p. 433.
G. Vincentini and M. Cinelli found that the molecules of a gas
at and near the surface of a platinum wire, rendered incandescent
by a current, are electrified, and that with hydrogen their poten-
tial is about .025 volt above the mean po-
tential of the wire. With air and carbonic
acid gas the increment is about i volt. The
apparatus, Fig. II., consists essentially of
means for passing a current along a platinum
LL iflr wire, a bulb for preventing draughts, and an
electrometer having a platinum disc electrode
that could be adjusted to different positions. It was noticeable
that the electrification did not reach a maximum instantaneously
upon closing the current through the wire, but the time was
less at points below the wire than above.
5. HENRY'S EXPERIMENT. MAGNETIZING RADIATIONS FROM AN
ELECTRIC SPARK. Proc. Inter. Elect. Cong., 1893, p. 119. Preece
alluded to Prof. Henry's original experiment illustrating the
action of an electric discharge 2 at a distance. He placed a
needle in the cellar. Disruptive discharges of a Leyden jar at
30 ft. distant, in an upper room, produced a magnetic effect
upon the needle.
6. FARADAY'S EXPERIMENT. ARC MAINTAINED BY CERTAIN
METALLIC ELECTRODES AT Low VOLTAGE. Experimental Re-
searches. Phil. Trans., Se. IX., Dec., 1894. 1074 to 1078.
The generator employed in this experiment consisted of a few
cells of a chemical battery, and he obtained, what he called, a
voltaic spark. He observed that when the two terminals touched
each other, a burning took place and an appearance as if the
spark were passing on making the contact, the terminals being
pointed and formed of metal. When mercury was the terminal,
the luminosity of the spark was much greater than with platinum
or gold, although the same quantity of current passed in both
cases. He attributed the difference to a greater amount of
combustion in the case of mercury, than in those of gold and
platinum. He obtained almost a continuous spark by bringing
down a pointed copper wire to the surface of mercury and with-
drawing it slightly. Wheatstone, in 1835, analysed the light of
sparks, and found them to be so characteristic that by means of
the prism and the spectra formed, the metal could be known.
7. WURTS'S EXPERIMENT. NON-ARCING METALS AT HIGH VOLT-
AGE. Trans. Amer. Inst. Elect. Eng. March 15, 1892. Ann. Chem.
Phar. Sup. VII, 354 and VIII, 133. Chem. News, VII, 70; X, 59,
and XXXII, 21, 129. Mendelejeff and Meyer discovered that
chemical elements occur in natural groups by a principle which
they termed the periodic law. One of these groups includes zinc,
cadmium, mercury and magnesium; and another group, anti-
mony, bismuth, phosphorus and arsenic. Alex. J. Wurts, of the
Westinghouse Electric Co. found that the metals of these groups
are non-arcing, by which he means that with an alternating cur-
rent dynamo of a thousand or more volts, and with the said
metals as electrodes in the air only just escaping each other, it
is impossible to maintain an arc as in the case of an ordinary arc
lamp having carbon electrodes or in a lightning arrester usually
having copper electrodes. He suggested and theorized that
certain chemical reactions served to explain the phenomena.
With low voltage as 500, the arc was maintained between all
metals. 6. A two pole lightning arrester is shown in Fig.
III. The arc formed, ceased instantly. One of the best metals
for practical use is an alloy of y? zinc and %
antimony, or any metal electroplated with a
non- arcing metal. Freedman observed a crit-
ical point with electrodes of brass. The cur-
rent was gradually reduced until the arc be-
XTTTTA came like the discharge of a Holtz machine
whose condensers have been disconnected. See Elect. Power,
N. Y., Feb. 1896, p. 119.
8. WHEATSTONE'S EXPERIMENT. DURATION OF SPARK. Phil.
Tran. 1834. The short duration of an electric spark produced
by a single disruptive discharge is easily made apparent by a
rapidly rotating disc, having radial sectional areas of different
colors. With reflected sunlight, the colors seem to blend into
one tint upon the principle of the persistence of vision; (See
vS wain's experiment. Trans. R. So. Edin. '49 and ,'6i.); but when
viewed by the flash of a spark, the colors are seen as distinctly
separated as if the disc were at rest. By calculation, based dir-
ectly upon a series of experiments, he found the duration of the
spark to be about .000042 sec. It was discovered also, by the
rotating mirror, that the apparently single spark was composed
of several following each other in quick succession, and he con-
cluded that the current during the discharge was intermittent.
He considered each of the divisons of the spark as an electric
discharge. Prof. Nichols, of Cornell University, and McKittrick
obtained curves indicating the variation of E. M F. during the
existence of a spark. Trans. Amer. Inst. Elect. Eng. May 20, '96.
Sa. Feddersen, who used a Leyden jar, modified the experi-
ment by having high resistances in the circuit through which
the charge was effected. The duration of the spark was found
to be increased. In one experiment, he employed a slender
column of water as the resistance, 9 mm. in length. The spark
endured .0014 second. With a tube of water 180 mm. the dur-
ation was .0183 second. He noticed also that the duration in-
creases directly with the striking distance and with the electrical
dimensions of the electrical generator. By varying the resist-
ance of the circuit, he found as it became less, the discharge was
intermittent, when further reduced, continuous, (difficult to ob-
tain) 1 1 and when very small, oscillatory i. e., alternately in
opposite directions.
9. FARADAY'S EXPERIMENT. BRUSH DISCHARGE SOUND. Phil.
Trans. Jan. 1837. Se. XII. The brush discharge was caused to
occur, in his experiments, generally from a small ball about .7
of an inch in diameter, at the end of a long brass rod, acting as
the anode. With smaller balls he noticed that the pitch of the
sound produced was so much higher as to produce a distinct
musical note, and he suggested that the note could be employed
as a means of counting the number of intermissions per second.
See Mayer's book on "Sound " 77, on measuring number of
vibrations in a musical note.
ga. Upon bringing the hand toward the brush the pitch in-
creased. 49. With still smaller balls and points, in which case
the brush could hardly be distinguishable, the sound was not
heard. He alluded to the rotating mirror of Wheatstone as be-
coming not only useful but necessary at this stage. He consid-
ered the brush as the form of discharge between the contact and
the air or else some other non or semi-conductor, but generally
between the conductor and the walls of the room or other ob-
jects which are nearest the electrodes, the air acting as the die
lectric. One experiment, he performed with hydrochloric acid
led him to believe that that particular gas permitted of a dark or
invisible discharge. Sometimes the air was electrically charged
4 to a less distance than the length of the brush or light.
10. BRUSH IN DIFFERENT GASES. STRIAE CATHODE BRUSHES.
In the air, at the ordinary pressure he found the color to be
" purple;" when rarefied still more purple, and then approach-
ing to rose; in oxygen, at the ordinary pressure, a dull white;
when rarefied, "purple;" and with nitrogen, the color was particu-
larly easily obtained at the anode, and when nitrogen was rare-
fied the effect was magnificent. The quantity of light was
greater than with any other gas that he tried. Hydrogen, as to its
effect, fell between nitrogen and oxygen. The color was green-
ish grey at the ordinary pressure and also at great rarity. The
striae were very fine in form and distinctness, pale in color and
velvety in appearance, but not as beautiful as those in hydrogen.
With coal gas, the brushes were not easily produced. They
were short and strong and generally green, and more like an
ordinary spark. The light was poor and rather grey. Also in
carbonic acid gas the brush was crudely formed at the ordinary
pressure as to the size, light and color. The tendency of the
discharge in this case was always towards the formation of the
spark as distinguished from the brush. When rarefied, the light
was weak, but the brush was better in form and greenish to
purple, varying with the pressure and other circumstances. As
to hydrochloric acid, it was difficult to obtain a brush at the
ordinary pressure. He tried all kinds of rods, balls and points,
and while carrying on all these experiments he kept two other
electrodes out in the air for comparison, and while he could not
obtain any satisfactory brush in the hydrochloric acid gas, there
were simultaneously beautiful brushes in the air. In the rare-
fied gas, he obtained striae of a blue color.
He compared the appearances also of the anode and cathode
brushes in different gases at different pressures. He noticed
that in air, the superiority of the anode brush was not very mark-
ed ( 41 at end.) In nitrogen, this superiority was greater yet. A
line of theory ran through Faraday's mind in connection with
all these experiments, whereby he held that there is "A direct
relation of the electric forces with the molecules of the matter
concerned in the action." 47. He made a practical applica-
tion of the principles in the explanation of lightning, because
nitrogen gas forms -f of the atmosphere, and as the discharge
takes place therein so easily.
u. GLOW BY DISCHARGE. GLOW CHANGED TO SPARK. Moxioii
OF AIR. CONTINUOUS DISCHARGE DURING GLOW. The glow w
most easily obtained in rarefied air. The electrodes were of
metal rods about .2 of an inch in diameter. He also obtained
a glow in the open air by means of one or both of the small
rods. He noticed some peculiarities of the glow. In the first
place, it occurred in all gases and slightly in oil of turpentine.
It was accompanied by a motion of the gas, either directly from
the light or towards it. He was unable to analyze the glow into
visible elementary intermittent discharges, nor could he obtain
FROM MAGNETOGRAPHS BY PROF. McKAY. p. 25.
T. Platinum wire.
2 Copper gauze.
3. Iron gauze.
10. Lead-foil.
11. Aluminum.
4. Tin-foil. 7. Silver coin.
5. Gold-foil. 8. Platinum -foil.
6. Brass protractor. 9. Brass.
12. Magnesium ribbon.
13. Copper objects.
FROM SCIAGRAPH OF VARIOUS OBJECTS, p. 130.
By Prof. Terry, U. S. Naval Academy.
any evidence of such an intermittent action, Sa. No sound
was produced even in open air. 9. He was able to change the
brush into a glow by aiding the formation of a current of air at
the extremity of the rod. He also changed the glow into a
brush by a current of air, or by influencing the inductive action
near the glow. The presentation of a sharp point assisted in
sustaining or sometimes even in producing the glow ; so also
did rarefaction of the air. The condensation of the air, or the
approach of a large surface tended to change the glow into a
brush, and sometimes into a spark. Greasing the end of the
wire caused the glow to change into a brush.
12. LULLIN'S EXPERIMENT. SPARK. PENETRATING POWER./
PASSAGE THROUGH SOLIDS. Encyclo. Brit. Article Electricity.
He placed a piece of cardboard between two electrodes and dis-
covered that a spark penetrated the material and left a hole
with burnt edges. When the electrodes were not exactly oppo-
site each other, the perforation occurred in the neighborhood of
the negative pole. Later experiments have shown that a glass
plate, 5 or 6 cm. in thickness, can be punctured by the spark of
a large induction coil. The plate should be large enough to
prevent the spark from going around the edges. The spark is
inclined, also, to spread over the surface of the glass instead of
piercing it, 24. Glass has been cracked by the spark in some
experiments.
13. FACE'S EXPERIMENT. SPARK. PENETRATING GLASS. HOLES
CLOSE TOGETHER. PRACTICAL APPLICATION. La Nature, 1879.
Nature, Dec. 26, 1879, p. 189. The length of the spark from the
secondary coil in air was 12 cm. One terminal of the secondary
passed through an ebonite plate (18 cm. x 12) and touched the
glass. Olive oil was spread around said terminal ( 1 1 at end),
and served to insulate the same. Oil dielectric in this connec-
tion originally employed at least prior to 1870. Remembered
by Prof. Anthony as far back as 1872, who often performed the
experiment according to instructions contained in a publication.
The other terminal of the secondary coil was brought against
the glass opposite the first terminal. The spark was then
passed and the glass perforated, 12. By pushing the glass
along to successive positions and passing the spark at each
movement, holes could be made very close together. In Nature,
of 1896, the author noticed that certain manufacturers were
introducing glass perforated with invisible holes to be used for
windows as a means of ventilation without strong draughts.
Perhaps the fine holes were made by means of the electric
.spark.
8
14. KNOCHENHAURER'S EXPERIMENTS. CONDUCTING POWER or
GAS. SPARK. PENETRATING POWER. RELATION OF E. M. F. TO
PRESSURE OF GAS. 1834. Pogg. Ann., Vol. LVIL. and Gordon,
Vol. II. Boltzmann's experiment (Pogg. Ann., CLV., '75), and
calculation indicated that a gas at ordinary pressure and tem-
perature must have a specific resistance at least io 26 times that
of copper. Pogg. Ann., CLV., '75. Sir William Thomson (Kelvin)
confirmed this limit for steam, and Maxwell the same for mer-
cury and sodium vapor, steam and air. From Maxwells MSS.
Herwig was not sure but that the Bunsen burner flame and
mercury vapor conducted. He allowed for the conductivity of
the walls of the glass container. Braun treated of the conduc-
tivity of flames. Pogg. Ann., '75.
140. Varley found that 323 Daniel cells only just initiated a
current through a hydrogen Geissler tube, and only 308 cells
continued the current after once started. Knochenhaurer found
that Harris' (Phil. Trans., 1834) law did not hold exactly true-,
and that the ratio between the E. M. F. and the air pressure be-
comes greater and greater as the pressure becomes less and less.
Harris thought the ratio was constant. The limits of his pres-
sures were from 3 to 27.04 inches of mercury. Stated in other
words, his results were the same as those of Harris and Masson
(Ann. de Chimie, XXX., 3rd Se.), except that a small constant
quantity should be added. 16.
15. GORDON'S EXPERIMENT. DUST PARTICLES HASTEN DIS-
CHARGE. Gordon, Vol. II. Other experimenters had investi-
gated the phenomena of the electric spark with different densi-
ties of the dielectric by a spark produced by a frictional or an in-
fluence machine, or, in a few cases, by powerful batteries without
coils, while Gordon claims to be the first to carry out these experi-
ments with an induction coil. He observed that when the dis-
charging limit was nearly reached, small circumstances, such as
a grain of dust or a rusting of the terminal by a former discharge,
would cause the discharge to take place at a lower E. M. F., which
should be allowed for.
1 6. KELVIN'S EXPERIMENT. Proc. R. So., 1860. Enclyco. Brit.,
Art. Elect. He used as the terminals, two plates. One of them
was perfectly plane, while the other had a curvature of a very
long radius. The object of this arrangement was to obtain a
definite length of spark for each discharge. The plates were
gradually moved away until the spark would no longer pass,
and the reading of the distance was noted. The law which he
found cannot well be expressed in the form of a rule or prin-
ciple, because it is of a rather intricate nature, but a discovery
1 9
resulted, namely in the case where the distance was greater, the
dielectric strength was smaller for respective distances of .00254
and .535 cm. Many theoretical considerations in reference to
this matter have been presented, notably that of Maxwell in his
treatise on Electricity and Magnetism, Vol. I.
17. CAILLETET'S EXPERIMENT. SPARK. PENETRATING POWER.
HIGH PRESSURES. INCREASED DIELECTRIC STRENGTH. Mascart,
Vol. I. He experimented with dry gas up as high as pressures
of 700 Ibs. per sq. inch. He found that the dielectric strength
continues to increase with increase of pressure. He used about
15 volts in the primary and a powerful induction coil. The die-
lectric strength was so great that at the maximum pressure
named above, the spark would not pass between the electrodes
when only .05 mm. apart. 25 and n, near end.
18. FARADAY'S EXPERIMENT. DISCHARGES IN DIFFERENT CHEM-
ICAL GASES VARIABLY RESISTED. Exper. Res. Phil. Trans. , Se.
XII., Jan. '36. Faraday passed on from the consideration of
tne effect of pressure, temperature, etc., and wondered whether
there would be any difference in the law according to what gas
was used. He arranged apparatus so that he could know, with
air as a standard, whether another gas had a greater or less di-
electric power. (Cavendish before him had noticed a difference.)
He tabulated the results. They exhibited the following facts,
namely that gas, when employed as dielectrics, depend for their
power upon their chemical nature. 10. Hydrochloric acid gas
was found to have three times the dielectric strength of hydro-
gen, and more than twice that of oxygen, nitrogen or air; there-
fore the law did not follow that of specific gravities nor atomic
weights. See also De la Rue, Proc. Royal So., XXVI., p. 227.
19. THOMSON'S EXPERIMENTS. GAS AS A CONDUCTOR. VISIBLE
INDICATION BY DISCHARGE. Nature, Lon., Aug. 23, '94, p. 409 ;
Jan. 31, '95, p. 332, and other references cited below, Lee. Royal
Inst. Proc. Brit. Asso., Aug. 16, '94. In making comparisons,
things of like nature should be considered. Take, for example,
gas at .01 m. The number of molecules in such a rarefied at-
mosphere is comparatively small, while in an electrolyte there
are molecules sufficient in number to produce 15,000 Ibs. of
pressure, if imagined in the gaseous state within the same space.
By an experiment and rough calculation, Prof. J. J. Thomson,
F.R.S., calculated that the conductivity of a gas estimated per
molecule is about 10 million times that of an electrolyte, for ex-
ample, sulphuric acid. 14. This is greater than the molecular
conductivity of the best conducting metals. The experiment
which is illustrated in Fig. IV. was a second experiment which
IO
did not serve as a basis for calculation, but exhibited very
strikingly to the eye that gases having different pressures have
different conductivities. For this ap-
paratus he had two concentric bulbs, as
indicated, one being contained within
the other. The inner one had air rarefied
to the luminous point. The outer one
had a vacuum as high as it was practical
to make it, and contained in a projection
a drop of mercury, which, when heated,
would gradually increase the pressure.
Two Leyden jars were employed, and
their outer coatings were connected to
the coil which is seen surrounding the outer bulb, and the inner
coatings were connected to the coils of a Wimshurst machine.
The operation was as follows : When the mercury was cold,
that is, with a high vacuum in the outer compartment, a bright
discharge passed through the inner bulb, while the outer bulb
was dark. When the mercury was heated, the outer bulb was
bright, and the inner one was almost dark. By well known
principles of conductors and non-conductors, the operation was
explained by Prof. Thomson, who assumed that the gas in the
outer bulb is a conductor ; then, at each spark will the alternat-
ing current in the coil induce currents of an opposite direction
in the gas, which will become luminous, as occurred when the
mercury was heated. The currents circulating in the gas act
as a shield to the induction of the currents in the inner bulb.
However, with the vacuum exceedingly high in the outer bulb,
the air therein being a non-conductor comparatively, or for the
given E. M. F., does not prevent the discharge through the inner
bulb, which becomes, therefore, luminous. He next compared
the dielectric power of a gas, a liquid and a solid. He found
that the E. M. F. had to be raised, in order to produce the dis-
charge, higher in the liquid than in the gas, and higher in the
solid than in the fluid. 12.
20. BOLTZMAN, GlBSON, BARCLAY, HoPKINSON AND GLADSTONE'S
EXPERIMENTS. SQUARE ROOT OF THE DIELECTRIC CAPACITY
EQUAL TO THE REFRACTIVE INDEX. Phil. Trans., 1871, p. 573.
Maxwell, Vol. II., 788. Maxwell has argued elaborately upon
results of some of the above experimenters upon the theory
that the luminiferous ether is the medium for transmission of
electricity, light and magnetism ; therefore he predicted that
the relation stated in the title above should exist. He acknowl-
edged that the relation is sufficiently near a constant to show
II
in connection with other results, especially those obtained, that
his theory is probably correct.
21. PLUCKER'S EXPERIMENT. HERMETICALLY SEALED VACUUM
TUBE. Encycl. Brit. vol. 8, p. 64. Pogg. Ann. 1858, and vol.
CXXXVI, 1869. He engaged Geissler (according to Hittorf) to
make a glass tube in which the platinum wire electrodes were
sealed in the glass by fusion, as in the modern incandescent lamp.
After the air was exhausted by a mechanical air pump through
a capillary tube, the same was sealed with the flame of a spirit
lamp. He thus established means whereby a practically per-
manent vacuum could be maintained within a glass bulb. Plat-
inum expands by heat at about the same rate as glass: hence
there is no tendency to crack and admit air.
22. GEISSLER'S EXPERIMENT. LUMINOSITY OF VACUUM TUBES
BY FRICTION. INCREASED BY LOW TEMPERATURE. Science Record,
1873. By rubbing the vacuum tubes with an insulator cat skin,
silk, etc. he observed that light was generated and that its color
depended upon the particular gas forming the residual atmos-
phere. At a low temperature, the colors were more luminous.
1 35. The best form of tube consisted of a spiral tube contained
within another tube. A modified construction involved the
introduction of mercury. By exhausting the air, snd shaking the
tube, the friction or motion of the mercury against the glass pro-
duced luminous effects according to the gas. Only chemically
pure mercury would cause the light, which endured for an in-
stant after the rubbing ceased. 63.
23. ALVERGNIAT'S EXPERIMENT. LUMINOSITY OF VACUUM
TUBES BY FRICTION AND DISCHARGES. DIFFERENT VACUA RE-
QUIRED. Set. Rec., 1873, p. in. Comptes Rendus, 1873. To obtain
luminosity by charging the tubes with the coil, it was necessary
to increase the degree of the vacuum but when this was done
the rubbing of the tube would not cause light. The tube em-
ployed was 45 cm. in length, and contained a small quantity of
silicic bromide. The atmospheric pressure within the tube for
obtaining the glimmer by friction was 15 mm.
24. STEINMETZ'S EXPERIMENT. LUMINOUS EFFECTS BY ALTER-
NATING CURRENT AND SOLID DIELECTRICS. Trans. Amer. Inst.
Elec. ng., Feb. 21/93. In carrying on experiments in the
accurate measurement of dielectric strength, he noticed that
upon placing mica between the electrodes, as is hereinafter
set forth, a spark did not at first form, but that which he called
a corona. He attributed the appearances to a condenser phe-
nomenon, or at least he suggested this as an explanation. 3.
As soon as the corona reached the edge of the plate, the
12
disruptive discharge took place, by means of the sparks passing
over the edge of the dielectric. 38. He employed an alter-
nating current dynamo of about 50 volts and i h. p., frequency
of 150 complete periods per second. The E. M. F. of the alter-
nator was varied, by changing the exciting current, up to 90
volts. Step- up transformers were employed. With a difference
of potential in the secondary of 830 volts, and a thickness of mica
of 1.8 mm. and when the experiment was performed in a dark
room a faint bluish glow appeared between the mica and the
electrodes; At 970 volts the glow was brighter, while at 1560
volts the luminosity was visible in broad day -light, and kept on
increasing with the increase of E. M. F. He modified the experi-
ment by using mica of a thickness of 2.3 mem. The difference
of potential was 4. 5 kilo-volts. In addition to the bluish glow,
violet streams or creepers broke out and increased in number
and length as the E. M. F. became greater, forming a kind of
aurora around the electrodes and on both sides of the mica sheet.
A loud hissing noise occured. 9. As soon as the corona
reached the edges of the mica, the disruptive discharge occurred
in the form of intensely white sparks and it was noticeable that
the length of these sparks was 10 fold greater than could be
obtained in the air at 1 7 kilo-volts. These sparks were so hot
as to oxidize the mica, as apparent from the white marks re-
maining. The electrodes also became very hot, and the mica
was contorted and finally broke down.
25. MORGAN'S EXPERIMENT. No DISCHARGE IN HIGH VACUA,
Wiedemann, vol. 2. Phil. Trans., 1875, vol. 75. He was led to be-
lieve by an experiment, that when the vacuum is sufficiently
perfect, no electromotive force could drive the spark from one
terminal to the other, however close together they may be. 18.
Details of Morgan's Experiments were as follows, given roughly
in his own words:-A mercurical gauge about fifteen inches long,
carefully and accurately boiled till every particle of air was ex-
pelled from the inside, was coated with tin-foil five inches down
from its sealed end, and being inverted into mercury through a
perforation in the brass cap which covered the mouth of the
cistern, the whole was cemented together and the air was ex-
hausted from the inside of the cistern, through a valve in the
brass cap, which, producing a perfect vacuum in the gauge, form-
ed an instrument peculiarly well adapted for experiments of
this kind. Things being thus adjusted (a small wire having
been previously fixed on the inside of the cistern, to form a com-
munication between the brass cap and the mercury, into which
the gauge was inverted), the coated end was applied to the con-
13
ductor of an electrical machine, and notwithstanding every ef-
fort, neither the smallest ray of light nor the slightest charge
could ever be procured in this exhausted gauge.
26. DE LA RUE AND MULLER'S EXPERIMENT. CONSTANT
POTENTIAL AT THE TERMINALS OF A DISCHARGE TUBE. Phil.
Trans., part i, vol. 169, p. 55 and 155. The apparatus consisted
of an exhausted bulb, a chloride battery of 2400 cells and a large
resistance adapted to be varied between very wide limits. The
result was a constant potential at the electrodes of the bulb,
during all the variations of the resistance. They concluded,
therefore, that the discharge in highly rarefied gases is disrup-
tive, the same as in air at ordinary pressure.
z6a. KLINGENBERG'S CALCULATIONS. DIRECTION OF DISCHARGE
TUBE CURRENT IN SECONDARY OF RUHMKORFF COIL. Translated
from the German, by Ludwig Gutmann. Extract of paper read by G.
Klingenberg before the Electro-technischer Verein. It would natur-
ally be inferred that an induction coil, the primary current of
which is intermitted, and of one direction, would produce an
alternating current in the secondary coil. The fact of the matter
is, however, that a good induction coil will produce the sparking
only in but one direction. 41. The reason is the following: If the
coil had no self-induction nor capacity, then the current impulses
would be represented by a rectangle a, Fig. i. On closing, the
current would suddenly reach its maximum, which is deter-
mined by the terminal pressure and circuit resistance, and this
current strength would be maintained as long as the circuit re-
mained closed. On the opening of the circuit, the current would
decrease just as suddenly ; if not, the arc on opening of the cir-
cuit would oppose such sudden fall, therefore the corner will be
slightly rounded at a, Fig. 2. The influence of self-induction,
which we find in any coil, is the force that will tend to oppose
any change in the current strength. Therefore, the self-induc-
tion will be the cause of a retardation of the minimum current.
On the other hand, it increases the size of the spark on opening.
Next a condenser is enclosed in the main circuit, so that the
spool is closed through it at the moment the current is inter-
cepted. If we assume, for simplicity sake, that the magnetiza-
tion of the iron is proportional to the current strength, then the
primary current curve represents at the same time, the curve of
14
the rate of change of line of force in the magnetic field. The
secondary E. M. F. is determined by e. = n -ULt /; the rise then
dt
will have a smaller E. M. F. than at the fall, like Fig. 3, except that
the curve representing the fall should be shown as more nearly
perpendicular to the abscissa.
27. KlNNERSLEY, HARRIS AND RlESS'S EXPERIMENTS. SPARK.
PRESSURE PRODUCED BY. Ganot, 790, et al. Encyclo. Brit. Art.
Elect. These experimenters passed a spark through air contained
over mercury, so that if the pressure of the air were increased,
the mercury would move along through a capillary tube, having
a scale so that the amount could be represented to the eye, as in
the cut. (Fig. V.) The experiments proved that when a spark
passes through the air, the pressure is
increased, and it was concluded in view
of several experiments, that the spark
being the source of an intense, but small
amount of heat, expanded the air, there-
by causing the pressure in a secondary
manner, through the agency of heat. A
V spark as short as 2 mm. will produce a
considerable pressure of the mercury. Riess performed an ex-
periment also in causing the spark to pass through cardboard,
and also through mica located within the air chamber. 12.
Other things being equal, the increase of temperature was less
by using the solid material like mica or cards, than without
This illustrated that a part of the energy of the spark was con-
verted into heat and a part into mechanical force, and explained
why sound, 24, is produced by a spark and by lightning.
CHAPTER II.
28. DAVY, BANCALARI AND QUET'S EXPERIMENTS. ELECTRIC
ARC, MAGNETISM AND FLAME. SOUND PRO-
DUCED. PRACTICAL APPLICATION OF ELEC-
TRIC ARC. Phil. Mag, 1801. When the
electric arc, for example between two car-
bon electrodes, occurs, in a powerful mag-
netic field, it is violently drawn to one side
as first shown by Sir. Humphry Davy, as
if the wind were blowing it and sometimes
it is broken into two parts. Fig. VI. Again
a loud noise is produced. 9. Without the
magnet, the appearance is as at the left.
With the energized magnet, the arc and light, as a whole, are
as shown at the right.
29. DE LA RIVE'S EXPERIMENT. ROTATION OF LUMINOUS EF-
FECT BY MAGNET. APPLICATION TO EXPLAIN AURORA BOREALIS.
Phil Trans., vol. 137, 1847. Pynchon, p. 471. Ganot, Sect. 958.
An oval discharge tube was employed, having a highly exhaust-
ed atmosphere (for those days) of spirits of turpentine. A cylin-
drically shaped pole of a magnet extended into the bulb half
way, Fig. 4, p. 17. The inner end of the magnetic pole formed
one electrode of the tube, and the other electrode was a ring
within the vacuum at the foot of the magnetic pole. A fountain
of light extended from one end of the magnet pole to the other,
and remained stationary, while the magnet was not energized;
but the light was condensed into an arc and travelled around the
magnet pole when a current was passed through the coils of the
magnet. For similar action of magnet on a flexible and mov-
able wire carrying a current, see experiments of Spottiswoode
and Stokes, Proc. R. So.^ 1875. The aurora borealis rotates
around the pole of the earth, and therefore, De La Rive thought
that the phenomenon in his laboratory and in nature were but
one and the same thing and different only in degree. He also
extinguished an arc in open air by means of a powerful magnet.
15
i6
30. PLUCKER AND HITTORF'S EXPERIMENTS. ACTION OF MAG-
NET ON CATHODE COLUMN OF LIGHT. Pogg. Ann., 1858 and 1869.
Plucker found that the magnet acts on the cathode light in a
rarefied atmosphere in a different manner from that on the
anode light. In the former the light follows the magnetic
curves and strike the side of the bulb, according
to position of the poles, see Fig. VII. " Where
the discharge is perpendicular to the line of the
poles, it is separated into two distinct parts,
which can be referred to the different action ex-
erted by the electro-magnet on the two extra
currents produced in the discharge." Ganot. 925.
31. THOMSON'S EXPERIMENT. A DISCHARGE RETARDED ACROSS
AND ACCELERATED ALONG THE LINES OF MAGNETIC FORCE.
Nature, Lon., Jan. 31, 1895, p. 333. Lect. Royal Inst. Prof. J. J.
Thomson, F. R. S., performed an experiment which illustrates
that the electrical discharge is retarded in flowing across the
lines of magnetic force and accelerated in flowing with or paral-
lel to such lines. As illustrated in Fig. 20, p. 17, he employed a
large electro-magnet adapted to be cut in and out of circuit. He
had two air chambers, one a bulb, indicated by a circle, and the
other a tube bent into a rectangle, indicated by the dotted square.
Between these, was an adjustable coil having its terminals con-
nected to the outside coatings of Ley den jars. When the dis-
charge took place between the poles of the magnet, that is, in
the direction of the lines of force, the discharge was helped along
by the magnetic field, but when it took place across the bulb,
that is, across the lines of force, the discharge was retarded.
" The coil can be adjusted so that when the magnet is 'off ' the
discharge passes through the bulb, but not round the square
tube; when, however, the magnet is 'on,' the discharge passes
in the square tube but not in the bulb."
32. THOMSON'S EXPERIMENT. RESISTANCE OFFERED TO STRIAE
BY A THIN DIAPHRAGM. Lect. Royal Inst. Nature, Lon. Jan. 31,
'95, p. 333. It has often been remarked that lightning always
takes the easiest path. The same has been noticed with refer-
ences to the artificial electric spark. Prof. J. J. Thomson, F.R.S.
performed an experiment, which not only confirms this principle
but does so in an emphatic manner, and proves it true in refer-
ence to the electric discharge in rarefied gases. He arranged
a very thin platinum diaphragm so as to divide a Geissler tube
into two compartments, Fig. 19, p. 17. He then formed a pass-
age way around the diaphragm, which could be opened and
closed by mercury, by respectively lowering and raising the
3 {^ -fc
x /7777777T7 /
SOME EXPERIMENTS PRIOR TO LENARD'S.
i8
lower vessel of mercury along the barometer tube. When the
passage way is opened around the diaphragm, the luminosity
extends through the passage way in preference to going through
the diaphragm. When the passage way is closed by mercury,
the discharge goes through the thin metal plate. The same was
found to occur when the platinum leaf was replaced by a mica
scale.
33. SIR DAVID SOLOMON'S EXPERIMENT IN 1894. Proc. Royal
So., June 21, '94. Nature, Lon. Sept. 13, '94, p. 490. With a
tube having a perforated diaphragm, he noticed a " forcing effect *'
at and near the hole. The striae had the appearance of being
pushed through from the longer part of the tube the diaphragm
not being in the centre. There was no passage way around the
diaphragm only through the small puncture. 19.
CHAPTER III.
34. RIESS'S EXPERIMENT. ELECTRIC IMAGES. Jttess's Reibungs.
vol. 2, 739. He laid a coin upon a plate of glass and charged
the same electrically about one-half of an hour or more. Upon
removing the coin and sprinkling the plate with dust, an en-
graving of the coin was visible upon the glass. 13. A suitable
dust is licopodium powder.
35. SANFORD AND MCKAY'S EXPERIMENT. ELECTROGRAPHS.
ORIGINAL CONTRIBUTION BY PROF. McKAY OF PACKER INST.,
Brooklyn, May, '96. The picture of the coins in Fig. IX, was
produced by the apparatus shown in Fig. VIII, /, ^, tinfoil,/,
photographic plate with coins on sensitive side, all wrapped in
black paper. Fig. VIII represents the general arrangement for
taking electrographs. This particular one was made by remov-
ing the upper tinfoil and touching each coin successively with
wire from one of the poles, while the other wire was connected
with tinfoil on the opposite side. The condenser thus formed
is charged and discharged many times by a Holtz machine or
induction coil. This is not a new discovery, it was first discrib-
ed by Prof. Sanford, I think, of Leland Stanford University, two
or three years ago. Other claimants of earlier date probably
exist.
36. LICHTENBERG'S EXPERIMENT. DUST FIGURES. PICTURES
DRAWN WITH ANODE AND CATHODE. Go 'ttingen, 177 '8-79. MOTUM
FLUIDI ELECTRICITI. He drew two independent superposed pic-
tures upon a flat surface of an insulating material, for example,
rosin. One picture was drawn with one terminal of a charged
Leyden jar. Another picture was drawn with the other ter-
minal of a charged Leyden jar. He sprinkled upon the surface
over the two pictures, a dust made of a mixture of red lead and
sulphur powder. The former became attracted to the picture
drawn with the cathode, and the latter to that made with the
anode, so that the two figures were clearly visible. Before sprink-
ling the powders upon the surface it is necessary to stir them
together whereby they become oppositely electrified.
19
ARRANGEMENTS FOR TAKING ELECTROGRAPHS. 35, p. 19.
FROM ELECTROGRAPHS OF COINS. 35, p, 19.
Taken by Prof. McKay.
21
The sulphur arranges itself in tufts with diverging branches
and the red lead in small circular patches. The particular
materials, namely, the sulphur and
red lead were first used by Villarsy.
In case only one powder is employed,
for example, licopodium, it adheres
to both the positively and negatively
electrified portion of the insulating
plate, but in larger quantities upon
the latter portions. Fig. X, shows
rosin disc covered with licopodium
powder after touching the disc with
the knob of a Leyden jar.
360. HAMMER'S PHOTO-ELECTRIC DUST FIGURES. From per-
sonal interview. According 1 to experiments of Elster and Geitel,
hereinafter noted, 98, Hammer's dust figures shown in the
accompanying half-tone cut may possibly be accounted for on
the principle of the discharge of negatively electrified bodies by
light. Mr. William J. Hammer, Mem. Amer. Inst. Elect. Eng., has
a historical collection of incandescent lamps (Elect. Eng.> N. Y.,
April 29, '96, p. 446.) which were arranged on shelves in a glass
case standing obliquely in the sunlight about an hour a day After
the lapse of many months, the very fine dust within the case
lodged upon the inner surface of the glass in such a manner as
to produce oval dust figures corresponding somewhat to the
shapes of the lamps and some of them, appear after reproduction
by the half- tone process in the accompanying cut. When the
figures are inspected closely and the circumstances are known,
no one can doubt that the sun and lamps acted as agents in their
formation. As to the correct explanation, the matter has not been
sufficiently discussed by scientists (presented here for the first
time) to enable the author to render the opinions of others,
but it is of interest in connection with Roentgen rays and the
discharge of electrified bodies by light. As a matter of course,
the surfaces of the lamps would reflect thelight in such a way
as to make bright spots (movable, however, with the sun) upon
the glass of the containing case, and if the latter were in any
sense charged by negative atmospheric electricity, this light
would cause a variable amount of dust to be attracted accord-
ing to the intensity of the rays striking the glass. These remarks
are in the nature merely of a suggestion of a hypothesis. The
heavy curved, black line in the cut is a part of the frame of
the glass case. The incandescent lamps do not show, simply
because the case was empty when the photograph was taken.
FIG. i. HAMMER'S DUST-FIGURE ON GLASS. 36a, p. 21.
FIG. 2. HAMMER'S HISTORICAL COLLECTION OF INCANDESCENT LAMPS,
CONTAINED IN CASE HAVING THE DUST-FIGURES. 36a, p. 21.
2 3
That the figures were not due to chemical action was shown
by rubbing off some of the dust with the fingers. Finger marks
were pictured on the figures. Off hand, Mr. Hammer and Prof.
Anthony intimate air convection by differentiation of tempera-
ture, as a possible cause.
36^. Independently of the above peculiar phenomenon, Mr.
Hammer recently had on exhibition at the Electrical Exposition
of the National Electric Light Association in New York, 1896,
a portrait formed of fine dust upon a pane of glass. The circum-
stances were as follows, as remembered by the author. Mr.
Hammer happened to be in some place where an artisan was
removing a photograph from an old frame. The glass which
protected the protrait exhibited a f ac-simile in dust on the inner
surface. The glass had not been in contact with the photograph,
because of a thick passe-partous surrounding the picture.
Neither was the glass an old negative photographic plate.
Further test and inspection tended to prove that the dust picture
was executed by some action of the heat or light of the sun.
Prof. Benjamin F. Thomas, of the University of the State of
Ohio, in an interview, scarcely thought that the result was due
to convection, because the dust print was so sharply defined.
The principle of the discharge of bodies by light may be applic-
able perhaps, but further experiment would be necessary as a
more secure foundation. It is common to find the print of a
picture in a book upon the opposite page, being due merely to
the pressure of the inked surface, as in the art of printing. This
explanation cannot be applied to the dust portrait, because there
was no contact between the photograph and the glass.
37. KARSTEN'S EXPERIMENT. ELECTRICAL IMAGES DEVELOPED
BY CONDENSED MOISTURE. Riess's Reibungselect., vol. II., 739.
He arranged the following articles in the following order :
First, a metal plate suitably insulated ; secondly, a piece of a
glass plate on top of the metal plate, and, thirdly, a coin or small
metal object on top of the glass. Sparks were then allowed to
pass for several minutes from a Holtz or similar machine to the
coin. The image of the latter appeared by removing the glass
plate and breathing upon it. The bas-relief of the image on the
coin also was visible in all its details, appearing as in Sanford's
Electrograph, 35. Theoretical considerations led others to
believe that the figures of Riess and Karsten are due to a differ-
ent cause from that involved in the figures of Lichtenberg, for
the former are thought to be due to a molecular action of a
permanent nature upon an insulating material. A slight change
in the color often occurs, thereby outlining the object.
DUST-PORTRAIT ON GLASS, 36b, p. 23, DISCOVERED BY WILLIAM J. HAMMER,
Lighter portions, dust ; darker portions, due to less or no dust. Finger-marks across
the shoulder and at right. Exposure 8 years. Portiait as sharp and clear as a daguerreo-
type. During exposure in frame, distance of glass from photograph, 1/16 inch. Above half
tone was made from a photograph of the dust-portrait only after several unsuccessful
attempts by different photographers. The original dust-rortrait is scarcely visible. Let every
one examine closely glass plates when taken from old frames.
25
370. MCKAY'S EXPERIMENT. MAGNETOGRAPHS. FROM PER-
SONAL NOTES BY REQUEST. April, 1896. Although this ex-
periment does not belong to that class connected with discharge
tubes, yet the phenomenon has a theoretical interest in connec-
tion with X rays. He obtained a photograph of different ob-
jects in the dark by means of radiations from the poles of an
electro-magnet after two hours' exposure, but it need not have
been so long, as he obtained clear images in five minutes in one
experiment with frequent variations of current by means of a
rheostat, and by approach and recession of the armature. The
elements involved in the experiment were arranged in the fol-
lowing order : First, a large inverted magnet for supporting 100
Ibs., the poles hanging downward. Next in order was a wooden
board pressing flatwise against the ends of the . poles of the
magnet. Next, the objects and the sensitive plates backed
thereby and all enclosed in a completely opaque wrapping ex-
tending over the sides, face, back, etc., of these two elements.
Next in order was an armature about as heavy as the magnet
would support. The cut herein represents the photograph that
was produced of the different objects named. By reading Prof.
McKay's very detailed description in the Scientific American,
April 1 8, 1896, p. 249, the reader may feel certain that the pho-
tograph was not due to light for he tried the experiments in
different ways and with various precautions. In a course of ex-
periments carried on by student Austin, about Feb. 15, '96, in
the Dartmouth laboratory, a sciagraph of what appeared to be
the lines of force was obtained by means of X rays, but upon
repeating the experiment the result was negative. See Elect.
Engineer, Mar. IT, '96, p. 257. Article by E. B. Frost.
38. PILTCHIKOFF'S EXPERIMENT. LIQUID BAS-RELIEF FAC-
SIMILES BY ELECTRIC DISCHARGE. Pro. Acad. Sci., Paris, March,
'94. The Electr., Lon., April 13, '94, p. 656. These shadow
pictures were obtainable either with the
anode or cathode, the particular machine
employed being a large Voss. To either pole
was electrically connected a pointed wire
which was held just above the surface of
castor oil, in a copper pan. A remarkable
effect was obtained of the shadow of a piece
of mica, Fig. XI, of whatever shape, located
between the point and the surface. 24.
Let it be observed that this shadow was not
one in the sense of light and darkness but it consisted of a
plateau within a depression, the former being of tihe same
26
shape as though it were a shadow of the mica triangle. To
illustrate the experiment better, let the mica be supposed to be
removed, then will there be a depression formed in the oil upon
bringing the metallic point near to the surface. Now insert the
insulating sheet between the point and the surface, then will
there be an elevation within the depression of the same shape
that the shadow would be.
39. GERNEZ'S EXPERIMENT. DISTILLATION OF LIQUIDS BY DIS-
CHARGE. Phys. So., Paris, 1879. Nature, Nov. 20, 1879, p. 72. In
order that the apparatus with which he experimented may be
understood, imagine a tube standing vertically in another tube.
The two concentric tubes communicate with each other at the
top only. The Holtz machine is the generator. The liquids in the
two tubes at the beginning stand at the same level. Sparks are
passed through the adjacent air, which is in contact with both
liquids. The liquid at the cathode rises and at the anode falls.
38. Such was the experiment performed by Gernez. He was
inclined to conclude that the effect was due to "An electrical
transport of liquids along the moistened surfaces of the tubes."
When the liquid was alcohol, it actually went over as by distilla-
tion, three times as fast as water. A soluble salt in water in-
creased the rate of distillation; and so also did the addition of a
small quantity of sulphuric acid or ammonia. No distillation
of bisulphide of carbon, tetra chloride of carbon, nor turpentine
occured. Query: Can alcohol be concentrated or practically
distilled upon this principle ?
40. DE LA RUE AND MULLER'S EXPERIMENT. STRIAE. BLACK
PRINTS ON WALLS OF TUBE. Phil. Trans., 59, '78. Particles of
the metal of the electrodes were deposited upon the inside of the
glass forming permanent black striae qr bands 44, at points
corresponding to the spaces between the luminous striae. 6,
near the end.
CHAPTER IV.
41. GASSIOT'S EXPERIMENT. STRIAE. TUBE IN PRIMARY CUR-
RENT. CURRENT VIBRATORY. Phil. Trans., '59, p. 137. Bakerian
Lectures. Phil. Trans., '58, p. i. Proc. R. So., x., pp. 36, 393,
404 ; xii., p. 329 ; xxiii., p. 356. The form of tube in which to
obtain luminous striae to the best advantage was that of a dumb-
bell with the electrodes located respectively in the balls after-
wards confirmed by Sir David Solomons, Bart. Proc. Royal So.,
June 21, '94. Nature, Lon., Sept. 13, '94, p. 490. He obtained
in the vacuum luminosity with 500 Daniell's cells, which he
found to be the least E. M. F. that could be employed. He
omitted, and apparently overlooked, the introduction of an au-
tomatic interrupter in the circuit and the use of a very low
E. M. F. 52. In conjunction with Spottiswoode, 1,080 cells of
chloride of silver (about 2,000 volts) were employed, first with-
out, and then with condensers. One of the condensers consisted
of the usual tinfoil type, and the other of a self-induction kind,
namely of about 1,000 feet of wire. The results were striae
with the condensers, and no striae without the condensers. 8a.
The results suggested to them that there was some relation in
principle between the striae and vibration of the current. They
therefore built an ingenious apparatus to test whether this was
true, or not, and they found such was the case by the following
related means. If a current passing directly from the primary
battery through the condenser and the discharge tube is undu-
latory or intermittent in any sense, then it would be able to in-
duce a current in the secondary of the induction coil. 8 at
centre. They found that there was a current thus induced, and
they detected it by means of a small discharge tube which be-
came luminous. Fig. 3 p. 17. This was an independent tube
near the top of the figure, having nothing to do with the one
containing straie, which were produced by the primary current
and shown at the right. Dr. Oliver Lodge, F.R.S., in treating
of the cathode and X rays in The Elect., Lon., Jan. 31,
'9 6 > P- 43 8 > stated the following with reference to Gassiot's ex-
27
28
periments: " In the days of Gassiot and other early workers
( 43) on the discharge in rarefied air, it was the stream from
the anode that chiefly excited attention. It is this which devel-
oped the well-known gorgeous effects which used to be shown
at nearly every scientific conversazione."
42. POGGENDORFF'S EXPERIMENT. EFFECTS QF INTERRUPTING
A CURRENT WITHIN DISCHARGE TUBE. Phil. Mag., 4th Se.,
vol. x., 1855, p. 203-207. Imagine an electric bell vibrator and
magnet within the glass receiver upon an air-pump. Upon
connecting the magnet and vibrator in series with a small elec-
tric battery, it is evident that in the open air, as usual in electric
bells, there will be a minute violet spark at the terminals of the
circuit breaker. 6. Now, let the air be exhausted as far as.
possible by means of a mechanical pump as constructed in 1855.
Poggendorff performed such an experiment, and he noticed that
in the poor vacuum the ordinary violet spark became yellow,
while blue light like a small enveloping tube surrounded the
hammer of the vibrator and wire leading to the opposite con-
tact and a little projection extending away from the hammer.
His experiment was unique, because showing for the first time
that a current from a battery, if interrupted in the vacuum, will
not only produce the usual minute spark, but that a blue tube
of light will be produced around the conductors within the va-
cuum.
43. DE LA RUE AND MULLER'S EXPERIMENT. SOURCE OF THE.
STRIAE AT THE ANODE. NUMBER OF STRAIE VARIED BY CHANGE
OF CURRENT. Phil. Trans., 1878. By an arrangement of means
for causing different pressures, they made a discovery, namely,
that as far as the eye is concerned the striae begin to have their
existence at the anode. 46. Imagine the internal gas pres-
sure to become less and less. First, a violet luminosity occurs
around the anode as in 42. As the pressure becomes less and
less, luminous striae move toward the cathode accompanied by
more and more striae, which increase either to form a column
reaching a certain distance or else extending through the whole
distance between the electrodes. 46. They observed that
when the E. M. F. was constant and the current changed, the
variation in the appearance of the striae was very regular. 41.
With some tubes the number of striae increased with the in-
crease of current, while with a decrease of current the number
of striae became less and less. Sa. With some tubes the num-
ber of striae increased while the current decreased. 8a. With
the use of a condenser, then as the E. M. F. decreased together
with a diminution of current, the number of striae varied. The
29
striae nearest the anode vanished first, as they diminished in
number with the fall of the E. M. F. The striae on the other
hand originated at the anode, when the oharge of the condenser
was gradually increased from a minimum, and then the striae
continued to increase from the anode as the source. As to the
color of the striae, the same was changed by an alteration of
the current.
44. SOLOMONS' EXPERIMENT. DARK BANDS BY SMALL DIS-
CHARGES. Nature, Lon., Sept. 13, '94. Proc. R. So., June 21,
'94. Solomons found that in a very dark room, striae (alternate
light and darkness) appeared with very minute discharges, and as
the current was increased, they vanished, appearing again when
the discharge was strong. He could not obtain them until the
luminous column Extended to the glass forming the large glass
tube. 40.
45. SPOTTISWOODE'S EXPERIMENT. GOVERNING THE MOTION OF
STRIAE. EFFECT UPON MOTION BY DIAMETER OF DISCHARGE
TUBE. MOTION STOPPED BY MAGNET. Proc. R. So., vol. 33, p.
455. Spottiswoode found that he could obtain motion when he
desired. He introduced some constant resistances and also a
rheostat of fine adjustment. The least change of resistance
caused some effect upon the striae. The general principle that
he established was that letting it be assumed that the striae are
stationary then; "An increase of resistance produces a forward
flow, and a decrease of the resistance a backward flow," differ-
ences of as little as i ohm in the primary current caused the
effect. Sometimes the velocity of the flow is fast and sometimes
slow, being so rapid in certain instances that the unaided eye
cannot distinguish them, but they are known to exist by the
use of the revolving mirror. 46. With tubes of small diameter,
compared with their length, he noticed the fact that the striae
in one portion of the tube moved faster than those in another
portion. 46. Sometimes one group moved while the other one
was stationary. Sometimes they moved in opposite directions.
This last named phenomenon occured also in very wide tubes.
The points at which the charge took place he called nodes. He
discovered external means for stopping this action. He did it
by means of a magnet located opposite one end of the tube. 31.
When the magnet was energized, all motion ceased. 31.
46. THOMSON'S EXPERIMENT. VELOCITY OF STRIAE CHECKED
AT THE CATHODE. Nature, Lon. Jan. 31, '96, p. 330. A tube
50 ft. long was exhausted, &a, as to striking distance. In this
particular experiment, he caused a single interruption in the
primary of the induction coil, and observed the motion of the
FROM SCIAGRAPH OF FOOT DEFORMED BY POINTED SHOES. 204.
By Prof. Miller.
V-4.
FROM HAMMER'S MOLECULAR SCIAGRAPH. nya, p. 114.
striae from the anode to the cathode by means of a rotating
mirror. 43. The luminosity began at the anode and travelled
toward the negative with a high velocity, but upon its arrival at
the negative pole its velocity was checked. He said that the
striae did not disappear at the cathode like a rabbit would in
entering a hole, but they lingered around the electrode for some
time. As a consequence of this delay, he found as expected, an
accumulation of positive electricity, 4, in the neighborhood of
the cathode. It is a general principle, therefore, that when a
discharge passes between a gas and metal, there is an accumula-
tion, illustrating that the discharge experiences a difficulty or
resistance. 32 and 33. The experimenter, Prof. J. J. Thomson,
acknowledged that Profs. Liveing and Davy had noticed similar
effects.
47. THOMSON'S EXPERIMENT. DISRUPTIVE DISCHARGE AND
ELECTROLYSIS. Nature, Lon. Jan. 31, '95. Lect. S. Inst. The
Electr., Lon. vol. 31, p. 291, 316, and vol. 35, p. 578. Trans. R.
So., '95. The discharge of electricity through conducting liquids
is, with scarcely an exception, (example, mercury) accompanied
by a chemical action. Faraday and Davy both performed early
experiments in this direction. Prof. J. J. Thomson has set
forth some instructive facts and which act as evidence that there
is a close relation between the disruptive discharge and chemical
action between the dielectric and electrodes. 6 and 7. He
made this experiment in connection with his investigations
relating to the difficulty the positive electricity experiences in
passing from a gas to the negative electrode. 46. He carried
this experiment further, by testing gases of different chemical
natures. The apparatus he employed consisted first of an alter-
nating current generator, a high tension converter, a bulb for
containing first one gas and then another, whose metal electrodes
were connected with the secondary of the transformer, and an
electrometer connected to a third electrode which could be
moved about within the bulb. The operation was as follows:
when the bulb contained oxygen which is an electro negative
gas, the third movable electrode received a positive charge in
whatever part of the bulb it was moved to, but with hydrogen
instead of oxygen at atmospheric pressure, the third electrode
received a positive charge far away from the arc between the
other electrodes, but very near the arc it received a negative
charge. He then rarefied the atmosphere of hydrogen and he
noticed that the space where the third electrode became negative,
contracted, and at about J of an atmosphere became practically
nothing, so that the said third electrode connected to the electro-
32
meter became slightly positive at all points within the hydrogen.
4. The next step consisted in using a bulb, having oxydized
copper electrodes and a hydrogen atmosphere at the pressure
where there was only positive electricity, that is about ^ of an
atmosphere. This remarkable phenomenon occurred; there was
no positive electricity, but only negative. When the copper
oxide was reduced, the positive electricity only, existed in all
parts of the bulb. In brief, bright copper electrodes left a posi-
tive charge in the gas, while oxydized electrodes left a negatve
charge. He argued upon the results of this experiment to
account for the delay in the passage of the electricity from the
gas to the metal, 46. In later experiments, he used the spectro-
scope to detect decomposition. 6, at end.
48. DE LA RUE AND MULLER'S EXPERIMENT. HEAT STRIAE.
Phil. Trans., vol. 159, 1878 They arranged for the best condi-
tions> that is, when a small number of striae occurred in con-
junction with a wide, dark interval. 44. They found that the
heat was greatest at the position of maximum luminosity, but
they also found that heat was generated at the dark spaces. A
novel feature was the discovery of the development of heat in
the middle of the tube even when there was no luminosity, 90,
near end, so that they thought it probable there may be what
might be termed heat striae, independently of luminous striae.
49. SPOTTISWOODE AND MOULTON'S EXPERIMENT. SENSITIVE
STATE. AIR-GAP IN CIRCUIT FORMS BEST METHOD OF OBTAIN-
ING. BRANCH CURRENT TO EARTH VERIFIED BY A TELEPHONE.
SENSITIVE STATE BY A SINGLE QUICK DISCHARGE. Phil. Trans.,
1879, p. 165, and April 8, 1880. By sensitive state of luminous
effects in a Geissler tube is meant the susceptibility of the light
,( 28) to an outside conductor connected to earth. Fig. 5, p. 17,
When one's hand is brought near a Geissler tube the change
near the hand sometimes occurs and sometimes it does not. 8.
In the first place, the effect is more easily noticeable if the vac-
uum tube is comparatively wide or thick in diameter. With the
electric egg, for example, the luminous effect, instead of extend-
ing more or less across the space between the electrodes, reaches
from one of the poles to a conductor on the outside of the egg,
provided said conductor has an earth connection or large capa-
city. Some of the light continues to exist nevertheless between
the two poles. The general principle is that the division exists
because of the redistribution or branching of the disruptive dis-
charge. It was not known why the luminosity should be affected
by such an outside conductor sometimes, and remain the same at
other times but the above named experimenters discovered causes
33
-which could be depended upon to produce the sensitive state.
The apparatus will be described. They had the usual Geissler
tube with the platinum wire electrodes, and a Holtz machine as
the generator. They were led to believe that intermissions of
the current had a great deal to do with the production of the
-sensitive state, and accordingly they arranged for an air-gap in
-circuit with the machine and with the vacuum tube. 51.
They not only observed that such a gap caused the sensitive
state, but that an increase in the length of the gap made the lu-
minous column more sensitive. They increased the gap .so
much that the ramifications of the light could be seen. If an
induction coil is employed as the secondary generator, a con-
denser should be coupled up in connection with it. The two in
combination thereby produce the sensitive state, but upon cut-
ting out the coil and charging the tubes from the condenser the
sensitiveness can not be detected. Instead of the permanent
air-gap, may be employed a rapid circuit interrupter, coupled up
between a Holtz machine and a vacuum tube. The manner of
coupling up is to place the interrupter in a shunt to the vacuum
tube. Difficulty had been found in early experiments to obtain
the sensitive state with those vacua which give striae. With a
rapid circuit interrupter and an induction coil, the breaks oc-
curring 240 per second, the luminous column was not only
broken up into striae, but were acted upon by the approach of
an outside conductor connected to earth. The sensitive state is
noL always made apparent by the appearance of attraction of
the luminous light to the outside conductor. Sometimes the
light seems to be repelled. These two phenomena may be
caused in the same tube. This feature of the sensitive state
constitutes the beginning of radiations of energy through the
walls of a vacuum bulb, like X rays. Some action or other in
these cases takes place through the glass They tried an ex-
periment in which one of the electrodes of the vacuum tube was
entirely on the outside. The electrical discharge was found to
be sensitive, for the discharge was changed in its appearances by
the presence of an outside conductor connected to earth. An-
other cause of the sensitive state was observed, namely, the
brevity of the charge. This may be illustrated with a Ley den
jar, which is known to give an almost practically instantaneous
discharge. A single discharge from such a jar produced a flash
of light which was in the sensitive state. The nomenclature by
which the experimenters denned the cause of the phenomena is
made up of the words : Re-distribution of electricity, and a re-
lief of the external strain.
34
No re- distribution took place unless the outside conduc-
tor was connected to earth or to a conductor of large capacity,,
nor would an outside conductor, which was already charged,
serve to exhibit the sensitive state. The re- distribution effect
was proved by means of a telephone connected in circuit be-
tween the outside conductor and the earth Fig. 5, p. 1 7. When the
state was sensitive, that is, during the use of the air-gap, the
telephone produced a sound in unison with the intermissions,
occurring at the air-gap. 9 and 90.
50. REITLINGER AND URBANITZKY'S EXPERIMENT. SENSITIVE
STATE ILLUSTRATED BY A FLEXIBLE CONDUCTOR WITHIN THE.
DISCHARGE TUBE. Proc. Vienna Acad., 1879. Nature, Nov. 20,
1879. The discharge tube was 20 ctm. long. It had the usual
platinum electrodes, and it stood upright. From the upper
electrode, was suspended a strip of tinfoil in the middle of the
tube, which was connected to a pump so that the density of the
gas could be varied. At atmospheric pressure, the secondary
current of a Ruhmkorff coil connected to the electrodes caused
the strip to be attracted to the glass tube. The attraction was
less and less as the process of exhaustion was carried on, and
when a pressure indicated by 7 mm. was reached, the strip was.
neither attracted nor repelled, but hung downward the same as
without any electricity whatever, but it was attracted by a neigh-
boring shell-lac rod which had been rubbed with cloth, and it
was repelled by a glass rod which had been rubbed with amala-
gam, it being assumed that the strip was connected to the anode.
36. The opposite action took place when it was connected to
the cathode. As the exhaustion continued and became greater
and greater, these actions died away also up to a rarefaction of
about 4 mm. Independently of the degree of rarefaction, the
flexible strip of tinfoil was always deflected by an outside con-
ductor connected to earth. 49.
51. TESLA'S EXPERIMENT. INCANDESCENT ELECTRODE BY HIGH
POTENTIAL AND ENORMOUS FREQUENCY. SYSTEM REFERRED TO
BY ROENTGEN FOR GENERATING POWERFUL X RAYS. U. S. Let-
ters Pat., No. 454,622, June 23, '91. Martin s Researches of Tesla\
Trans. Amer. Inst. Elec. Engineers, May 20, '91 ; Elec. Review,
N. Y., June 24, '93, p. 226 ; Lect. Franklin Inst., Feb. 24, '93, and
Nat. Elec. Light Asso., Mar. i, '93 ; also Lect. in Europe. Later
he again experimented in this direction, see Elec. Review, N. Y.,
May 20, '96, p. 263. By the U. S. Patent Office he was granted,
among other claims, the following : *' The improvement in the
art of electric lighting herein described, which consists in gen-
erating and producing for the operation of lighting devices,.
35
currents of enormous frequency and excessively high potential,
substantially as herein described." A simple combination of
circuits together with great skill in the construction of appar-
atus involving high powers of insulation, resulted in the produc-
tion, within a vacuum, of an electrode radiating intensely white
light. The circuit may be easily traced in the diagram Fig. 17
p. 17. Briefly described, there may be noticed an alternating
current generator of comparatively low E. M. F. The current
from this generates a secondary current by means of an induc-
tion coil. This secondary current generates a tertiary current
by a second induction coil. An air-gap for automatic and inter-
mittent disruptive discharges, 49 near end, is in the circuit of
the secondary coil of the first named induction coil, which is
directly charged by the alternating current generator. The gap
may be noticed between the two balls. In shunt to the air-gap
is a condenser (see Fizeau, chapter I.) represented by several
parallel lines. The lamp consists merely of an evacuated bulb
having an electrode of carbon or other refractory material,
which is connected to one pole of the last secondary coil while
the other pole may be outside, and may consist, for example,
of the walls of a room, which in such a case should be of some
electric conducting material. The higher the vacuum the more
intense the light; he found no limit to this rule. Fig. \6a p. 17
illustrates his ideal method of lighting a room. He found that
with two plates at a distance apart as indicated and connected
to the poles of the coil, and with electrodeless vacuum bulbs,
the latter became bright in space no mechanical or electrical
connection other than air and the assumed ether.
52. MOORE'S EXPERIMENT. LUMINOSITY IN DISCHARGE TUBE
BY SELF-INDUCED CURRENTS. Trans. Amer. Inst. Elect. Eng., Sept.
20, '93 and April 22, '96. Several U. S. Letters Patent. Invented
1892. During or about 1831, Prof. Henry discovered that when
the circuit of a primary battery was interrupted, a self-induced
current, which he called an extra current, was produced. When
the circuit was closed, there was also a self-induced current, but
very much feebler than that obtained on interruption. The
self-induced current occurred only at or about the instant of
interruption or completion. He found also that the self -induced
current produced by interruption was enormously increased in
E. M. F. if the circuit included a helix of very long and fine wire.
It was further increased by the presence of an iron core. With
one or two cells, the spark upon interruption was scarcely visi-
ble, but with a fine wire 30 or 40 feet long, an appreciable
spark was obtained during interruption. With but a compara-
36
lively few cells, and with a magnet for example like a telegraph
relay, the E. M. F. arose to several thousand volts at the instant of
interruption. D. McFarland Moore introduced into such a circuit
a Geissler tube and provided a rapid automatic interrupter. Page,
Ruhmkorff and others had, at an early date, noticed the desira-
bility, in operating Geissler tabes by secondary currents, to
obtain quick interruption in the primary circuit in order to pro-
duce the best effects in the Geissler tube. Moore caused the
interruptions to take place in a vacuum, so high that a disrupt-
ive electrical discharge could not pass. The break was therefore,
absolutely instantaneous and complete. By this system, illus-
trated in diagram in Fig. 18, p. 17, he obtained all the luminous
effects, actions by magnets, the sensitive state, striae and all the
other phenomena heretofore noticed in Geissler tubes and some
of those obtained by Tesla with his apparatus as just described.
In greater detail, it will be noticed that he had a dynamo of rather
low E. M. F., generally 100 volts, and a high vacuum containing a
circuit interrupter operated automatically by a magnet outside
like a vibrator in an electric bell. The magnet served also as
the self inductive device. The magnet and interrupter were in
series with each other, therefore, while the Geissler tube was in
series with the magnet, and the electrodes extended either
inside of the Geissler tube or remained on the outside. He per-
formed numerous experiments on similar lines and developed
the system on a large scale, whereby rooms (e. g. the hall of the
Amer. So. Mech. Eng,, N. Y.) have been illuminated as if by other
artificial illuminants, by employing long and numerous vacuum
tubes. Among several discoveries was that of the production
of a bright pencil of light along the axis of a long open helix,
which formed one of the internal electrodes. The Patent Office
made strenuous efforts to determine the degree of novelty,
assuming that some one else must have conceived the idea of
employing a self-induced current to operate Geissler tubes ; but
nothing nearer than Poggendorff's experiment 42 could be
found, and therefore the following claim (in patent 548576, Oct.
22, '95,) was granted among a hundred or so relating to develop-
ments and details and particularly covering the vacuum inter-
rupter. " The method of producing luminous effects, consisting
in converting a current of low potential into one of high poten-
tial, by rapidly and repeatedly interrupting the low potential
current in its passage through a self -inductive resistance, and
passing the former current through a Geissler tube, thereby
producing light within the tube."
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CHAPTER V.
53. CROOKES' EXPERIMENT. DARK SPACE AROUND THE CATH-
ODE. Lect. Brit. Asso. y She/., Eng., Aug. 22, '79. According to
Lenard (The Electr., Lond., Mar. 23, '94) Hittorf discovered the
cathode rays, and Varley, 6ia, and Crookes studied them.
The pressure of the residual gas was i M. of an atmosphere.
Prof. Crookes, F.R.S., maintained the evacuated space in com-
munication with the air pump and with an absorbent material.
Before his time most experimenters worked with a vacuum not
much less than 30,000 M. The first experiment is illustrated in
diagram, at Fig. 6 p. 17, but the vacuum was not the highest in
this type. The tube was cylindrical and was provided with
electrodes at the ends. Another electrode was located at the
centre and was made the cathode, while the two terminal elec-
trodes were made the same pole ; namely, the anode. Upon
connecting the tube in circuit with the secondary of a large in-
duction coil, the luminosity did not extend either continuously
or in striae throughout the length of the tube. Former investi-
gators had likewise noticed the dark space. The space and glass
on each side of the central cathode were dark. The dark space
extended for about one inch on each side of the negative pole.
It is not intended here, any more than in former cases, to present
theories in explanation further than to briefly allude to any con-
clusion at which the experimenter himself arrived. Crookes'
explanation of the phenomena has not been universally accepted,
nor has it been proved otherwise. The knowledge of the ex-
istence of rays, now known as Roentgen rays, will assist in for-
mulating theories upon the Crookes' phenomena and may either
confirm some of his views or overthrow them. Crookes con-
sidered that the residual atmosphere was in such a state as to
be as different in its properties from gas, as gas is from liquid
and liquid from solid, and therefore he named the attenuated
atmosphere radiant matter, or fourth state of matter. He con-
cluded that the remaining particles of the gas forming the
radiant matter moved in straight lines over a great distance as
39
-compared with that moved through by molecules at the ordinary
pressure. He called this distance the " mean free path.". If
his theory is correct, this dark space is due to the fact that the
molecules in motion at and near the cathode do not bombard
-each other and therefore do not produce the effect of light.
When the motion is arrested by particles of gas themselves,
within the bulb, then is light generated. The force propelling
the particles from the positive pole was supposed to be less. In
order to let the experiments speak for themselves, as much as
possible, without being too much influenced by the opinion of
the experimenter ; the theory is only briefly alluded to as above,
and will not be further applied in the presentation of his other
experiments. In view of the radical discoveries of Lenard and
Roentgen, after the installation of the Crookes phenomena, it
has been the policy of the author to present all the experiments
as facts for evidence in behalf of the general theories, which
may be hereafter formulated independently of old theories.
Therefore, the reader should bear in mind the teachings of the
various experiments with the view of arriving at general prin-
ciples and hypotheses.
. 54. RELATION OF VACUUM TO PHOSPHORESCENCE. He started
with such a high vacuum that he could not obtain any electrical
discharge. 25. There was, therefore, no phosphorescence in
the glass tube, whatever. The caustic potash, which had been
employed to absorb the last trace of moisture and carbonic acid
gas, was slightly heated, and very gradually. Then it was no-
ticed that a current began to pass and that the glass became
green, and apparently on the inner surface. As the heat con-
tinued, the green passed gradually away and was replaced by
striae, which first appeared to extend across the whole diameter
of the glass tube ( 40) which was a long cylindrical tube, and
then became concentrated toward the axial line of the tube.
Finally, the light consisted of a pencil of purple. 10. When
the source of heat was removed so that the moisture and car-
bonic acid gas could be absorbed again by the potash, the striae
appeared, and then the other effects just named, only in the re-
versed order, until the tube acted like an infinite resistance.
Phosphorescence is the correct word, because the light existed
for a few seconds after cutting off the current.
55. PHOSPHORESCENCE OF OBJECTS WITHIN THE VACUUM
TUBE. The construction in. Fig. 7, p. 17, shows how a diamond
was caused to phosphoresce within a Crookes' tube, being sup-
ported in a convenient manner in the centre of one of the tubes,
while electrodes were located near, the ends and were formed of
40
disks facing the diamond. Upon connecting the disks to the
respective poles of the secondary conductor, and by performing
the experiment in a rather dark room, the diamond became
brilliantly phosphorescent, radiating light in all directions. He
experimented with many substances in this way, but found that
the diamond was the best almost equal to one candle power.
In order to exhibit the phosphorescence of glass in a striking
manner, he charged three small tubes simultaneously. One
was mads of uranium glass which radiated a green light. An-
other was an English glass which appeared blue, and the re-
maining one was German glass which phosphoresced a bright
green. Notice difference with respect to light which does not
perceptibly cause phosphorescence of glass. The uranium glass
was the most luminous. Luminous paint, as prepared by
Becquerel, and later by Balmain, which has the property of
storing up light and afterwards radiating it in a dark room for
several hours, became more phosphorescent in the Crookes tube
than when subject to day-light. Phosphorescence of the min-
eral phenakite, the chemical name of which is glucinic alumin-
ate, was blue, the emerald, crimson, and spodumene, which is a
double silicate, were yellow. The ruby phosphoresced red,
whatever its tint by day-light. In one tube he had rubies of all
the usual tints by day-light, but they were all of one shade of
red by the action of the disruptive discharge in the tube.
56. DARKNESS AND LUMINOSITY IN ARMS OF V TUBE. See Fig.
8, p. 17. It will be noticed that in Fig. 6, p. 17, the tube was
straight. Crookes desired to see what effect would take place
in a bent tube. He therefore employed a V shaped tube, having
electrodes in the ends one in each arm. Upon causing the
electrical discharge to take place through the tube, one arm was
luminous and the other was dark. Whatever the E. M. F. was,
the appearances remained the same. No luminosity would bend
from one arm of the V shaped tube to the other. The cathode
arm was always luminous and the anode dark. With a less de-
gree of vacuum, both arms were luminous, according to early
experimenters who thus brilliantly lighted tubes of the most
fantastic shapes.
57. CATHODE RAYS RECTILINEAR. RADIATE NORMALLY FROM
THE SURFACE OF THE CATHODE. In his lecture he had, side by
side, two bulbs, one, in which the vacuum was of such a degree,
that a blue stream of light existed between the negative pole
and positive pole, 54, at centre. It is evident that the vacuum
in this bulb was not very high. Fig. 9, p. 17, shows a stream
extending from the negative to the positive pole, Fig. 10, p. 17,
is the same kind of a tube only the vacuum is about i to 2 M.
In other words, the vacuum in the latter was just so high that a
discharge took place, and instead of the luminous effect being
like that with a low vacuum, there was a patch of green light
directly opposite the concave negative pole. The radiations from
this pole were rectilinear, crossing each other at a focus within
the bulb and producing upon the glass a phosphorescent spot.
It should be remembered that the word radiations is used as a
mere matter of convenience. Directly opposite the concave
cathode, there was a green patch of light on the inner surface of
the glass. It was shown that it made no difference where the an-
ode was. This fact becomes useful in carrying on experiments
in connection with Roentgen rays, and it may have a great deal
to do with the solution of the theoretical problems in connection
with electrical discharges in vacuum tubes. In regard to the
three streams shown in Fig. 9, p. 17, it may be stated that only
one occurred at a time in the experiment, for, first one anode
was connected in circuit, and then the next by itself, and then
the third one by itself, while the concave pole was always nega-
tive. Each time the anode was changed, the stream changed,
and connected that pole which was in circuit, 43, but similar
changes made upon the tube with a high vacuum, did not alter
the position of the phosphorescent spot. This and other experi-
ments show that the radiations took place perpendicularly from
the surface of the cathode.
58. SHADOW CAST WITHIN THE DISCHARGE TUBE. This is
illustrated in Fig. u, p. 17, where there is a negative polar disk
at the small end of the egg shaped tube, and a cross near the
large end, the same forming the positive pole. The cross is made
of aluminum. There was a novel action, however, discovered
in addition to the mere casting of a shadow. The glass which
had become phosphorescent except within the shadow, becarn^^^^
after a while, less phosphorescent. Its property to phosphore^H
see became less as proved by removing the cross, which was
arranged to fall down upon tipping the bulb. Immediately, the
part which was within the shadow became brighter than the
rest of the glass, thereby reversing the appearances, by making
a luminous picture of the cross upon only partially phosphore-
scent glass. A remarkable feature is that the glass never recov-
ered its first exhibited power of phosphorescence, neither did
this power entirely become nothing, however many times the
tube was employed. Was the deposit of metal from the cathode
the cause ?
42
$Sa. MECHANICAL MOTION PRODUCED BY RADIATIONS FROM THE
NEGATIVE POLE. It occured to Crookes that the radiations from
the cathode might perhaps cause a wheel to turn around. He
therefore had a minute wheel made by Mr. Gimingham, like an
undershot water wheel, and its axle rested on two rails of glass,
so that it might roll along from one end of the tube to the other.
The vanes were exactly opposite to the plane surface of the
cathode. The molecular stream or radiations, or whatever they
may be, possibly vibrations, from the cathode, were so powerful
mechanically that the wheel was caused to run up hill, the tube
being inclined very slightly. On the principle that action and
reaction are equal, he built another device in which the negative
electrode was movable, and he observed that when the current
was on, the negative elec.trode moved slightly. Upon these
principles he built the well known Crookes radiometer in which
the vanes rotated by reaction of the radiations. The vanes in
this form of radiometer were made of aluminum, and a cup of
hard steel served as the bearing, Fig. 12, p. 17. One side of
eackdisk was coated with a thin scale of mica. The aluminum
disks formed the cathode, while the anode was located at the
top. The operation consisted in connecting the terminals as
stated, so that the vanes were the negative poles and it was
observed that the little wheel rotated. The vacuum was not as
high as that for obtaining phosphorescence. With a low vacuum,
an envelope of violet light existed near the surface of the alum-
inum vanes. Effects were carefully studied by maintaining
connection with the pump. At the pressure of .5 mm. there
was a dark cylinder opposite the aluminum extending to the
glass, and this was the pressure at which the vanes began to
rotate. The dark spaces opposite each vane became larger and
larger in width, until they appeared to be opposed or resisted by
the inner surface of the glass, and then the rotation became
very rapid. He modified this experiment by having vanes en-
tirely of mica, and by having the cathode disconnected electric-
ally from the vanes, Fig. 13, p. 17. A coil of metal near the
vanes served as the cathode. The anode was at a distance in
the top of the tube as in Fig. 12, p. 17. During the electrical
discharge, the wheels rotated by radiations from the coil which
formed the cathode. He made the discovery that when this
coil was heated red hot conveniently by a current from a pri-
mary battery, the vanes also rotated, showing that there is pro-
bably some relation between the radiations from the cathode
and heat rays. The fact remains however, that both kinds of
rays produced rotation, directly or indirectly.
43
59- ACTION OF MAGNET UPON CATHODE RAYS. He had two
tubes, one of which is shown in Fig. 14 and the other in Fig. 15,
on page 17. In the former, the vacuum was so low that a vio-
let stream of light existed between the electrodes. In the other,
the rays were invisible, but were converted into luminosity by
projection at an exceedingly slight angle, upon a phosphores-
cent screen arranged along the length of the tube and inside
thereof. Inasmuch as the whole surface of the cathode in the
latter case radiated parallel and invisible rays, he cut off some
of them by a mica screen having a hole in the centre and lo-
cated near the negative pole, so that only a pencil of invisible
rays could go through the mica screen and act upon the phos-
phorescent screen. In both cases, there was visible a
straight pencil of light. Now notice the effect which took
place upon locating a magnet as indicated in the figures. With
the low vacuum, the pencil was bent out of its course but re-
turned again to the line of its original path. 28. With the
liigh vacuum, the rays were bent but did not return to their or-
iginal direction nor parallel thereto. In the former case, the
magnet acted as upon a very delicate flexible conductor, while
in the latter, it acted, as Crookes said, like the earth upon pro-
jectiles. He modified the latter experiment in order to deter-
mine if the similarity between this phenomenon and gravitation
existed in other respects. He anticipated that if the molecular
resistance to the rays were increased they would be bent more
out of their course like a horizontally projected bullet. He
therefore heated the caustic potash sticks slightly, and in view
of the liberation of molecules of water within the vacuum tube,
the rays, he thought, would be resisted ; and such was the case
to all appearances, for then the pencil of light was bent out of
its course to a greater extent, although the magnetic power re-
mained the same as well as the E. M. F. producing the electric
discharge. He therefore established, apparently, the principle
that the magnetic actions upon cathode rays vary somewhat in
their nature according to the degree of vacuum. In either case,
it may be stated incidentally, that when the magnet was moved
to and fro, the pencils of light waved back and forth.
In the modified form of construction over that shown in Fig.
15, p. 17, he caused a wheel to rotate that was located in the high
vacuum. The vanes of the wheel were so located that the faces
of the same were perpendicular to the direction of the pencil of
the rays radiating from the cathode. When the magnet de-
flected the rays, the wheel ceased rotation.
60. MUTUAL REPULSION OF CATHODE RAYS. If the little mica
44
screen, as shown in Fig. 16, p. 17 has two holes, and if there are
two cathodes instead of one, there will also be two pencils of
light. He performed an experiment involving the latter modi-
fication, and the result was something that could not have been
predicted. The two pencils, as displayed by the long fluores-
cent screen, repelled each other like molecules similarly electri-
fied. The white pencils, it will be noticed, were repelled from
each other and showed their condition when both of the nega-
tive poles were in circuit. The black pencils show the location
of both of the pencils when only one pole is in circuit at a time,
the direction being perpendicular to the plane of the cathode
disc ( 57) at end.
6 1. HEATING AND LIGHTING POWER OF CATHODE RAYS. HEAT
OF PHOSPHORESCENT SPOT. By making the cathode concave as
in Fig. 10, p. 17, and so locating it that the focus of the cathode
rays falls upon some substance, the latter becomes very hot. In
this way Crookes melted wax on the outside of the bulb at the
phosphorescent spot. Further than this, the heat was so great
that it cracked the glass without at first injuring the vacuum ;
next the glass at this point softened, and the air, by its pressure,
rushed into the bulb, forcing a hole through the soft part. He
performed an experiment also which illustrated the intensity of
the heat when the rays were brought to a focus. He used an
unusually large electrode like a concave mirror, and in the fo-
cus, which was near the centre of the bulb, he supported a small
piece of iridio-platinum. At first, with a moderately low E. M. F.,
the metal was made white hot. When a magnet was caused to
approach, the rays were drawn to one side, 59, and the little
piece of metal cooled. He then put in all the coils of an induc-
torium, and allowed the metal not only to become white hot, but
to become so heated that it melted. How little did Prof. Crookes
know about the most important phenomena associated with his
experiment. Although he was so exceedingly enthusiastic and
ingenious in planning his experiments, and in reasoning, yet it
seems almost mysterious that he should have been subjected to
what have become known as X rays, which passed into his body,
and would have photographed portions of his skeleton, and
which would have performed outside of the tube many of the
acts that were noticed within. Seventeen years elapsed between
the time of Crookes on the one hand, and Lenard and Roentgen's
discoveries on the other. Dr. Lodge, F.R S., (The Elect., Lon.,
Jan. 31, '96, p. 438,) and Lenard, in his first paper, attributed to
Hittorf the discovery of the mere existence of cathode rays, but
credited to Crookes the full establishment of their properties,
45
deduction of their principles and formulation of an ingenious
theory.
6 1 a. As an appropriate conclusion to Crookes work, I cannot
do better than to let Lord Kelvin repeat what he said in his
Pres. Addr., Ro. So., Nov. '93, see also The Elect., Lon. Feb. 14,
'96, p. 522, showing that a small portion of the credit is due not
only to Hittorf, 53, but to Varley. " His short paper of 1871,
which, strange to say has lain almost or quite unperceived in the
Proceedings during the 22 years since its publication, contains an
important first instalment of discovery in a new field, the mole-
cular torrent 53, at centre, from the 'negative pole,' the control
of its course by a magnet, 59, its pressure against either end
of a pivoted vane of mica, 59, at end, and the shadow produced
by its interception by a mica screen, 58. Quite independently
of Varley, and not knowing what he had done, Crookes (Roy.
Inst. Proc. t April 4, '79, vol. LX, p. 138. Ro. So. Trans., '74, "On
attractions and repulsions resulting from radiation" Part II, '76,
parts III and IV, '76, part V, '78, part VI, '79) was led to the
same primary discovery, not by accident and not merely by ex-
perimental skill and acuteness of observation." * * * * " He
brought all his work more and more into touch with the kinetic
theory of gases; so much so, that when he discovered the mole-
cular torrent he immediately gave it its true explanation mole-
cules of residual air, or gas or vapor projected at great velocities
(probably, I believe not greater in any case than 2 or 3 kilomet-
ers per second, 6i), by electric repulsion from the negative
electrode. This explanation has been repeatly and strenuously
attacked by many other able investigators, but Crookes has
defended (Presidential address to the Inst. Elect. Eng., 1891.) it,
and thoroughly established it by what I believe is irrefragable
evidence of experiment. Skillful investigations perseveringly
continued brought out more and more wonderful and valuable
results; the non-importance of the position of the positive elect-
rode, 57, near end, the projection of the torrent perpendicul-
arly from the surface of the negative electrode, 57, at end; its
convergence into a focus and divergence thenceforward when
the surface is slightly concave, 47, near beginning; the slight
but perceptible repulsion, 60, between two parallel torrents
due, according to Crookes, to negative electrifications of their
constituent molecules; the change of the direction of the mole-
cular torrent by a neighboring magnet, 59; the tremendous
heating effect of the torrent from a concave electrode when glass,
metal or any ponderable substance is placed in the focus, 61;
the phosphorescence procured on a plate coated with sensitive
paint by a molecular torrent skirting along it, Fig. 15, p. 17; the
brilliant colors turquoise blue, emerald, orange, ruby-red with
which grey, colorless objects, and clear, colorless crystals glow
on their struck faces when lying separately or piled up in a heap
in the course of a molecular torrent, 55; "electrical evapora-
tion" of negatively electrified liquids and solids, 59; (Ito. So.
Proc., June n, '91.) the seemingly red-hot glow, but with no
heat conducted inwards from the surface, of cool solid silver
kept negatively electrified in a vacuum 1/1,000,000 of an atmos-
phere, and thereby caused to rapidly evaporate, 40 and 1390.
This last named result is almost more surprising than the phos-
phorescent glow excited by molecular impacts on bodies not
rendered perceptibly phosphorescent by light, 55, at centre.
Both phenomena will usually be found very telling in respect to
the molecular constitution of matter and origination of thermal
radiation, whether visible as light or not. In the whole train of
Crookes investigations on the radiometer, the viscosity of gases-
at high exhaustion, and the electro-phenomena of high vacuums,
ether seems to have nothing to do except the humble function
of showing to our eye something of what the molecules and
atoms are doing. The same confession of ignorance must be
made with reference to the subject dealt with in the important
researches of Schuster and J. J. Thomson on the passage of
electricity through gases. Even in Thomson's beautiful experi-
ments, showing currents produced by circuital electromagnetic
induction in complete poleless circuits, the presence of mole-
cules of residual gas or vapor seems to be the essential. It seems
certainly true that without the molecules, electricity has no
meaning. But in obedience to logic, I must withdraw one ex-
pression I have used. We must not imagine the "presence
of molecules is the essential." It is certainly an essential. Ether
is certainly also an essential, and certainly has more to do than
merely to telegraph to our eyes to tell us what the molecules
and atoms are about. If the first step towards understanding
the relations between ether and ponderable matter is to be made
it seems to me that the most hopeful foundation for it is know-
ledge derived from experiment on electricity in high vacuum;
and if, as I believe is true there is good reason for hoping to see
this step made, we owe a debt of gratitude to the able and per-
servering workers of the last 40 years who have given us the
knowledge we have; and we may hope for more and more from
some of themselves and from others encouraged by the fruitful-
ness of their labors to persevere in the work."
6i. THOMSON'S EXPERIMENT. VELOCITY OF CATHODE RAYS,
47
The Elect., Lon., Oct. 5, '94, p. 762 ; Phil. Mag., '94. The object
of the experiment of J. J. Thomson was to determine whether
the velocity approached that of light or that of molecules. The
apparatus he employed involved the rotating mirror, which was
fully described in Proc. Royal So., '90, slightly modified. The
rays were caused to produce phosphorescence, while the mirror
was so adjusted that when at rest, the two images on the phos-
phorescent strips appeared in the same rectilinear line. Many
other elements comprised the apparatus. All the steps were
performed carefully and according to the best methods, but the
results are those which in this experiment are of particular in-
terest, for by knowing the velocity of the rays, their nature is
better appreciated and that of the X rays can be better deducted.
The velocity bore a close relation to that of the mean square of
the molecules of gases at temperatures zero C, or in the case of
hydrogen, 1.8 x io 5 cm. per second. As compared with such
a velocity, that of the cathode rays was found to be in the neigh-
borhood of 100 times as great, and this agrees very nearly with
the velocity of a negatively electrified atom of hydrogen ac-
quired under the influence of the potential fall, which occurred
at the cathode. In further evidence of the verity of this state-
ment, he made a rough calculation upon the curve or displace-
ment produced by a magnet upon the rays. 59. He stated :
" The action of a magnetic force in deflecting the rays shows,
assuming that the deflection is due to the action of a magnet on
a moving electrified body, that the velocity of the atom must be
at least of the order we have found."
6i. PERRIN'S EXPERIMENT. CATHODE RAYS CHARGED WITH
NEGATIVE ELECTRICITY. CORRESPONDING POSITIVE CHARGES
PROPAGATED IN THE REVERSE DIRECTION AND PRECIPITATED
UPON THE CATHODE. Comptes Rendus, CXXL, No. 20, p. 1130;
The Elect., Lon., Feb. 14, '96, p. 523. Jean Perrin's object was
to discover whether or not internal " Cathode rays were charged
with negative electricity," That they were had often been as-
sumed by others, namely, Prof. J. J. Thomson, who considered
cathode rays as due to negatively charged matter moving at
high speed. 6i. Again, Prof. Crookes, principally, and
others, showed that they were possessed of mechanical proper-
ties and that they were deflected by a magnet. 59. Perrin
called attention to the above investigations and also alluded to
the theoretical considerations of Goldstein, Hertz and Lenard,
who favored the analogy of cathode rays to light whose phen-
omena are well answered by the accepted theory concerning as-
sumed etherial vibrations, which, in both cases, have rectilinear
4 8
propagation, 57, excite phosphorescence, 54 and 55, and pro-
duce chemical action upon photographic plates. Great ingenuity
was displayed, as might be expected, in the manner in which
Jean Perrin proved the proposition named in the title of this
section, at the Laboratory of the Ecole Normale and also in M.
Pallet's Laboratory. First, therefore, let the elements of the
discharge tube be thoroughly understood. As usual, the disk N
Earth.
,
G|
Electroscope
FIG. 1.
is the cathode, referring to accompanying Fig. i. A, B, c, D, is a
metal cylinder having a small opening at the right hand end
toward the cathode. Concentrically, is a similar cylinder, act-
ing as an electrical screen and having a like opening similarly
located as indicated. It corresponds to and plays the part of
the Faraday cylinder, being connected to earth. The principle
involved in this apparatus was based upon the laws of influence,
which permitted him to ascertain the introduction of electric
charges within a conducting envelope, and to measure such
charges. During the discharge, the cathode rays were propa-
gated from the cathode to and within the cylinder A, B,
c, D, which immediately and invariably became charged with
negative electricity. To prove that the charge was due to
the cathode rays, he deflected them away from the opening in
the protecting cylinder E, F, G, H. The cylinder was not under
these circumstances charged, the rays being outside. He
went further and made some quantitative analysis in a rough
way to begin with. He related : " I may give an idea of the
amount of the charges obtained when I state that with one of
my tubes, at a pressure of .001 m. of mercury, and for a single
interruption of the primary coil, the cylinder ' A, B, c, D, received
sufficient electricity to bring a capacity of 6co c. G. s. units to a
potential of 300 volts. " Upon the principle of the conservation
of energy, he was induced, he said, to search for corresponding
positive charges. " I believe I have found them in the very
region where the cathode rays are generated, and that they
travel in the reverse direction and precipitate themselves on to
the cathode." He verified this corallary by means of a modified
feature of the apparatus shown in Fig. 2. The construction was
49
the same except that there was a diaphragm having a perfora-
tion ft' within the protecting cylinder and opposite the smaller
cylinder exactly as indicated, so that the positive electricity
which had entered through ft could only act on the cylinder A, B,
c, D, by traversing also the hole ft'. " When N was the cathode,
the rays emitted traversed the two apertures at ft and ft' without
E
A
B
r~
a 1 er ff
i
Tl
D
C 1 1
FIG. 2.
any difficulty, and caused the gold leaves of the electroscope to
diverge widely. But when the protecting cylinder was the ca-
thode, the positive flux, which, as was shown by a previous ex-
periment, enters by the aperture ft, did not succeed in separating
the gold leaves, except at very low pressures. If we substitute
an electrometer for the electroscope we shall see that the action
of the positive flux is real, but that it is very small and increases
as the pressure decreases."
He inferred that : " These results, taken as a whole, do not
appear to be easily reconcilable with the theory that the cathode
rays are ultra-violet light. On the contrary, they support the
theory that attributes these rays to radiant matter, 54, near
centre, a theory, which may at present, it seems to me, be enun.
ciated as follows : In the vicinity of the cathode the electric field
is sufficiently strong to tear asunder into ions some of the mole-
cules of the residual gas. The negative ions start off toward
the region where the potential increases, acquire a considerable
velocity, and form cathode rays ; their electric charge, and con-
sequently their mass (at the rate of one gramme equivalent per
100,000 coulombs) is easily measured. The positive ions move
in the reverse direction ; they form a diffused tuft, susceptible
to magnetism, but are not a regular radiation."
6 ic. ZEUGEN. Comptes Rendus, Jan. 27, 1896. In a note
regarding the experiments of Roentgen, called attention to* his
own communications to the Academie des Sciences in February
and August 1886, describing his photographs of Mt. Blanc taken
in the night by the invisible ultra-violet rays. This note is en-
tered as many newspapers reported the photograph to be due
to cathode rays, imagine the intense phosphorescence upon a
screen at the top of the mountain, if such were the case.
62. GOLDSTEIN'S EXPERIMENT. PHOSPHORESCENCE OF PARTIC-
ULAR CHEMICALS BY CATHODE RAYS. Nature, Lon. Feb. 21, '95,
5
p. 4c6. Weid. Ann., No. II, '95. Lithium chloride when acted
upon by cathode rays, phosphoreced to a dark violet color or
heliotrope, which it retained for some time in a sealed tube.
Chlorides generally and other haloid salts of potassium and sod-
ium showed similar effects. The colors were superficial and
could be driven away rapidly either by heating or the action of
moisture.
63. KIRN'S EXPERIMENT. SPECTRUM OF POST PHOSPHORESCENCE
OF DISCHARGE TUBES. Wied. Ann., May, '94. Nature, Lon. June
7, '94, p. 131. Carl Kirn compared the spectra of the phosphore-
scence of a vacuum bulb, during and immediately after
the discharge. The details are as follows: The spectrum of
the after-glow, 54, at end and 22, was found to be continuous.
In this connection, see a plate showing different kinds of spectra,
for example, Ganofs Physics, frontispiece. The spectrum short-
ened from both directions to a band between the wave lengths
of 555 and 495////. The spectrum then continued to grow shorter
and shorter until it disappeared at the line E, which is the posi-
tion of the greatest luminosity of the solar spectrum. For ex-
periments on spectrum, see Fraunhofer in Gilbert's Ann., LVI.
During the discharge, the spectroscope showed a line spectrum
corresponding very closely to those of carbonic acid gas and
nitrogen. Some authorities had suggested that perhaps the
after phosphorescence and the beginning of the incandescence
of a solid body, were the same kind of light, but this experi-
ment shows that such is not the case, unless some relation exists
on the ground that the two phenomena are exactly opposite to
each other, and it confirms similar results obtained by Morrin
and Riess. The result indicates that the nature of the phenom-
enon is not identical in all respects with light produced at a high
temperature.
630. DE METZ'S EXPERIMENT. CHEMICAL ACTION IN THE
INTERIOR OF THE DISCHARGE TUBE. INTERNAL CATHODE RAYS.
L'lnd. Eler., May 10, '96, and Comptes Rendus, about April, '96.
Translated by Louis M. Pignolet. He used a cylindrical dis-
charge tube divided into two halves which fitted together by an
air tight ground joint. In one-half were the anode and the
cathode; in the other half was the holder containing the sensitive
paper or films. The holder was exposed to the direct action of
the cathode rays and was closed by a cover of cardboard or sheet
aluminum. The objects to be photographed were placed
between the cover and the sensitive film or paper. The tube was
connected to a Sprengel pump which maintained its vacuum
during the experiments. In this way, twelve photographs were
taken from which it appeared that cathode rays, like X rays,
penetrate cardboard and aluminum, but are stopped by copper
(1.26 mm.) and platinum (0.32 mm.). Poincare, in a note in the
same publications as the foregoing, criticised the results of the
experiments of De Metz, claiming they did not prove irrefutably
that cathode rays possessed the essential properties of X rays,
for the cathode rays in impinging on the cover of the holder
would generate X rays, 91, which would give the results ob-
tained. Poincare did not deny the fact.
63^. HERTZ'S EXPERIMENT- THE PASSAGE- OF CATHODE RAYS
THROUGH THIN METAL PLATES WITHIN THE DISCHARGE TUBE.
DIFFUSION. Wied. Ann., N. F. 45; 28, 1892. Contributed by re-
quest, by Mr. N. D. C. Hodges of the Hodges Scientific News
Agency, N. Y. Found in records at Astor Library. A piece of
uraniun glass was covered partly on one side (which he calls the
front side) with gold leaf, and on the gold leaf were attached
several pieces of mica. This front side was then exposed to
cathode rays. So long as the exhaustion had not proceeded far,
and the cathode rays rilled the whole tube with a blue cone of
light, only the portion of the uranium glass outside the gold-leaf
screen showed any phosphorescence. But as soon as the exhaus-
tion had progressed far enough, and the light began to disappear,
the genuine cathode rays struck the covered glass, and the phos-
phorescence manifested itself behind the gold-leaf. When the
cathode rays were fully developed, the gold-leaf hardly had any
effect, while the mica cast deep black shadows. The same ex-
periment was tried with silver-leaf, aluminum and alloys of tin,
zinc and copper. Aluminum showed the best results; sheets
which allowed no light to pass, allowing the cathode rays free
passage. The rays after their passage through the metal screens
did not continue their straight course, but seemed to be diffused
much as light is diffused by passing through a cloudy medium.
In this connection reference is made to the work of Goldstein,
who, had noticed also the reflection of " electric " rays. Wied.
Ann., N. F. 15; 246, 1882. In 1893, Goldstein published further
accounts concerning actions in discharge tube. Wied. Ann., vol.
48, p. 785.
DIAGRAM OF LENARD'S APPARATUS, pp. 53 to 69.
CHAPTER VI.
65. LENARD'S EXPERIMENTS. CATHODE RAYS OUTSIDE OF THE
DISCHARGE TUBE. Wied. Ann., Jan., '94, Vol. LVL, p. 225 ; The
Elect., Lon., Mar. 23 and 30, '94, Apr. 6, '94 ; and Elect. Rev.,
Lon., Jan. 24, '96, p. 99. Of more importance in connection
with X rays is the consideration of Lenard's experiments than
any others. The reader must bear in mind that his exhaustive
investigations resulted from his discovery (founded upon a hint
from Hertz) that the cathode rays might be transmitted to the
outside of the generating discharge tube. His interest, there-
fore, in the discovery was so great that his researches extended
to the minutest details. Passing from these introductory re-
marks, the characteristics of the tube that he employed will be
explained first. Reference may now be made to the accom-
panying Fig. A. He employed several different kinds of tubes,
but finally settled upon one of which the essential elements are
shown in the said figures. It was permanently connected to the
pump, 53, so that the pressure within could be varied. "Oppo-
site the cathode, which consisted of a thin disk of aluminum, the
end of the tube was provided with a thick metal cap, having a
perforation, which in turn was closed by a thin aluminum sheet
secured by marine glue in an air-tight manner, and called a
window. The anode was a heavy brass cylinder, shown in sec-
tion, within the discharge tube and surrounding the leading in
wire of the cathode. The anode and the aluminum window
were connected to each other, electrically, and to earth, as well
as two a secondary terminal of an induction coil, whose elec-
trodes were in shunt to those of the discharge tube, in order that
the operator might adjust the sparking distance which rapidly
increased with the exhaustion. The induction coil had a mercury
interrupter.
65. PROPERTIES OF CATHODE RAYS IN OPEN AIR. In all di-
rections around the window upon the outside and in the open
air, a faint bluish glow ( n and 140) extended and vanished at a
distance of 5 cm., as indicated by dotted lines in Fig. B at be-
53
54
ginning of this chapter. The degree of luminosity may be
judged by saying that it was not sufficient to admit of investi-
gation by the ordinary pocket spectroscope. A new window
was void of luminosity ; but with use, bluish gray and green and
yellow spots occurred thereon.
66. PHOSPHORESCENCE BY CATHODE RAYS. Substances which
generally phosphoresced by light and cathode rays in the gen-
erating bulb, 55, also phosphoresced under the influence of the
rays in open air, excepting eosin, gelatin, both phosphorescent
in light, were not so in cathode rays ; so also with solutions of
nuorescein, magdala red, sulphate of quinine and chlorophyll.
Phosphorescence was less if the rays first passed through a tube
of glass or tinfoil lengthwise. The phosphorescent light of the
phosphides of the alkaline group, uranium glass, calcspar and
some other substances, was so great that the luminosity of the
air was invisible by contrast. The maximum distance at which
phosphorescense was discernable in open air was about 8 cm.
The best phosphorescent screen consisted of paper saturated
with pentadecylparatatolylketone. , In order to prepare it, he
laid a sheet of paper upon glass and applied the fused chemical
with a brush. As to the color of the phosphorescence and flu-
orescence of different substances, and as to the degree of lumin-
osity outside of the vacuum tube, they were about the same as
reported by Crookes when located within the discharge tube.
55. Baric and potassic and other double cyanides of platinum,
common flint, glass, chalk and asaron all exhibited the same
property as when exposed to ultra-violet light, that is, fluoresced
or phosphoresced. Sulphide of quinine in the solid state fln-
oresced, but not in solution. Petroleum spread on a piece of
wood fluoresced, and also fluorescent-hydrocarbons generally.
66a. The cathode rays were not easily transmitted by tinfoil
or glass, because the degree of phosphorescence on the screen
was greatly reduced by interposing such sheets. The phos-
phorescense ceased also by deflecting internal cathode rays from
the window by a magnet. For full treatment of the phenomena
of phosphorescence, see Stokes' experiments, described in Phil.
Tram., 1852, Art. " Change of Refrangibility of Light." In
brief, Stokes' theory assumes that such substances have the
power of reducing the refrangibility. Example : Ultra-violet
light, highly refractive, is changed to yellowish green, less re-
frangible, by reflection from uranium glass.
67. THE ALUMINUM WINDOW, A DIFFUSER OF CATHODE RAYS.
63^. The conclusion arrived at by mounting the phosphore-
scent screen in different positions and at different angles as well
55
as by observance of the gaseous luminosity, was that the alum-
inum window scattered the rectilinear parallel cathode rays in
all directions, 57.
68. TRANSMISSION OF EXTERNAL CATHODE RAYS THROUGH
METALS. The phosphorescence was not diminished apparently
by an intervening 1 gold-leaf or silver or aluminum foil, while it
was extinguished by quartz .5 mm. thick which also cut off the
atmospheric glow beyond itself. The leaves and foil did not so
act. The difference of thickness should be borne in mind, as
metal, as thick as the quartz did not transmit. As to other sub-
stances, tissue paper cast a slight shadow, which was darker with
an additional sheet; but the shadow was independent of color
and blackness, 154. Ordinary writing paper was roughly,
proportionally opaque, while the shadow was black with card-
board .3 mm. thick. Glass films as made by blowing glass, cast
faint shadows when .01 mm. thick, He proved that there was
little difference as to the transmitting power of conductors and
dielectrics when thin. Mica and collodion sheets .01 mm. thick
cast scarcely any shadow. The reader may bear in mind the
striking differences between these properties of cathode rays,
and X rays, 135, it being assumed always that the generating
devices are the same; for example, water permitted the cathode
rays (were these simply feeble X rays ?) to be transmitted
only when in very thin layers. Even soap water films which
were only .0012 mm. thick cast shadows, although very faintly.
The shadows of drops of water were black, while water several
feet thick has been traversed by X-rays from a small set of
apparatus. By careful measurements he found that the law of
transmission must be different from that of light, for in the lat-
ter, many substances are opaque although exceedingly thin,
while with cathode rays, the same will traverse all films. Gold-
stein and Crookes reported that thin mica, glass and collodion
films made very dark shadows, 58, within the discharge tube,
whereas Lenard found that outside of the vacuum tube, in open
air, the transparency was greater than according to the earlier
experimenters, but he acknowledged that Crookes and Goldstein
were inconvenienced and limited in the number of observations
because it is so difficult to carry on such experiments within an
hermetically sealed tube. Again, he acknowledged that perhaps
the cathode rays of those experimenters were of a different kind.
The construction shown in the above figures was modified by
using a very thin glass window instead of aluminum, and the
results were the same allowing for the different opacity, to ordin-
ary light, of aluminum and glass.
56
The cathode rays acted upon the sense of smell and taste as
the nose and mouth could detect ozone, 84, at end.
69. PROPAGATION. TURBIDITY OF AIR. Upon studying the
shadows on the phosphorescent screen, it was noticed that the
rays were bent around the edges of the object. Again, when
the object had a slit, diffusion could be noticed by the shape (as
in Crookes Ex., Fig. 15, p. 17,) of the luminous portion of the
phosphorescent screen. In Fig. B, at beginning of this chapter,
the spatter work represents the shape of the luminous portion,
the darker part representing the most luminous surface of the
screen, the latter being held at right angles to the thick plate,
having the slit and opposite the aluminum window. By varying
these experiments, especially by changing the angle of the screen
he found that not the all rays were diffused, but as in the passage
of light through milk, some were transmitted in rectilinear
lines.
70. PHOTOGRAPHIC ACTION. He performed with sensitive
silver compound papers, an experiment somewhat similar to
those with phosphorescent bodies and also others. Behind a
rather thick opaque plate the chemical film was not acted upon,
but the rate of blackening near the aluminum window without
obstruction of intermediate bodies was about the same as that
with befogged sunlight. The former, moreover, was acted
upon at a much greater distance than that at which phosphor-
escence was exhibited and beyond the atmospheric luminosity.
By means of shadow pictures or sciagraphs, he compared the
shadows produced by the external cathode rays with those which
would have been obtained by light. Referring to Fig. C , be-
ginning of this chapter, the sensitive plate was half covered with
a plate of quartz. Q, and half with a plate of aluminum, A ' over-
lapping the quartz. With light, the shadows would have ap-
peared as in said figure, that is, one-half black as produced by
aluminum, a quarter rather light as produced by quartz, and the
other quarter bright, or a similar arrangement, according to
whether the negative or the positive photograph is considered;
but with the cathode rays, the appearance of the developed
plate was as in Fig. D., beginning of this chapter. The quartz
cast the black shadow, while the aluminum, the lighter one.
Furthermore, the luminosity of the air produced a variable light
on the other quarters. A similar appearance was produced by
casting shadows of such plates upon the phosphorescent screen ;
but, of course, the picture was not a permanent one. The pho-
tographic plate served to accumulate the power, for the card-
board which cast a faint shadow upon the phosphorescent
57
screen, showed a black shadow upon the photographic paper by
sufficiently long exposure. At the same time, strips of thin
metal were placed side by side between the chemical paper and
the cardboard, and they showed different degrees of shading.
The cardboard was quite thick, being .3 mm. Prof. Slaby (see
Elect. Rev., Lon., Feb. 7, '96), after Rontgen's discovery, pro-
duced sciagraphs of the bones of the hand at the window of the
Lenard tube. Lenard doubted whether the cathode rays pro-
duced direct chemical action. Iodine paper became bluish, but
he could not obtain other chemical effects usually produced by
light, and other agencies, for example, oxygen and hydrogen
mixed together in the proportion to form water, and which were
in their nascent state, and which were located in a soap-bubble,
did not explode or ignite. No effect was produced upon carbon
bi-sulphide nor hydrogen-sulphide, although the exposure was
very long. Ammonia was not formed when the rays acted
upon a mixture of three parts hydrogen and one part nitrogen,
as to volume. He thought that he noticed a small expansion
of air, hydrogen and carbonic acid separately located in a vessel
having a cipillary tube and water to indicate the expansion.
He attributed the slight expansion to an indirect action, al-
though very slight, caused by heat produced by the cathode
rays, 27, and yet neither the thermopile nor the thermometer
showed any calorific effects although the thermopile responded
to the flame of a candle 50 cm. distant.
71. CATHODE RAYS AND ELECTRIC FORCES DISTINGUISHED. The
earth connection heretofore mentioned with the aluminum win-
dow was for the purpose of dispensing with sparking, but even
then the approach of another conductor connected to earth
would cause some sparking. Sparks could be drawn when the
cathode rays were deflected from the aluminum window by a
magnet. Fig. E, at beginning of chapter. He argued that the
rays and the electric forces of the spark are non-identical. He
was not satisfied with this as an absolute proof, and he instituted
others. He enclosed the whole generator in a large metal box.
In the observation space, that is, around and near the window,
he located another box, having an aluminum front facing the
window. See Fig. E, at beginning of chapter. It was within
this second box that he took the sciagraph shown in Fig. D, at
beginning of chapter. It is important to notice that sparks could
not be drawn at points within the said second box, shown at the
left, even by a metallic point shown projecting thereinto. No
spark occured whatever, not even from the aluminum front.
Sparking occurred when the pointed wire was extended to a con-
58
siderable distance outside of the back of the small box, but it
was remarked that the electric force did not enter through the
front wall but was introduced "from behind into the box, by the
insulation of the wire." No one can, therefore, enter the objec-
tion that the cathode rays experimented with, were generated
from the aluminum window as a cathode. They came from the
cathode referred to entirely within the vacuum tube. Prof. J. J.
Thomson, F. R. S., had at an early date conjectured that cathode
rays did not pass through thin films of metal, but that these
films acted as intermediate cathodes themselves. See his book
on ""Recent Researches" p. 26, also The Elect., Lon. March 23, '94,
p. 573, in an article by Prof. Fitzgerald, who names that citation.
72. CATHODE RAYS PROPAGATED, BUT NOT GENERATED IN A
HIGH VACUUM. The proposition was proved by having two
tubes, one called the generating tube and one the observation
tube, the former being like that shown in Fig. A, at beginning
of chapter, which is partly repeated in Fig. F, at beginning of
chapter, combined with the observation tube, which contains the
two electrodes for casual use; but the one on the right is a disk
extending nearly throughout the cross sectional area, and hav-
ing a small central opening. Although both tubes were con-
nected to the air pump, yet, by means of stop-cocks, the vacuum
in one tube could be maintained at a maximum degree for hours,
while the other was at a minimum. The first experiment was
performed with a vacuum, about as high as that employed in
Crookes' phosphorescent experiments, 53. There was a patch
of green light, 57, at the extreme left end of the observation
tube and the glass was green at the right, 54, and a little to
the left of the perforated disk electrode a. The other electrode
of this tube was located at the upper left and lettered k.
720. The magnet deflected the rays in the observing tube as in-
dicated by the partial extinction of the phosphorescent patch.
He noticed that with the rarefied atmosphere the amount of
turbidity was enormously reduced, or in other words, that the rays
were propagated more nearly in rectilinear lines. All the ex-
periments on the cathode rays, in this observing tube, were of
about the same nature as those which could be produced in
the discharge tube.
72^. The principal experiment consisted in exhausting the
observing tube to such a degree that cathode rays could not be
generated therein. The vacuum was so perfect that when used
as a discharge tube all phosphorescence gradually died away
until it disappeared, and no current passed (25) except on the
outside surface of the glass. The coil was so large, electrically,
FROM SCIAGRAPH OF CAT'S LEG, BY PROF. WILLIAM F. MAGIE<
Copyright, 1896, by William Beverly Harison, pub. of X-ray pictures,
59 Fifth Ave., New York City.
6o
that the length of the spark between spheres was 15 cm. Upon
charging the right hand tube and generating cathode rays, it
was determined by means of magnetic deflection, phosphor-
escence and other effects, that the cathode rays traversed the
highest possible vacuum ( 19, near end, where energy must
have passed through the high vacuum to produce luminosity in
the inner bulb). The external and internal rays were certainly
different forms of energy. Inasmuch as he noticed that rare-
fied air was less turbid and less absorptive than air at ordinary
pressures, it occurred to him to make a very long tube, namely,
i m, or a little over 3 feet. He employed very severe steps for
obtaining an exceedingly high vacuum, the operation occupying
several days. The pump used was a Toepler-Hagen, while a
Geissler pump was employed separately for the discharge tube.
The pencil of cathode rays traversed the whole length of the
long tube. See a portion of the apparatus in Fig. G, at begin-
ning of this chapter. One disk was of metal and perforated with
a pin hole and the other was a phosphorescent screen, so that
when the cathode pencil passed through the hole in the plate a
patch was seen upon the phosphorescent screen. The phosphor-
escent spot was always, no matter what the relative distances of
the disks were from each other, and from the end of the tube r
substantially the same as it would have been by calculation as-
suming that there was no turbidity effect. The patches, in each
instance, were a little smaller in diameter than the calculated
ones. For example with one measurement, at certain distances,
the actual diameter of the patch was 2.5 mm., while the calcu-
lated diameter was 2.9 mm. In his experiments with light un-
der the same conditions, the luminous spots were also a little
smaller than the calculated or geometrical. The disks had iron
shoes and were moved to different positions by a magnet. He
concluded, therefore, that in what may be called a perfect va-
cuum, light and cathode rays have a common medium of propa-
gation, namely, the assumed ether. Prof. Fitzgerald, in The
Elect. Lon , Mar. 23, '94, does not agree broadly with him in this;
neither does he contradict him. He argues rather on the point
that the cathode rays and light rays are not identical, but Len-
ard does not affirm this, because the magnet will attract the
former and not the other. Prof. Fitzgerald admits this and calls
to mind that even in a vacuum, as obtained by Lenard, there
were still ten thousand million molecules per cu. mm. and there-
fore he thinks it is better to look to matter rather than ether as
the medium of propagation of cathode rays. 6i. On the
other hand, Lenard agrees with certain other predecessors,
6i
Wiedemann, Hertz and Goldstein, in favor of cathode rays being
etheric phenomena. See Wied. Ann., IX., p. 159, 'So ; X., p. 251,
'80, XII., p. 264, '81 ; XIX., p. 816, '83 ; XX., p. 781, '83. The
vacuum with which Lenard operated, was .00002 mm pressure,
obtained by cooling down the mercury to minus 21 C. This
vacuum was so high that all attempts to prove the presence of
matter failed. Neither did the exceedingly high vacuum deaden
the cathode rays. On the other hand, as noted, they were as-
sisted rather than hindered. 135.
73. CATHODE RAYS. PHENOMENA IN DIFFERENT GASES. The
apparatus consisted of an observing tube having a tubular gas
inlet and outlet both in one end and arranged in line with the
cathode of the discharge tube. See construction in Fig. H, at be-
ginning of this chapter, the tube being about 40 cm. long 'and 3
cm. in diameter. He was very careful in every case to chemically
purify and dry the particular gas. He omitted the perforated disk
and provided an opaque strip of the phosphorescent screen on the
side toward the window and made his observations from the
other side, the object of the experiment being particularly to
test the transmission of cathode rays in different gases. With
any particular gas, he moved the phosphorescent screen along
by means of a magnet until the shadow on the screen became
invisible. It is evident that the distances of the screen from
the window for different gases would indicate the relative trans-
mitting powers. He also modified the experiment by varying
the density of the gases, hydrogen being taken as i as usual,
nitrogen 14, and so on. The transmitting power of hydrogen
was nearly five times as great as that of nitrogen, air, oxygen
and carbonic acid gas, which did not much differ. 10 and 18.
Sulphurous acid was a very weak transmitter. All the gases
became luminous near the window as in air. 65. The colors
were all about the same as far as distinguishable, n, which
was difficult in view of the brightness of the phosphorescence
on the glass. It was a universal rule, that when the density de-
creased, the transmitting power increased. In high vacua, in
all gases, the rays went through the space in rectilinear lines in
all directions from the window, and generally it made no differ-
ence what gas was employed provided the vacuum was as high
as hundredths of a millimetre. At this pressure all gases acted
the same. To be sure, the phosphorescence did not occur at
this high vacuum at a great distance as might be expected, but
it should be'remembered that the intensity of the rays varied as
the square of the distance, and, therefore, at very great distances,
the action was very weak.
62
74- CAUSE OF LUMINOSITY OF GAS OUTSIDE THE DISCHARGE
TUBE. At ordinary pressures, in the cases of hydrogen and air,
as has been noted, the gas became luminous in the observing
tube, the effect being, of course, the same as entering open air,
represented in Fig. A, beginning of this chapter. In order to
determine the luminosity at less pressures, the gas, of which-
ever kind, was enclosed in a rather long observing tube and
only at rather high vacua did the bluish and sometimes reddish
gaseous luminosity disappear. Upon grasping the tube with
the hand or approaching any conductor connected to earth, of
large capacity, the column stopped at that point so that the re-
mainder of the tube, beyond the hand, measured from the dis-
charge, was dark. The phosphorescence on the glass wall of
the tube produced by the cathode rays was not influenced in
any way by outside conductors, such as the hand. Cathode rays
themselves were not stopped apparently by the hand, because
the phosphorescent screen and glass, located beyond the hand,
became luminous. He concluded, therefore, that the glowing
of the gas had no close connection with the cathode rays. He
proved this also by deflecting the cathode rays in the discharge
tube from a certain space, and yet the gaseous luminosity re-
mained. As an exception, the cathode rays sometimes appeared
to be closely associated with the light column. He attributed
the luminosity of the gas in general, at low pressures, not to the
cathode rays, but directly to the electric current or some kind of
electric force, n and 14, which, as already remarked, per-
mitted sparks to be drawn from the aluminum window and sur-
rounding points.
The negative glow light in Geissler tubes, 30, is also to be
regarded as gas illuminated by cathode rays. (Compare Hertz,
Wied. Ann., XIX., p. 807, '83.) Between that phenomenon and
the glow observed here and attributed to irradiation, there ex-
ists a correspondence, inasmuch as in both cases the light dis-
appears at high exhaustions, 53, appears fainter and larger
when the pressure increases, 54, and then becomes brighter
and smaller, 54. But, whereas, the glow in the Geissler tube
has become very bright and small at 0.5 mm. pressure, the gas
in our experiment remains much darker up to 760 mm. pressure,
and yet the illuminated spot is much larger. This difference
cannot, therefore, be attributed to an inferior intensity of the
rays here used. But it will be explained, 76, as soon as we
can show that at higher pressures cathode rays of a different
kind are produced, which are much more strongly absorbed by
USE OF STOPS IN SCIAGRAPHY. (PERCH.) io7a, p. 101,
By Leeds and Stokes.
64
gases than the rays investigated hitherto and produced at very
low pressures.
Fig. I, p. 52, illustrates the apparatus by which he studied the
rectilinear propagation and whereby he found that it was recti-
linear only in a very high vacuum. In the figure, the gas is at
ordinary pressure, and it will be noticed that the turbidity of
the same is indicated by the curved lines while the dotted lines
show the volume that would be occupied by light or other rec-
tilinear rays, unaccompanied by any kind of diffusion. In the
observing tube, there was a disc having a central hole at a.
Beyond this disc, measured from the aluminum window, was a
fluorescent screen which, as well as the perforated disc, could
be moved to different distances by means of a magnet acting on
a little iron base. It is evident that upon moving the fluor-
escent screen to different distances, the diameter of the lumin-
ous patch would be a measure of the amount of turbidity. The
curved lines intersecting the peripheries of the luminous spots
indicate, therefore, the field of the cathode rays, so that said
field would appear like a kind of curved cone if the same were
visible. Although hydrogen is the least turbid gas, yet the
phosphorescent patches were all larger except with a high va-
cuum than they could have been with rectilinear propagation.
An additional characteristic of the phosphorescent spot, was its
being made up of a central bright spot and a halo lessluminous,
appearing like some of the pictures of a nebula, see Fig. I', p. 52,
the darker or centre indicating the brighter portion. In a per-
fect vacuum the halo did not exist. He performed a similar
experiment with ordinary light. No halo occurred on a paper
screen which was used instead of the phosphorescent screen,
but upon introducing a glass trough of dilute milk between the
window and the perforated disc, or between the disc and the
paper screen, nuclei and halos were obtained, illustrating a case
of the effect of a turbid fluid upon light, and assisting in prov-
ing that gases act as a turbid medium to cathode rays as milk
and similar substances do to light ; also in other gases than hy-
drogen, and by the use of cathode rays, nuclei and halos were
not obtained at high exhaustion, all the gases becoming limpid.
Taking into account pressure and density, all gases behaved the
same as to the power of transmission when they were of the
same density, without any regard whatever to their chemical
nature. Density alone determined the matter, according to
Lenard.
75. CATHODE RAYS OF DIFFERENT KINDS ARE VARIABLY DIF-
FUSED. He discovered the remarkable property, contrary to his
65
expectation, that if the rays are generated at high pressures,
they are capable of more diffusion than when generated at lower
pressures. This can be easily proved by any one, for it will be
noticed that upon increasing the pressure in the discharge tubes
the spots on the phosphorescent screen will not only grow darker
but larger and more indefinite as to the nucleus and halo. He
called attention to the agreement with Hertz, who also found
that there were two different kinds of rays, see Wied. Ann., XIX,
p. 816, '83, also see Hertz's experiment. Lenard also pointed
out the analogue in respect to light, which, when of short wave
length, is more diffused in certain turbid media than that of
greater wave length. Although Lenard held that his experi-
ment proved that cathode rays were phenomena in some way
connected with the ether, yet he pointed out an important differ-
ence in connection with the property of deflection of the rays by
the molecules even of elementary gases like hydrogen, produc-
ing diffusion of the rays, which accordingly may be considered
as behaving like light in passing through, not gases, but vapors,
liquids and dust. In the case of the cathode rays the molecules
of a gas acted as a turbid medium, but in the case of light, tur-
bidity is only exhibited by vapors or certain liquids, as so elo-
quently explained by Tyndall, in ''Fragments of Science," 1871,
where it is shown that aggregation of molecules, like vapors or
dust in the presence of light, make themselves known by color
and diffusion, whereas the substances in a molecular or atomic
state do not serve to show the presence of rays of light.
76. LAW OF PROPAGATION. Lenard recognized continually
that there were two kinds of cathode rays. One of them may
have been X-rays without his knowing it. In the latter part of
'95, he made some experiments especially of a quantitative na-
ture as to the principle of absorption of the rays by gases. By
mathematical analysis, based upon experiments, he arrived at
the principle that the absorptivity of a gas is proportional to its
pressure, or what is the same thing, to its density, or as to an-
other way of stating the law, '* the same mass of gas absorbs at
all pressures the same quantity of cathode rays." See Elect.
Jtev., Lon., as cited, p. 100.
77. CHARGED BODIES DISCHARGED BY CATHODE RAYS. An
insulated metallic plate was charged first with positive elec-
tricity and in another experiment with negative electricity. In
each instance, the plate was discharged rapidly by the cathode
rays as indicated by the electroscope, and the same held true
when a wire cage in contact with the aluminum window, sur-
rounded the electroscope and the metallic plate. The effect was
66
stopped by cutting off the cathode rays by quartz .5mm. thick.
The discharge took place, however, through aluminum foil. A
magnet was made to deflect the internal cathode rays, where-
upon the discharge did not take place, all showing that the dis-
charge of the insulated plate was directly due to those rays. A
remarkable occurrence was the accomplishment of the discharge
at a much greater distance than that at which phosphorescence was ex-
hibited. See also Roentgen's experiment who suggested that
Lenard had to do with X-rays in this experiment, but thought
they were cathode rays. The maximum distance for the dis-
charge was about 30 cm. measured normally to the aluminum
window. He caused a discharge of a plate also in rarefied air.
He admitted that the experiments were not carried far enough
to know whether the effect was due to the action of the cathode
rays upon the surface of the window, or upon the surrounding
air, or upon the plate. The author could not find in Lenard's
paper any positive or negative proof that he had actually de-
flected the external cathode rays by a magnet while passing
through air or gas at ordinary pressure. He had deflected them
while passing through a very high vacuum in the observing
tube. Dr. Lodge, who briefly reviewed Lenard's experiments,
expressed the same opinion. See The Elect., Lon., Jan. 31, '96,
p. 439. For theoretical considerations of the electric nature of
light, the discharge law in the photo-electric phenomena, the
simple validity of the discharge law, the occurrence of interfer-
ence surfaces in the blue cathode light, the cathode rays in the
axis of symetry, the necessary degrees of longitudinal electric
waves, the frequency of the cathode rays, and proof of longitu-
dinal character of cathode rays, see Jaumann in The Elect., Lon.,
Mar. 6, '96 ; translated from Wied. Ann., 571, pp. 147 to 184, '96,
and succeeding numbers of The Elect., Lon., which were freely
discussed in foreign literature contemporaneously,
78. DE KOWALSKIE'S EXPERIMENT. SOURCE, PROPAGATION
AND DIRECTION OF CATHODE RAYS. Acad. Set. Paris, Jan. 14,
'95; So. Fran.Phys. Jan. '95; Nature, Lon. Jan. 24, '95; Feb. 21, '95.
The conclusions he arrived at are, i. The production of the
cathode rays does not depend on the discharge from metallic
electrodes across a rarefied gas, nor is their production con-
nected with the disintegration of metallic electrodes. 2. They
are produced chiefly where the primary illumination attains
suitable intensity, that is, where the density of the current lines
is very considerable. 3. Their direction of propagation is that
of the current lines at the place where the rays are produced,
from the negative to the positive poles. They are propagated
67
in the opposite direction to that in which the positive luminosity
is supposed to flow. 43. He employed a Goldstein tube reduced
at the centre. 41. It was found that the cathode rays are
formed not only at the negative electrode, but also at the con-
striction, directly opposite the cathode. De Kowalskie carried
on further experiments in this line in order to be satisfied with
the principles named above, which he formulated. In one tube,
he was able to produce cathode rays at either end of the capil-
lary tube forming the constricted part of a long vacuum tube.
No electrodes were employed. The tube was merely placed
near a discharger through which "Tesla currents " were passed ?
He seems to have been working with X-rays without knowing
it ; for his results agree with those of Roentgen and later experi-
menters that the source of X-rays is the surface of a substance
where it is struck by cathode rays. The statements were about
as definite as could be expected at that date.
V
f
HAND, BY OLIVER B. SHALLENBERGER, TAKEN WITH FOCUS-TUBE.
137, p. 136.
CHAPTER VII.
79. ROENTGEN'S EXPERIMENTS. X-RAYS, AND A NEW ART.
Wurz. Physik. Med. Gesell. Jan. '95 ; Nature, Lon. Jan. '96 ; The
Elect. Lon. April 24, 96; Sitz. Wurz. Physk. Inst. D. Uni. Mar.
9, 96. UNINFLUENCED BY A MAGNET IN OPEN AIR. Although
Lenard recognized several kinds of cathode rays, which differed
as to penetrating and phosphorescing power, yet he always held,
or inferred at least that they were deflected by a magnet, out-
side, as well as inside, (proved 720) of the discharge tube. 59.
Prof. Wilhelm Konrad Roentgen subjected his newly discovered
rays to the action of very strong magnetic fields in the open air,
but no deviation was detected. This is the characteristic which
more than anything else has served to distinguish X-rays from
cathode rays. This property has been confirmed by others. He
employed the principle of magnetic attraction of internal cathode
59, rays to shift the phosphorescent spot, for then he noticed
that the source of X-rays fluctuated also.
80. SOURCE OF X-RAYS MAY BE AT POINTS WITHIN THE
VACUUM SPACE. In one case, he employed a Lenard tube, and
found that the X-rays were generated from the window which
was in the path of the cathode rays. 67. Different bodies within
the discharge tube were found to have different quantitive
powers of radiating X-rays when struck by the cathode rays.
He stated " If for example, we let the cathode rays fall on a
plate, one half consisting of a 0.3 mm. sheet of platinum and
the other half a i mm. sheet of aluminum, the pin hole photo-
graph of this double plate will show that the sheet of platinum
emits a far greater number of X-rays than does the aluminum,
this remark applying in every case to the side upon which the
cathode rays impinge." On the reverse side, however, of the
platinum, no rays were emitt jJ:/)but a large amount was radiated
from the reverse side of the' "aluminum. 67. He admitted
that the explanation was simple ; but, at the same time, he
pointed out that this, together with other experiments, showed
that platinum is the best for generating the most powerful X-rays.
69
K,
One form with which he experimented
! \ \ \S r
A j 4Jr is illustrated in Fig. J, in principle, be-
ing described as a bulb in which a con-
cave cathode was opposite a sheet of
platinum, placed at an angle of 45 to
the axis of the curved cathode, and at
the focus thereof.
81. REFLECTION OF X-RAYS. He emphasized the knowledge
that there is a certain kind and a certain amount of reflection,
such as that produced upon light and, as pointed out by Lenard,
upon cathode rays, by certain turbid media. The following quo-
tation sets forth the exact experiment to show slight reflection
at metal surfaces. " I exposed a plate, protected by a black
paper sheet 1 to the X rays ( e. g. from bulb J) so that the glass
side 2 lay next to the discharge tube. The sensitive film was
partly covered with star-shaped pieces (4 slightly displaced in
the Fig.) of platinum, lead, zinc and aluminum. On the devel-
oped negative the star-shaped impressions showed dark (com-
paratively) under platinum, lead and more markedly, under zinc;
the aluminum gave no image. It seems, therefore, that the
former three metals can reflect the X-rays; as, however, another
explanation is possible, I repeated the experiment with only this
difference, that a film of thin aluminum foil was interposed be-
tween the sensitive film and the metal stars. Such an aluminum
plate is opaque to the ultra-violet rays, but transparent to X-rays.
In the result the images appeared as before, this pointing still
to the existence of reflection at metal surfaces."
82. PENETRATING POWER. The transmitted energy was tested
both by a fluorescent screen and by a sensitive photographic
plate. Either one was acted upon by the rays after transmission
through what have ordinarily been called opaque objects. 68,
for example, 1000 pages of a book. As in Lenard's results, so in
Roentgen's, the color of the object had no effect, even when the
material was black, g 68, near beginning. A single thickness
of tinfoil scarcely cast a shadow on the screen. 660. The same
was true with reference to a pine board 2 or 3 cm. thick. They
passed also through aluminum 15 mm. thick. 63$. Glass was com-
paratively opaque, 66<z, as compared with its power of trans-
mitting light, but nevertheless it must be remembered that the
rays passed through considerable thickness of glass. The tissues
of the body, water 68, near centre, and certain other liquids
and gases were found exceedingly permeable 67. Fluorescence
could be detected through platinum 2 mm. thick and lead 1.5
mm. thick. Through air the screen was illuminated at a max-
7 1
imum distance of i m. A rod of wood painted with white lead
cast a great deal more shadow than without the paint, and in
general, bones, salts of the metals, whether solid or in solution,
metals themselves and minerals generally were among the most
resisting materials. 155. The experiments were performed
in a dark room by excluding the luminosity of the tube by a
thick cloth or card board entirely surrounding the tube. He
performed the wonderful experiment, so often since repeated,
of holding the hand between the screen of barium platino cyan-
nide and the discharge tube, and beholding the shadow picture
of the bones. This was the accidental step which initiated the
new department of photography, and which gave to the whole
science of electric discharge, a new interest among scientists and
electricians and which thoroughly awakened popular interest.
The whole world concedes to him the honor of being tfie origin-
ator of the new art. In view of sciagraphs of the bones of the
hand upon the screen, it occurred to him in view also of Lenard's
experiments, on the photographic plate, to produce a permanent
picture of the skeleton of the hand with the flesh faintly out-
lined. 84. The accompanying half tone illustration, page 37,
was made by the Elect. Eng N. Y. (June 3, '96) by permission,
and it represents the Edison X-ray exhibit at the New York
Electrical Exposition of the Electric Light Association, 1896.
Thousands of people, through the beneficence of Dr. Edison,
were permitted to see the shadows of their bones surrounded by
living flesh. The screen was made of calcic tungstate. The
hand and arm were placed behind and viewed from the front.
132, near beginning.
83. PENETRATING POWER AND DENSITY OF SUBSTANCES. Al-
though he found that there was some general relation between
the thickness of materials and the penetrating power, yet he
was satisfied that the variation of the power did not bear a di-
rect relation to the density, (referring to solids) especially as he
noticed a peculiar result when shadows were cast by Iceland
spar, glass, aluminum and quartz of equal thickness. The Ice-
land spar cast the least shadow upon suitable fluorescent or pho-
tographic plate. The increased thickness of any one substance
increased the darkness of the shadow, as exhibited by tinfoil in
layers forming steps. Other metals, namely platinum, lead,
zinc and aluminum foil were similarly arranged and a table of
the results recorded. 63^.
72
THICKNESS. RELATIVE THICKNESS. DENSITY.
Platinum 018 mm. i 21.5
Lead 050 " 3 11.3
Zinc 100 " 6 7.1
Aluminum 3. 500 " 200 2.6
He concluded from these data that the permeability increased
much more rapidly than the thickness decreased.
84. FLUORESCENCE AND CHEMICAL ACTION. 70 and 63^.
Among the substances that fluoresced were barium platino cy-
anide, calcium sulphide, uranium glass, Iceland spar and rock
salt. In producing sciagraphs on the photographic plates, he
found it entirely unnecessary to remove the usual ebonite cover,,
which, although black, and so opaque to light, produced scarcely
any resistance to the rays. The sensitive plate, even when pro-
tected in a box, could not be kept near a discharge tube, for he
noticed that it became clouded. He was not sure whether the
effect iipon the sensitive plate was directly due to the X-rays or
to a secondary action, namely, the fluorescent light which must
have been produced upon the glass plate having the film, it be-
ing well known that light of fluorescence possesses chemical
power. He called attention to the fact that inasmuch as fluor-
escent light which can be reflected, refracted, pblarized, etc.,
was produced by the rays ; therefore, all the X-rays which fell
upon a body did not leave it as such. 67. No effect was pro-
duced upon the retina of the eye although he temporarily con-
cluded that the rays must have struck the retina in view of the
great permeability of animal tissue and liquids. 68, at end.
Conclusions of this kind not based on experiment, are never re-
liable, even when offered by very high authorities. Again the
rays were weak. Roentgen himself admitted that the salts of
metals in solution ( 82, near centre) rendered the latter rather
opaque. The eye ball is continually moistened with the solu-
tion of common salt. Further than this, Mr. Pignolet noticed
in Comptes Rendus, Feb. 24, '96, an account of an experiment of
Darien and de Rochas. In anatomy it is common to experiment
on fresh pig's eyes in order to make comparisons with human
eyes. The above named Frenchmen submitted the former to
X-rays. The eyes were but slightly -permeable thereto.
85. NON-REFRACTION AND BUT LITTLE REFLECTION OF X-
RAYS. He employed a very powerful refracting prism made of
mica and containing carbon bi-sulphide and water. The same
prism refracted light but did not refract X-rays. No one would
think of making prisms for examining light, of ebonite or alu-
minum, but he made such a prism for testing X-rays. But if
74
there were any refraction he concluded that the refractive index
could not have been more than 1.05, which may be considered
as a proof that the rays cannot be refracted. He tried heavier
metals, but the difficulty of arriving- at any satisfactory results
was due to the resistance of such metals to the transmission of
the rays. Among other tests was one consisting in passing the
rays through layers of powdered materials through which the
rays were transmitted in the same quantity as through the same
substances not powdered. It is well known that light passed
into powdered transparent materials, is enormously cut off,
deviated, diffused, refracted etc., in view of the innumerable
small surfaces of the particles. Hence he concluded that there
was little if anything in the nature of refraction or reflection of
X-rays. 146. The powdered materials employed were rock
salt, and fine electrolytic and zinc dust. The shadows, both on
the screen and as recorded on the photographic plate were of
substantially the same shade as given by the same materials of
the same thickness in the coherent state. One of the most usual
ways of testing refraction of light is by means of a lens. X-rays
could not be brought to a focus with the lens of what ever ma-
terial it was made. Among the substances tried were ebonite
and glass. As expected, therefore, the sciagraph of a round rod
was darker in the middle than at the edges; and a hollow cylin-
der filled with a more transparent liquid showed the centre por-
tion brighter than its edges. If one considers this observation
in connection with others, namely the transparency of powders,
and the state of the surface not being effective in altering the
passage of the X-rays through a body, it leads to the probable
conclusion that regular reflection does not exist, but that bodies
behave to the X-rays as turbid media to light, 69.
86. VELOCITY OF X-RAYS IN DIFFERENT BODIES, p. 46.
Although he performed no direct experiment in this direction
yet he inferred in view of the absence of refraction at the sur-
faces of different media, that the rays travel with equal velocities
in all bodies.
87. DOUBLE REFRACTION AND POLARIZATION. Neither could
he detect any action upon the rays by way of refraction by Ice-
land spar at whatever angle the crystal was placed. As to this
property of light see Huygen's Works of 1690 and Malus' Works
of 1 8 10. Quarts also gave negative results. Prof. Mayer of
Stevens Institute submitted to Set., Mar. 27, '96, the report of a
crucial test for showing the non-polarization of X-rays. On
six discs of glass, 0.15 mm. thick and 25 mm. in diameter, were
placed very thin plates of Herapath's iodo-sulphate of quinine.
75
The axes of these crystals crossed one another at various angles.
When the axes of two plates were crossed at right angles no light
was transmitted ; the overlapping surfaces of the plates appear-
ing black. If the Roentgen rays be polarizable, the Herapath
crystals, crossed at right angles, should act as lead and not allow
any of the Roentgen rays to be transmitted. Prof. Mayer is
well known as exceedingly expert in connection with minute
measurements and in the manipulation of scientific experiments.
Dr. Morton, Pres. Stevens Inst., attested the results as an abso-
lute demonstration that X-rays are incapable of polarization.
Stevens Indicator, Jan., '96.
88. THE PROPAGATION OF X-RAYS RECTILINEAR. There would
be no difficulty in producing photographs of the bones of the
hand with the rays of light, if it were not for the tremendous
amount of reflection and refraction causing so much diffusion
that no sharply defined shadow of the bones would be produced.
By means of a powerful lens and a funnel pointed into a dark
room, the author noticed that the condensed light thereby ob-
tained when passed through the hand, and when the incident
rays were parallel, came out so diffused that one would think
that the light went through bones as easily as any part of the
hand. An experiment of this kind serves to emphasize that the
success of sciagraphy by X-rays is due not only to the great
penetrating power, but to practically no refraction nor reflec-
tion. In view of the sharp shadows cast of objects even when
located in vegetable or animal media, Roentgen was justified in
giving the name of ray to the energy. He tested the sharpness
of the shadow by making sciagraphs and fluorescent pictures
not only of the bones of the hand, but of a wire wound upon a
bobbin, of a set of weights in a box, of a compass, card and
needle, conveniently closed in a metal case, and of the elements
of a non-homogeneous metal. To prove the rectilinear propa-
gation further, he received the image of the discharge tube upon
a photographic plate by means of a pinhole camera. The pic-
ture was faint but unmistakable.
89. INTERFERENCE. The rays of light may be caused to inter-
fere with each other. See Newton's Principia, Vol, III. ; Young's
Works, Vol. I. Theory points out that waves of ether of two
pencils of light, when caused to be propagated at certain relative
phases partially or wholly neutralize or strengthen each other.
Roentgen could obtain no interference effects of the X-rays, but
did not conclude that the interference property was absent. He
was not satisfied with the intensity of the rays and therefore
could not test the matter severely.
7 6
90. ELECTRIFIED BODIES DISCHARGED BY X RAYS. p. 47.
After Roentgen's first announcement, others, and probably J. J.
Thomson as the first, found that the X rays would discharge
both negatively and positively electrified bodies. Roentgen, in
his second announcement, stated that he had already made such
a discovery, but had not carried the investigation far enough to
report satisfactorily on the details. At last he put forth an ac-
count of the whole phenomena and stated that the discharge
varied somewhat with the intensity of the rays, which was tested
in each instance by the relative luminosity of the fluorescent
screen, and by the relative darkness produced upon the photo-
graphic plate in several instances. Electrified bodies, whether
conductors or insulators, were discharged when placed in the
path of the rays. All bodies whatsoever behaved in the same
manner when charged. They were all discharged equally by
the X rays. He noticed that " If an electrical conductor is sur-
rounded by a solid insulator such as paraffin instead of by air,
the radiation acts as if the insulating envelope were swept by a
flame connected to earth." Upon surrounding said paraffin by
a conductor connected to earth, the radiation no longer acted on
the inner electrified conductor. The above observations led him
to believe that the action was indirect and had something to do
with the air through which the X-rays passed. In order to
prove this, it was necessary for him to show that air ought to be
able to discharge the bodies if first subjected to the rays, and
then passed over the bodies. The apparatus for performing an
experiment to test this prediction is shown in Fig. L, which
serves to illustrate also the manner in
which he prevented electrostatic influ-
ences of the discharge tube, leading in
wires and induction coil. 71, near cen-
tre. For this purpose he built a large
room in which the walls were of zinc cov-
ered with lead. The door for his entrance
9~~ [L ? ; and exit was arranged to be closed in an
air-tight manner. In the side wall oppo-
site the door there was a slit 4 cm. wide,
covered hermetically with a thin sheet of
aluminum for the entrance of X-rays from
the vacuum tube outside of the room. All the electrical ap-
paratus connected with the generation of the X-rays was outside
of the room. No force whatever came into the room, therefore,
except the X-rays through the aluminum. 71. In order to
show that air which had been subjected to the X-rays would
FIG. L.
77
discharge a body immediately afterwards upon coming in con-
tact therewith, he arranged matters so that the air was propelled
by an aspirator. He passed air along a tube made of thick
metal so that the rays could enter only through a small alu-
minum window near the open end. At over a distance of 20
cm. from the window was an insulated ball charged with elec-
tricity, and connected to any electroscope or electrometer. The
professor used a Hankel electroscope. No published sketch was
made by Roentgen ; therefore, that shown in the figure was
produced by inference from the description. The operation. was
as follows : The X-rays passed into the room through the alu-
minum window, and then into the metal tube through its alu-
minum window. When the air was at rest, the ball was not
discharged. When the aspirator was at work, however, so that
the air moved past the aluminum window and past the ball, the
latter was discharged whether electrified positively or nega-
tively. He modified the operation by maintaining the ball at a
constant potential by means of accumulators, while the air which
had been treated by X-rays was passed by the ball. " An elec-
tric current was started as if the ball had been connected with
the wall of the tube by a bad conductor." He was not sure
whether the air would retain its power to discharge bodies as
long as it remained out of contact with any bodies. He deter-
mined, however, that any slight " disturbance " of the air by a
body having a large surface and not electrified, rendered the air
inoperative. He illustrated this by saying that " If one pushes,
for example, a sufficiently thick plug of cotton-wool so far into
the tube that the air which has been traversed by the rays must
stream through the cotton-wool before it reaches the ball, the
charge of the ball remains unchanged when suction is com-
menced." With the cotton- wool immediately in front of the win-
dow, it had no effect, showing, therefore, that dust particles in
the air are not the cause of the communication of the force of
the discharge from the X-rays to the electrified body. Very fine
wire gauze in several thicknesses also prevented the air from
discharging the body when placed between the aluminum win-
dow and the ball within the thick metal tube, as in the case of
the cotton plug. Similar experiments were instituted with dry
hydrogen instead of air, and, as far as he could discern, the bod-
ies were equally well discharged, except possibly a little slower
in hydrogen. He experienced difficulty in obtaining equally
powerful X-rays at different times. All experimenters are ac-
quainted with this difficulty. Further, he called attention also
to the thin layer of ak which clings to the surface of the bodies,'
78
and which, therefore, plays an appreciable part in connection
with the discharge. 16, near end. In order to test the matter
further as to discharge of electrified bodies, he placed the same
in a highly exhausted bulb and found that the discharge was in
one case, for example, only -fa as rapid as in air and hydrogen
at ordinary pressure, thereby serving as another proof that gas
was the intermediate agency. Allowance should be made in all
experiments in connection with the discharging quality of X-
rays. The surrounding gas should be taken into account.
900. APPLICATION OF PRINCIPLE OF DISCHARGE BY X-RAYS.
Professor Robb, of Trinity College, (Science, Apr. 10, '96), pro-
posed and explained and practically tested the principle of the
discharge of X-rays to determine the relative transparencies of
substances to X-rays. He plotted a curve in which the co-or-
dinate represented the charge of the condenser in micro-coul-
ombs, and the abscissae the time between charging and dis-
charging the condenser. The same plan could be adopted, he
suggested, for making quantitative measurements of the inten-
sity of X-rays from different tubes or the same discharge tube
at different times. J. J. Borgmann, of St. Petersburg, probabl7
was the first to show that X-rays charged as well as discharged
bodies. See The Elect., Lon., Feb. 14, '96, p. 501. Soon, a simi-
lar announcement was made by Prof. Righi, of Bologna. 90.
90^4. BORGMANN AND GERCHUN'S EXPERIMENTS. ACTION OF
THE X-RAYS ON ELECTROSTATIC CHARGES AND (LA DISTANCE EX-
PLOSIVE.) Comptes Rendus, Feb. 17, '96 ; from Trans., by Louis
M. Pignolet. A positively charged zinc disk connected to an
electroscope lost its charge almost instantly and acquired a
negative charge. When the charge on the zinc disk was nega-
tive, the loss was much slower and was not complete, a certain
charge remaining. When the rays fell upon two small platinum
balls connected to the terminals of an induction coil but separ-
ated beyond its sparking distance, sparking took place between
them, showing that X-rays, like ultra-violet rays, increase the
sparking distance of static charges.
90^. RIGHI'S EXPERIMENTS. BODIES IN THE NEUTRAL OR
NEGATIVE STATE, POSITIVELY ELECTRIFIED BY X-RAYS. Comptes
Rendus, Feb. 17, 1896. From Trans, by Louis M. Piguolet. The
measurements were made by this eminent Italian physicist, with
a Mascart electrometer connected with the bodies upon which
the X-rays impinged and enclosed in a grounded metallic case
(Faraday cylinder) provided with an aluminum window for the
entrance of the rays. A metallic disk connected with the elec-
trometer lost its charge rapidly whether positive or negative.
79
99-5*. Initial positive charges were not completely dissipated;
negative charges were not only completely dissipated but the
bodies acquired positive charges. Disks in the neutral state were
charged positively by the X-rays the same as takes place with
ultra-violet rays. The final positive potential was greater for
copper than for zinc and still greater for retort carbon (" le car-
bon de cornue" 90*:. at end. The various results are not conflicting
if the particular materials are taken into accounts, goc at end.
goc. The experiments of Prof. Minchin, an expert in such
measurements, are properly described here, in that they seem to
clear up the superficial ambiguity. He formulated the conclu-
sion (The Elect., Lon., Mar. 27, 96, p. 736) thus: "The X-rays
charge some bodies positively and some negatively, and what-
ever charge a body may receive by other means, the X-rays
change it, both in magnitude and sign, to the charge which they
independently give to the body." Thus, in the case of mag-
nesium, if the same is first positively charged by any suitable
means, then will the X-rays not only discharge it, but electrify
it negatively, while if this metal is first negatively charged, the
X-rays either diminish or increase the discharge. It must be
remembered, however, that this is not true with all metals, for
he found that gold, silver, copper, platinum, iron, aluminum,
bismuth, steel and antimony, are all positively electrified.
90^. BENOIST & HERMUZESCU'S EXPERIMENT. NEGATIVE
CHARGES DISSIPATED FASTER THAN POSITIVE BY X-RAYS. RATE
DEPENDS UPON ABSORPTION. LAW FORMULATED. Comptes Rendus,
Feb. 3, Mar. 17 and April 27, '96. They observed that the rays
dissipated entirely the charge of electrified bodies in their path,
and that negative charges were dissipated more rapidly than
positive. 99(7. They also noticed the discharge augments
with the opaqueness of the body and that the effect is more
considerable wit?i two thin superposed sheets than with one. In
experimenting upon the influence of the discharge of the gas-
eous dielectric in which the bodies were located, they formulated
the following law. The rapidity of the dissipation of the electric
charge of an electrified body under the same condition varies as
the square root of the density of the gas surrounding the body.
The dissipation of the electric charge depends upon the na-
ture of the electrified body, due to a sort of absorbing power
( ggM) connected with the opaqueness of the body and upon
the nature of the surrounding gas, due to the density of the gas
or when passing from one gas to another. (From trans, by
Louis M. Pignolet.)
91. Before Roentgen published in his second paper of Mar.
8o
9, '96, an account of his focus tube, the Kings College published
a description of an exactly similar one, represented in the cut.
TYPICAL Focus TUBE.
See Elec. Rev., Lon., Mar. 13. '96, p. 340. The cathode is con-
cave and the anode is formed of platinum and is plane and at
such an angle that the X-rays generated, 636, on diffusion of
internal cathode rays, will be thrown out through the thin walls
of the bulb. 55 and 57. As the rays eminate from a point, the
shadows are much clearer, especially in conjunction with power-
ful rays permitting several feet between the object and the tube.
Mr. Shallenberger was among the first, and was the first as far
as the author knows (Elect. World, Mar. 7, '96,866 cut reproduced)
to originate the use of an X-ray focus tube.
910. APPARATUS EMPLOYED. Prof. Roentgen paid tribute to
Tesla, by alluding to the advantages resulting from the use of
the Tesla condenser and transformer. In the first place, he
noticed that the discharge apparatus became less hot, and that
there was less probability of its being pierced. Again the va-
cuum lasted longer, at least in the case of his particular appa-
ratus. Above all, stronger X-rays were produced. Again careful
adjustment of the vacuum was not as necessary as with the
Ruhmkorff coil.
92. X-RAYS AND LONGITUDINAL VIBRATIONS. Prof. Roentgen
did not consider X-rays and ultra-violet rays to be of the same
nature, although they produced many common effects. The
X-rays, as he found, by the above related experiments, behaved
quite differently from the ultra-violet rays, which are highly
refrangible, practically all subject to reflection, capable of being
polarized, and absorbed according to the density of the absorb-
ents. For valid reasons, the X-rays cannot be infra-red rays.
While he does not affirm any theory, yet he suggests the theory
of longitudinal waves for explaining the properties of X-rays.
8i
(This was not suggested again in his second anouncement.) He
stated that the hypothesis needs a more solid foundation before
acceptance. The reason why Roentgen termed the energy X-
rays is simply because X in algebra represents an unknown
quantity.
93. At the Johns Hopkins University, U. S., in 1884, Sir
William Thomson, (Kelvin) delivered a lecture in which he
argued that the production of longitudinal vibrations,by electrical
means, is reasonable and possible of occurrence. J. T. Bottomly,
in Nature, Lon. Feb., (see also Elect. Eng., N. Y., Feb. 19, '96, p.
187) called attention to this lecture as being of interest in view
SHALLENBERGER APPARATUS AND Focus TUBE. 91.
of Roentgen's suggestion about longitudinal vibrations. Lord
Kelvin called attention to what had been developed in connec-
tion with the electromagnetic theory of light and referred to his
own work in 185 4, in connection with the propagation of electric
impulses along an insulated wire surrounded by gutta percha,
but he said that at that time no one knew the relation between
electro-static and electro-magnetic units. The part of the lecture
referring particularly to the possibility of longitudinal waves in
luminiferous ether by electrical means reads as follows. " Sup-
pose that we have at any place in air, or in luminiferous ether
(I cannot now distinguish between the two ideas) a body that,
through some action we need not describe, but which is con-
82
ceivable, is alternately, positively and negatively electrified ;
may it not be that this will give rise to condensational waves ?
Suppose, for example, that we have two spherical conductors
united by a fine wire, and that an alternating E. M. F. is produced
in that fine wire, for instance, by an alternate current dynamo-
electric machine, and suppose that sort of thing goes on away
from all other disturbance at a great distance up in the air,
for example. The result of the action of the dynamo-electric
machine will be that one conductor will be alternately, positively
and negatively electrified, and the other conductor negatively
and positively electrified. It is perfectly certain, if we turn the
machine slowly, that in the air in the neighborhood of the con-
ductors, we shall have alternately, positively and negatively
directed electric force with reversals of, for example, two or
three hundred per second of time, with a gradual transition
from negative, through zero to positive, and so on ; and the
same thing all through space ; and we can tell exactly what the
potential and what the electric force are at each instant at any
point. Now, does any one believe that, if that revolution were
made fast enough, the electro-static law of force, pure and
simple, would apply to the air at different distances from each
globe ? Every one believes that if the process can be conducted
fast enough, several million times, or millions of millions times
per second,we should have large deviations from the electrostatic
law in the distribution of electric force through the air in the
neighborhood. It seems absolutely certain that such an action
as that going on would give rise to electrical waves. Now, it
does seem to me probable that these electrical waves are con-
densational waves in luminiferous ether; and probably it would
be that the propagation of these waves would be enormously
faster than the propagation of ordinary light waves. " Notice
that the above was written twelve years prior to Roentgen's-
discovery.
94. Prof. Schuster, in Nature, Lon., Jan- '96, stated that the
great argument against the supposition of waves of very small
length lies in the absence of refraction, but questioned whether
this objection is conclusive. He further stated: " The properties
of the ether may remain unaltered within the greater part of
the sphere of action of a molecule. The number of molecules
lying within a wave length of ordinary light is not greater than
the number of motes which lie within a sound wave, but, as far
as I know, the velocity of sound is not materially affected by
the presence of dust in the air. Hence there seems nothing-
impossible in the supposition that light waves, smaller than.
83
those we know of, may traverse solids with the same velocity as
a vacuum. We know that absorption bands greatly affect the
refractive index in neighboring regions ; and as probably the
whole question of refraction resolves itself into one of resonance
effects, the rate of propagation of waves of very small lengths
does not seem to me to be prejudged by our present knowledge.
If Roentgen rays contain waves of very small length, the vibra-
tions in the molecule which respond to them, would seem to be
of a different order of magnitude from those so far known. Pos-
sibly, we have here the vibration of the electron with the mole-
cule, instead of the molecule carrying with it that of the electron.""
95. Prof. J. J. Thomson showed how it was possible that
" longitudinal waves can exist in a medium containing moving
charged ions, and in any medium, provided the wave length is
so small as to be compared with molecular dimensions, and pro-
vided the ether in the medium is in motion. It follows from the
equation of the electro-magnetic field that the ether is set in
motion in a varying electric field. These short waves would not
be refracted, but in this respect they do not differ from trans-
verse waves, which on the electro-magnetic theory would not
be refracted if the wave length were comparable with molecular
distances." From Elect. Eng., N. Y. Mar., 18, '96, p. 286, in
reference to a paper before the Cam. Phil. So.
96. One of the very first questions asked in reference to a
discovery is as to its practical utility. Already, we have import-
ant applications in one of the most humane directions, and that
is in connection with diagnosis. Sciagraphs can also be employed
in schools for the purpose of education, in some departments of
anatomy, etc. The interest that it excites and the amusement
that it affords are not to be overlooked, for anything in the
nature of recreation possesses utility. However, we may greatly
thank all experimenters who have investigated the subject, and
who have not left its development alone to Roentgen ; for pre-
dictions as to the utility of a discovery, however, apparently
exaggerated, are very often proved, by subsequent develop-
ments, to have been underrated. Upon this point Prof. Boltz-
mann, in Zeit. Elect., Jan. 15, '96, see also, The Elec., Lon., Jan.
31. '96, p. 447, stated, " If we remember to what discoveries the
most insignificant new natural phenomenon, such as the attrac-
tion of small objects by rubbed amber, of iron by the lode-stone,
the convulsive twitches of a frog's leg due to electric discharges,
the influence of the electric current upon the magnetic needle,
electro-magnetic induction etc., has led us, one can imagine to-
8 4
what applications an agent will be turned, which a few weeks
after its discovery has given rise to such surprising results."
97. Soon after hearing, (about the first of Feb. '96,) of the
Roentgen discovery, it occurred to the author to carry on ex-
periments with fluorescence, but finding that it was inconvenient
to work in a perfectly dark room, and, recognizing that black
card-board had practically no effect upon absorbing the X-rays,
he devised a sciascope (daily papers, Feb. 13, and Elect. Eng., Feb.
19) which he afterwards learned was independently invented
and used at about the same time by Prof. William F. Magie, of
Princeton University, (see Amer. Jour. Med. Sci., Feb. 7, '96 and
Feb. 15, '96) and by Prof, E. Salvioni, of Italy under the name
of cryptoscope, (see Med. Sur.Acad. of Perugia, Italy, Feb. 8, '96.)
In about a month afterwards (Elect. Eng., N. Y., Apr. i, '96, p.
340) the instrument (with phosphorescent calcic tungstate 132
in place of fluorescent barium platino cyanide) was again pub-
lished under the name of the Edison fluoroscope. There are
probably many other claimants some professor in London
name forgotten. They all consist of a tapering tube with a
sight hole at one end and a fluorescent screen in the other, which
is closed by opaque card board. (Frontispiece at Chap. X). For
the sake of conformity, the words sciagraph and sciagraphy and
similar derivatives, and in view of the meaning of the radical
definitions, have been employed throughout the book. The ob-
jection to the word fluoroscope is that the instrument is prac-
tically universally employed in seeing the shadows of objects,
otherwise invisible to the naked eye, rather than to test fluores-
cence. The name sciascope was early suggested by Prof. Magie.
For those who wish to make a screen, the author may state that
he obtained a good one by mixing pulverized barium platino
cyanide with varnish and spreading the mixture over a sheet of
tracing cloth.
CHAPTER VIII.
970. HERTZ' EXPERIMENTS.
BY ULTRA-VIOLET LIGHT OF
OF LIGHT. Berlin Akad. II
p. 983. English translation of the
ELECTRIFIED BODIES DISCHARGED
A SPARK AND BY OTHER SOURCES
p. 487, '87. Wied Ann. XXXI,
Macmillan, p. 63, '93.
above. Lon. and N. Y.
From notes by Mr. N. D. C. Hodges.
This is the all-important initial work of H. Hertz. The source
of light was a spark, and the great discovery resulted from a
combination of circumstances and was unsought ; but by study-
ing and testing the matter, he found the cause. Two induction
coils, a and , having interrupter d, were included in the same cir-
* cuit, as shown in the figure. The sparking of the active one (A)
increased the length of the spark of the passive (B) 10. He
sought the cause. The discharge was more marked as the dis-
tance between the sparks was reduced. Sparks between the
knobs had the same effect as those between points ; but the
effect was best displayed when the spark B was between knobs.
The relation between the two sparks was reciprocal. The dis-
charging effect of the active spark (A) spread out on all sides,
according to the laws of light,
first suggesting that light
was the cause. Most solid
bodies acted as screens, s.
Liquid and gases served
more or less as screens. The
intensity of the action in-
creased by the rarefaction of
the air around the passive
spark, /. e. y in a discharge
tube. The radiations from
the spark, A, reflected from
most surfaces, according to the laws of light, and refracted ac-
cording to the same laws, caused the discharge. The ultra-
violet light of the spark A was inferred to be the active agent in
producing the discharge. The same effect was produced by
other sources of light than the electric spark. The conclusions
85
86
were afterwards confirmed by many, and sub-ordinate discov-
eries originated. 98-99 T.
97^. WlEDEMANN AND EBERT's EXPERIMENT. LlGHT DlS-
CHARGES CATHODE, BUT HAS No INFLUENCE UPON ANODE, NOR
AIR-GAP. DIFFERENT GASES AND DIFFERENT PRESSURES. Wied.
Ann. XXXIII, p. 241. 1888. From notes by N. D. C.
Hodges. The arc-light was used in place of the active spark of
Hertz. Principal result was that the effect depended on the
illumination of the cathode ( 99.) The illumination of the
anode or of the spark-gap did not influence the discharge. The
very character of the charge was altered by the action of light
upon the cathode. The influence of the illumination of the
cathode did not consist solely at the starting of the spark, but
lasted as long as the sparks continued to pass. With decreasing
pressure of surrounding gas, the effect first increased ( 970) to
a maximum, and then decreased ( 54). The illumination had
an effect on the path of the sparks, the path being perpendicu-
lar to the rays of light. The best results were obtained with
carbonic acid gas. Hydrogen was next, and then air. They
were contained in the tubes surrounding the poles. The char-
acter of the gas also had an influence on the rays which would
produce the effect, with carbonic acid gas the effect showing
itself even with the visible rays.
98. ELSTER AND GEITEL'S EXPERIMENT. NEGATIVELY CHARGED
BODIES DISCHARGED BY LIGHT. Wien. Berichte. Vol. CI, p. 703,
'92. Wied. Ann. Vols. XXXVIII, XXXIX, XLI, XLII, XLIII,
XLIV, XLVI, XLIII, LII. Nature, Lon., Sept. 6, '94, p.
451. The elements employed for carrying on the experiment
consisted of a delicate electroscope and certain metals, includ-
ing aluminum, amalgamated zinc, magnesium, rubidium, potas-
sium and sodium. Some of the experiments were made on the
top of Mount Sonnblick, the same being 3,100 m. high, where the
discharging power of light was found to be about twice as great
as at Wolfenbuttel, which was at the level of 80 m. The whole
time for the discharge was only a matter of a few seconds. The
greater rapidity of discharge at the higher level was attri-
buted to the greater proportion of ultra-violet rays (Hertz),
which are the most easily absorbed by the atmosphere, accord-
ing to Langley. All metals are not discharged alike by the
action of light. The law follows the electro-positive series in
such a way that the more electro-positive the metal, the longer
the wave length of light necessary to produce the discharge.
In experiments with potassium, sodium and rubidium, they
made them successively, the cathode in a bulb of rarefied hy-
87
drogen. In this case it was found that the light of a candle,
even at so great a distance as 7 m, would cause the discharge.
Rubidium was sensitive in this respect to the red light from a
lieated rod of glass. Elster and Geitel were able also to dis-
charge, by light, some non-metallic bodies, like calcic sulphide,
when so prepared that it had the property of phosphorescing,
and also darkly colored fluorites. Independently, the phenom-
enon is of importance, because Elster and Geitel determined
that there was some common cause as to the discharge of bodies
of light and the discharge from the earth's surface. A series of
experiments lasting three years, consisted in investigating the
relation of the ultra-violet rays from the sun simultaneously to
the quantity of charge in the atmosphere. The results acted as
evidence of the explanation of the daily and annual variation
of atmospheric potentials. These experiments are of import-
ance in connection with X-rays, because Rontgen and Prof. J.
J. Thomson subsequently, and possibly others independently,
discovered that X rays produce, not only a like, but a more
extended action in that there is not so great a difference be-
tween their power to discharge negatively and positively elec-
trified bodies. 900. In the further developments of their
ideas, they tried the action of diffused day-light upon a Geissler
tube traversed by vibrations which were produced by a Hertz
vibrator (see recent book on Hertzian waves), the tube having
an electrode of metal of the alkaline group. They were able
to adjust the combination so that the presence of a little day-
light would initiate a luminous discharge, while in the dark such
a charge ceased. 14 a.
99. ELSTER AND GEITEL'S EXPERIMENT. EFFECT OF POLAR-
IZED LIGHT UPON THE CATHODE. Berlin Akad. '95. Nature,
Lon., March 28, '95, p. 514. Proc. Brit. Asso., Aug. 16, '94;
Aug. 2 3> *94> P- 46. The X-rays have properties similar to
those of light, and have their source in electricity. Quincke
discovered that light which has been polarized perpendicularly
to the plane of incidence is greatly increased as to its power of
penetrating metals. Elster and Geitel used the following ap-
paratus to determine the relation between polarized light and
electricity. The current varied according to the angle of inci-
dence and the plane of polarization. The apparatus comprised
the following elements : An exhausted bulb, provided with a
platinum anode, and a cathode consisting of potassium and so-
dium, combined in the form of a liquid alloy having a bright
surface of reflection. The source of light was an oxyhydrogen
flame, which played upon zircon instead of lime ; a lens
88
changed the diverging rays to parallel rays, which were polar-
ized by a Nichol prism and allowed to fall upon the cathode.
The electrodes of the vacuum bulb were connected to the poles
of a generator of a current of about 400 volts. " The strength,
of the current was greatest when the plane of polarization was
perpendicular to the plane of incidence /. <?., when the electric
displacements constituting light, took place in the plane of in-
cidence, and when the angle of incidence was about 60, i. e. y
the polarizing angle of the alloy itself." Prof. Sylvanus P.
Thompson confirmed these results by experiment. The rate of
discharge was greatest, he said, when the plane of polarization
was such that the Fresnellian vibration " chopped into " the sur-
face. Polarized light, he reminded them, produced similar
results upon selenium.
Although the domain of this book is necessarily limited to the
consideration of phenomena connected with the internal and
external energy of a discharge tube, yet if any other one sub-
ject is of special interest and utility in connection with the con-
sideration of X-rays, it is that concerning the relation between
the electric discharge and light, which has been thoroughly
studied only during the past few years, and the accounts of the
researches recorded in various periodicals and academy papers.
Those readers, however, who desire to study this exceedingly
interesting and novel branch of science, which in connection
with the action of the internal cathode rays and X-rays upon
electrified bodies, tends to uphold Maxwell's theory as developed
by mathematics and based upon early known facts and predicted
discoveries, may find volumes upon this subject by referring to
the citations below, named by Mr. N. D. C. Hodges and obtained
by him by a search in the archives of the Astor Library. Of
especial interest are those of Branley, 997, 99./, 99<2, 99-S, 99^.
Some notion as to the contents of the citations are given here
and there.
ggA. KOCH'S EXPERIMENT. THE Loss OF ELECTRICITY FROM A
GLOWING ELECTRIFIED BODY. Wied. Ann., XXXIII., p. 454, '88.
99.Z?. SCHUSTER AND ANPENIUS' EXPERIMENT. THE INFLUENCE
OF LIGHT ON ELECTROSTATICALLY CHARGED BODIES. Proc. R.
So., Lon., LXII., p. 371, '87 ; Proc. Swedish Acad., LXIV., p. 405,
'87. Many recent periodicals have set forth that ultra-violet
light will discharge only negatively charged bodies. While this
is practically or sometimes the case, yet these experimenters
found that a positive charge was dissipated very slowly. They
confirmed the results that the ultra-violet rays played the prin-
8 9
ciple part in the removal of a negative charge . Polishing the
surface accelerated the action. 99, near beginning.
99(7. RIGHI'S EXPERIMENT. SOME NEW ELECTRIC PHENOMENA
PRODUCED BY LIGHT. Note 2-4, Rend. R. Acad. die Lincei, May
6, 20, and June 3, '88.
99-A RIGHI'S EXPERIMENT. SOME NEW ELECTRIC PHENOMENA
PRODUCED BY ILLUMINATION. Rend. R. Acad. die Lincei. VI.,
p. 135, 187, '88. Confirmation of the results of other physicists,
and a quantitative measurement determining that the E. M. F.
between copper and selenium was increased 25 per cent, by illu-
mination by an arc light. The selenium was in the form of
crystals mounted upon a metal plate.
99.fi 1 . STOLSTOW'S EXPERIMENT. ACTING-CURRENT THROUGH
AIR. C. R., CVL, pp. 1593 to 95, '88. Liquids tested. Greatest
absorbents of active rays most quickly discharged.
99^. RIGHI AND STOLSTOW'S EXPERIMENTS. KIND OF ELEC-
TRIC CURRENT PRODUCED BY ULTRA-VIOLET RAYS. C. R.,
CVI,pp. 1149 to 52, '88. The discharge was accelerated by
using a chemically clean surface. The burning of metals, for
example, aluminum, zinc or lead in the arc light increased the
discharging power.
99(9. BICHAT & BLONDOT'S EXPERIMENT. ACTION OF ULTRA-
VIOLET RAYS ON THE PASSAGE OF ELECTRICITY OF Low TEN-
SION THROUGH AIR, Comptes Rendus. CVI, pp. 1,349 to 51.
88. They employed arc lamps whose carbons had aluminum
cores.
99/7". NACARRI'S EXPERIMENT. THE DISSIPATION OF ELEC-
TRICITY THROUGH THE ACTION OF PHOSPHOROUS AND THE ELEC-
TRIC SPARK. Attidi Torino. XXV, pp. 252 to 257. '90. The
loss of charge was eighteen times less rapid in the dark through
the air in a bottle, than when a piece of luminous phosphorous
was placed in the bottle. The introduction of turpentine,
which checked the glowing of the phosphorous, retarded the
loss of charge.
99/. BRANLY'S EXPERIMENT. PHOTO-ELECTRIC CURRENT BE-
TWEEN THE TWO PLATES OF A CONDENSER. C. R. CX, pp. 898
to 901. '91. A positive charge was dissipated, and by a pe-
culiar arrangement of the plates, screens, etc., and with partic-
ular materials, he was able to show that the rates of loss of a
positive and negative charge were about equal. Numerous
tests were instituted. If he is not mistaken, how closely re-
lated are X-rays and light. 90. Those who wish to more
thoroughly investigate this matter and verify the same, should
study these experiments more in detail in connection with
I
FROM SCIAGRAPH OF FROG, THROUGH SMALL HOLE IN DIAPHRAGM,
AS IN FIG. i, p. loo.
9 1
Schuster's and Anpenius' experiments ( 99^?), whose arrange-
ment of the plates was the same as those of Branly.
99/. BRANLY'S EXPERIMENT. Loss OF BOTH ELECTRICITIES BY
ILLUMINATION WITH RAYS OF GREAT REFRANGIBILITY. C. R.
CX, pp. 751 to 754. '90.
99^". RIGHI'S EXPERIMENT. ELECTRIC PHENOMENA PRO-
DUCED BY ILLUMINATION. Luer's Rep. XXV, pp. 380 to
382. '89.
99Z. BORGMANN. ACTINO-ELECTRIC PHENOMENA. C. R. CVIII,
P- 733- >8 9- Jour.d. Russ. Phys. Chan. Ges. (2) XXI, pp. 23 to
26 '89. The photo-electric effect not instantaneous. A tele-
phone served in the place of the galvanometer to detect the
discharge.
99^/. STOLSTOW'S EXPERIMENT. ACTINO-ELECTRIC INVESTI-
GATIONS. Jur. d. Russ. Phys. Chan. Ges. (7-8) XXI, pp. 159 to
207. It is necessary that the rays of light should be absorbed
by the charged surface before having the discharging influence.
998. All metals are subject to the action, and also the aniline
dyes. Two plates between which there is a contact difference
of potential generate a current so long as the negative plate is
illuminated. The effect is increased with the increase of tem-
perature and is only found in gases, and is therefore of the
nature of convection. He determined these principles by con-
tinuous work for two years. It should be remembered that in
all these researches, the arc light is preferable, because the ultra-
violet spectrum is six times as long as that given by the sun.
997V. MEBIUS' EXPERIMENT. AN ELECTRIC SPARK AND A
SMALL FLAME EMPLOYED. Bihang till K. Svenska Vet.-Akad.
Hand. 15, Afd. i, No. 4, p. 30, '89.
99(9. WORTHINGTON'S EXPERIMENT. DISCHARGE OF ELECTRI-
FICATION BY FLAMES. Brit. Asso. Rep., '90, p. 225.
gyP. FLEMING'S EXPERIMENT. DISCHARGE BETWEEN ELEC-
TRODES AT DIFFERENT TEMPERATURES IN AIR AND IN HIGH
VACUA. 99^/, near end. Proc. Ro. So., LXVII., p. 118.
99<2- BRANLY'S EXPERIMENT. HALLWACH AND STOLSTOW'S
EXPERIMENT. Loss OF ELECTRIC CHARGE. Lum. Elect., LXI. t
pp. 143 to 144, '91. Branly obtained quantitative results.
Hallwach found with the use of the arc light, a very small loss
of positive electricity at high potentials ; S^.c'istow, no such loss
at potentials under 200 volts. Branly, with a 50 element battery
and an arc light as the source of illumination, caused a discharge
and thereby a constant deflection of 1 24 degrees of the galvan-
ometer needle. The action of the light upon a positive disk
caused a deflection of only three degrees by the same battery.
9 2
With aluminum in the electrodes, the deflections were about
1400 and 24 respectively. Is it not sufficiently fully established
that ultra-violet light will discharge not only negative but posi-
tive electricity? He experimented with substances heated to
glowing or incandescence. Glass lamp chimneys at a dull, red
heat, when covered with aluminum, oxide of bismuth, or lead
oxides, withdraw positive charges. In the same way, for exam-
ple, behaves a nickel tube in place of the lamp chimney.
99^?. WANKA'S EXPERIMENT. A NEW DISCHARGE EXPERIMENT.
Abk. d. Deuts. Math. Ges. in Rrag., '92, pp. 57 to 63. He confirms
the principle that the ultra-violet rays are the most powerful.
A glass plate, which, as well known, cuts off most of the ultra-
violet rays, was properly interposed and then removed and the
difference noted.
996". BRANLY'S EXPERIMENT. DISCHARGE OF BOTH POSITIVE
AND NEGATIVE ELECTRICITY BY ULTRA-VIOLET RAYS. C. R. y
CXIV., pp. 68 to 70, '92. He further proves that ultra-violet
rays of light will dissipate a positive charge. The experiments
in this connection seem to prove more and more that the dis-
charging power is only a matter of sufficiently high refrangi-
bility of the rays of light.
997*. BRANLY'S EXPERIMENT. Loss OF ELECTRIC CHARGE IN
DIFFUSE LIGHT AND IN THE DARK. C, ./?., CXVI., pp. 741 to
744. '93. A polished aluminum sheet was attached to the ter-
minal of an electroscope properly surrounded by a metal screen.
After a few days, the plate acted like any other metal plate pol-
ished or unpolished ; it lost its charge very slowly, positive or
negative alike, independently of the illumination. If it is then
again polished, as for example, with emery paper and turpen-
tine, it loses its charge rapidly in diffused light, which has passed
through a pane of window glass, for example. Therefore, the
ultra-violet rays are not alone effective, although most effective.
The longer the time elapsing, after polishing, the slower the
discharge takes place. Zinc behaved likewise, only more slowly.
Other metals were tried. Bismuth acted differently from most
metals. Whether charged positively or negatively, they ex-
hibited rapid loss in the dark, in dry air under a metal bell, in-
dependently of the state of the polish.
CHAPTER IX.
100. THOMSON'S EXPERIMENTS. Elect. Eng., N. Y., Mar. n,
Apr. 8 and Apr. 22, '96. Elect. Rev., N. Y., Apr. 8, '96., p. 183.
STEREOSCOPIC SCIAGRAPHS. Elect. World, N. Y., Mar. 14, '96.
Prof. Elihu Thomson, of the Thomson-Houston Electric Com-
pany, described experiments to determine the practicability of
making stereoscopic pictures by X-rays. A solid object may
be considered as composed of points which are at different dis-
tances from the eye. By monocular vision, the solidity of an
object is not assured. However, by the use of both eyes, the
objects appear less flat. The experimenter used, as the differ-
ent objects, a mouse, also metal wires twisted together, and,
again, a block of wood having projecting nails. In order to
produce a stereoscopic picture with X-rays, he took a sciagraph
in the ordinary way. He then caused the relative displacement
of the discharge-tube and the object, and took another sciagraph.
By mounting the two sciagraphs in a stereoscope, he found that
the effect was as expected, and in the case especially of the
skeleton of the mouse, it was very curious, less like a shadow
picture and more like the real object. The picture was more
realistic, as in the well known stereoscope for viewing photo-
graphs.
101. THOMSON'S EXPERIMENT. MANIFOLDING BY X-RAYS. If
one desires to take a print of a negative, for example by means
of sun-light, it is evident that, on account of the opacity of the
photographic paper, only one sheet would be placed under the
negative for receiving a print. However, the X-rays are so
penetrating in their power that it is possible for them to pro-
duce sciagraphs through several sheets, and thereby to result in
the production of several pictures of the same object with one
exposure. Without an experiment to prove this, one might
argue that the chemical action of one sheet would absorb all
the energy. The experiment of Prof. Thomson shows that this
is not so. The elements were arranged as follows : First a
discharge tube ; then an object, namely, a key escutcheon of
iron ; then yellow paper ; then paste board ; then black paper ;
93
MULTIPLE SCIAGRAPHS. FIG. i, 101, p. 95
MULTIPLE SCIAGRAPHS. FIG. 2, 101, p. 95.
95
then two layers of albumen or sensitized paper ; then two
celirite printing papers ; then two platinum printing papers ;
then one celerete ; then six layers of sensitive bromide paper ;
then four layers of heavy sensitive bromide paper (heavier) ;
then three layers of black paper, and finally, at the maximum
distance from the discharge-tube, a sensitive glass plate of dry
gelatine, with its face up, thereby making twenty-five layers in
the aggregate. It is interesting to notice that an induction coil
was not employed, but a small Wimshurst machine, having con-
nected to each pole a small Leyden jar. 106. 1,200 dis-
charges occurred during exposure. The results were as follows :
No sciagraphs developed upon the albumen, celerite nor
platinum, which, it should be noticed, were merely printing
papers. 128. The impressions on the ten bromide papers
were weak. See Multiple Sciagrahs, Fig. 2, p. 94. He at-
tributed the reason of this to the thinness of the film. Al-
though the glass plate was furthest away from the discharge
tube, yet the impression was greater than on any of the papers,
the result being shown in Multiple Sciagraphs, Fig. i, p. 94.
He suggested that the plates for use with X-rays should have
unusually thick films. Incidentally he found that the intensify-
ing process could be employed with profit to bring out the small
details distinctly. Dr. Lodge also recommended thick films.
See The Elect. , Lon., Apr. 24, '96., p. 865.
loia. LUMIERE'S EXPERIMENT. ENORMOUS TRANSPARENCY
OF SENSITIVE PHOTOGRAPHIC PAPER. Comptes Rendus, Feb. 17, '96.
Translated by Mr. Louis M. Pignolet. With a ten-minutes ex-
posure, objects were sciagraphed through 250 super-imposed
sheets of gelatino-bromide of silver paper, to observe the ab-
sorption of the X-rays by the sensitive films. The one hundred
and fiftieth sheet was found to have an impression.
102. PROPOSED DOUBLE CATHODE TUBE. See also Elect. Rev.,
N. Y., Apr. 15, p. 191. The nature of this will be apparent im-
mediately from the cut which is herewith presented and entitled
" Standard X-Ray Tube." With unindirectional currents the
concave electrodes in the opposite ends may each be a perman-
ent cathode, while the upper terminal connected to the angular
sheet of platinum may be the anode. Cathode rays, therefore,
will be sent out from each concave disk, and striking upon the
platinum will be converted into X-rays, assuming that the pla-
tinum is the surface upon which the transformation from one
kind of ray to another takes place. 63, at end. This is called
a standard tube, because it may be employed with efficiency with
an) r kind of generator. #, 260, 115, 116 and 145. It is inter-
9 6
esting to notice a confirmation of the efficiency of such a tube,
for Mr. Swinton, in a communication to the Wurz Phys. Med. So.
(see The Elect., Lon., and Elect. Eng., N. Y., June 3,) showed and
described a picture of an exactly similar tube. By an experi.
ment, the tube operated as expected. First proposed by Prof.
Elihu Thomson, who is an author also of the following experi-
ment :
103. X-RAYS. OPALESCENCE AND DIFFUSION. Elect. World,
Apr. 25, '96. He alluded to opal glass and milk to illustrate
that light is reflected not only at the surface of a body, but from
STANDARD X-RAY TUBE.
points, or molecules, or particles, located underneath the surface.
By some experiments with X-rays, he found that they had a
similar property only not to such a large per cent., but on the
other hand by the way of contrast, there are many more sub-
stances opalescent to X-rays than there are to light, for the rea-
son that the former will penetrate more substances and to
greater distances. . He made many observations with a modified
sciascope, 105, by pointing it away from the discharge tube
and towards different substances struck by X-rays. To all ap-
pearances, such substances became the sources of the X-rays.
He alluded to Mr. Tesla's experiments on reflection, 146, but
97
noticed that there was a slight difference between reflection and
diffusion and he was satisfied that reflection took place from the
interior of the substances as well as from the surface. Metal
plates, he said, gave apparently little diffusive effect, appearing
to reflect feebly at angles equal to the incident angles. He al-
luded to Edison's experiment also, 133, with a large thick plate
cutting off the X-rays and attributed the luminosity of his modi-
fied sciascope to rays both reflected and diffused from surround-
ing objects, which generally as a matter of course, are more of
non-metallic objects than metallic, such as floor, ceiling, walls,
tables, chairs and so on. Evidently, the interior of one's hand
causes diffusion ; very little, however, for a sciagraph by means
of a focus tube gives wonderfully clear outlines, and yet the rays
do not come from a mathematical point. 88. Prof. Thomson
acknowledged that independently of himself, Dr. M. I. Pupin, of
Columbia College, had reported in Science, Apr. 10, '96, see also
Electricity, Apr. 15, '96, p. 208, upon investigations on the same
general subject, namely diffusion, and also referred to experi-
ments of Lenard, 69, and Roentgen on diffusion. Agrees also
with experiments of A. Imbert and H. Bertin-Sans in Comptes
Rendus, Mar. 2, '96. He suggested that this property of diffusion
acted as an explanation why sciagraphs can never have abso-
lutely clearly cut shadows of the bones or other objects imbedded
in a considerable depth of flesh.
1030. A. IMBERT AND H. BERTIN-SANS' DIFFUSION AND RE-
FLECTION IN RELATION TO POLISH. X-RAYS. Comptes Rendus,
Mar. 2, '96. Translated by Louis M. Pignolet. They concluded,
winder the conditions of their experiments, that if X-rays were
capable of reflection it was only in a very small proportion ; on
the other hand, the rays can be diffused en assez grande quan-
tite, the intensity of the diffusion appearing to depend much
more upon the nature of the diffusing body than upon its degree
of polish. From this they attributed to the rays a very small
wave length, such that it would be impossible to get in the de-
gree of polish necessary to obtain their regular deflection.
Perrin attempted unsuccessfully to reflect the rays from a pol-
ished steel mirror and a plate of " flint," but with exposures of
-one hour and seven hours respectively, nothing was obtained.
From trans, by L. M. Pignolet, Comptes Rendus, Jan., 96. By
exposing a metal plate to the rays and suitably inclining it in
front of the opening, Lafay also proved reflection, for it was
possible to discharge the electrified screen ; hence, as he called
it, diffused reflection. Comptes Rendus, Apr. 27, '96 ; from trans,
by L. M. Pignolet.
9 8
104. FLUOROMETER. He constructed an instrument for com-
paring the merits of different discharge tubes, and for indicat-
ing the comparative luminosity of different screens subjected
to the action of the same discharge tube. The instrument
served also to act as an indicator of the diffusing power of dif-
ferent materials. " By placing two exactly similar fluorescent
screens at opposite ends of a dark tube, and employing a Bunsen
photometer screen, movable as usual between the screens, a
comparison of the diffusing power of different materials might
be made by subjecting the pieces placed near the ends of the
photometer tube outside, to equal radiation from the .Crookes*
tube." From Prof. Thomson's description.
The author performed some experiments (Elect. Eng., N. Y.,.
Apr. 15, '96, p. 379) in relation to candle-power of X-rays by
looking into a sciascope and moving it away until the luminos-
ity just disappeared. He then detached the black paper cover
from the phosphorescent screen and pointed the sciascope to-
ward a candle flame and receded away until the fluorescence
also disappeared. The distances, with different candles, would,,
of course, somewhat vary, but it would in the rough be a con-
stant quantity, while different discharge tubes would cause the
vanishing fluorescence at different distances. Now, assuming
that the X-rays vary inversely as the square of the distance,
as believed by Rontgen, their power to fluoresce could, there-
fore, always be named as so much of a candle-power.
105. SIMPLE DEVICE FOR COMPARING AND LOCATING THE
SOURCE AND DIRECTION OF X-RAYS. PHOSPHORESCENCE NOT
ESSENTIAL. In the ordinary sciascope, the fluorescent screen
is located at one end, and the eyehole at the other. He modified
this construction by employing a long straight tube, made of
thick metal, so that X-rays could not enter through the wall.
About at the centre of the tube was a diaphragm of a fluor-
escent material. Now, it is evident that if this is directed to-
ward the phosphorescent spot and placed very close to the
same, and the other end be looked into, the screen will become
fluorescent, if X-rays are emitted from the area expected. Such
a result occurred. With this instrument, he was able to show, in a
similar way, that X-rays did not come from the anode, nor from
the cathode directly. In one case, he provided a piece of platinum
within the discharge tube, in such a position as to be struck by
the cathode rays. 91 and 116. The instrument showed that
X-rays radiated from the platinum, although the latter was not
luminous nor phosphorescent, illustrating again that phosphor-
escence is not a necessary accompaniment of X-rays, and assist-
99
ing in upholding the principle that as the phosphorescence
diminishes by increase of vacuum and increase of E. M. F., the
X-rays increase. It should be noticed that Prof. Thomson em-
phasizes that the tube should be made of thick metal.
106. RICE'S EXPERIMENT. APPARATUS FOR OBTAINING X-
RAYS. 109, 114, 131, 137. TUBE ENERGIZED BY A WIMSHURST
MACHINE. Elect. Eng., N. Y., Apr. 22, p. 410. Roentgen had
always employed the induction coil. As to those who first ex-
cited the discharge tube by the Holtz or Wimshurst machine or
generators of like nature, it is not certain ; but, according to
public records, they were independently Prof. M. I. Pupin, of
Columbia College, and Dr. William J. Morton, of New York.
See Electricity, N. Y., Feb. 19, '96. The accompanying cut
marked " Rice's Experiment, Fig. i," is a diagram representing
the several elements of the apparatus, while " Rice's Experi-
ment, Fig. 2," shows what kind of a sciagraph can be obtained
by means of a Wimshurst machine. 101, at centre. The de-
tails of the apparatus as employed by Mr. E. Wilbur Rice, Jr.,
Technical Director of the General Electric Co., were as follows :
A Wimshurst machine, having a glass plate 16 inches diameter,
coupled up with the usual small Leyden jars, spark under best
conditions of atmosphere, etc., 4 inches. " The usual method of
taking pictures with such a machine is to connect the interior
coatings of the two jars, respectively, to the positive and nega-
tive conductors of the machine, the terminals of the discharge
tube being connected between the external coatings of the
Leyden jars. In this condition, the disruptive discharge of the
Leyden jars passes through the tube and across the balls upon
the terminals of the conductors of the machine, the length cf
spark being regulated by separating the balls in the usual way.''
Later, he found that by omitting the Leyden jars, the genera-
tion of the X rays was practically non-intermittent. He there-
fore connected the terminals of the discharge tube directly to
those of the Wimshurst machine as indicated in " Rice's Ex-
periment, Fig. i," which also illustrates the details in the carry-
ing out of the experiment for obtaining the picture, Fig. 2, of
the purse containing the coins and a key. The principal feature
was the introduction of a lead diaphragm containing a small
central opening 7-8 inch diameter opposite the fluorescent spot.
Sciagraphs taken thus required a little more time, about 60 min-
utes, while without the diaphragm, the time could be shortened
to about 30 minutes, but the shadows were not so clear in the
latter case. The figures are on p. 100.
I EOT
PHOTOGRAPHIC
_>^ PLATE
IN SLIDE
^ 5 |
RICE'S EXPERIMENT. FIG. i, 106, p. 99.
Diagram.
RICE'S EXPERIMENT. FIG. 2, 106, p. 99.
Taken with the above apparatus.
101
107. SOURCE OF X-RAYS TESTED BY PROPAGATION THROUGH
A SMALL HOLE. This would illustrate not only that the fluor-
escent spot is the source of X-rays, but also that a very small
portion comes from other parts that are probably bombarded by
stray cathode rays (due to irregular surface of cathode 57) or
by reflected X-rays or cathode rays.
He tested the source of the X-rays by means of the following
arrangement of the apparatus : It will be noticed that the lead
diaphragm is quite close to the fluorescent spot. Upon holding
the sciascope on the opposite side, and pointing it toward the
spot, the luminous area of the fluorescent screen was about the
same as that of the opening in the diaphragm, but the size grew
rapidly upon receding from the diaphragm. If the rays had
come from the cathode, however, the fluorescent spot on the
screen would not have increased in size so rapidly during reces-
sion, and, therefore, the rays must have come from the spot on
the glass struck by the cathode rays. 113, 116, 117.
1070. LEEDS' AND STOKES' EXPERIMENT. USE OF STOPS IN
SCIAGRAPHY. Western Electrician, Mar. 14, '96. In order to ob-
tain clear definitions of the shadows, Messrs. M. E. Leeds and
J. B. Stokes provided lead plates with holes, varying in size from
^ inch to an inch between the discharge tube on one side and
the object and photographic plate on the other. In this manner
they obtained excellent sciagraphs of animals having very fine
skeletons. See the picture of the rattlesnake at 135 and of a
fish on page 63. See also the frog taken abroad page 90.
107^. MACFARLANE, MORTON, KLINK, WEBB AND CLARK'S
EXPERIMENT. X-RAYS FROM Two PHOSPHORESCENT SPOTS.
Elect. World, Mar. 14, '96. By means of nails projecting verti-
cally from a board (similar to the process carried out by Dr.
William J. Morton, Elect. Eng., N. Y., Mar. 5, '96), they
proved, undoubtedly, that the source of the X-rays was at the
surface of the glass directly opposite the cathode. By modifica-
tion, which acted as further proof, a tube was provided with a
cathode at the centre. There was a phosphorescent spot at
each end. One board was placed laterally to the tube, and two
shadows of each of certain nails were cast, which were caused
as proved by measurement, by a double source of X-rays. This
experiment illustrates the importance of preventing double
shadows. The plate should be perpendicular to the line joining
the two sources of the X-rays when there are two such sources.
Even with the focus tube Dr. Philip M. Jones, of San Francisco,,
determined that there were two phosphorescent spots. These
should be taken into account in all cases and attempts made to-
A PLATE I
STINE'S EXPERIMENT. FIG. i, 108, p. 103.
STINE'S EXPERIMENT. FIG. 2, 108, p. 103.
103
produce but one strong focus upon the platinum. Elect. World,
N. Y., May 23, '96.
108. STINE'S EXPERIMENTS. SOURCE OF X-RAYS DETERMINED
BY SCIAGRAPHS OF SHORT TUBES. Elect. World, N. Y., Apr. 1 1, '96,
pp. 392, 393. Prof. Stine, of the Armour. Inst. of Tech., by
means of the diagram shown in Fig. i, p. 102, clearly proved that
the X-rays have their source at the area struck by the cathode
rays located directly opposite the disk marked " cathode." If
the reader will investigate the diagram and the sciagraphs, he
will obtain a clearer knowledge of the evidence than by any
verbal description, further than to explain how the elements
are related to one another. In Fig. i, therefore, will be noticed
covered photographic plates, located as indicated with reference
to the extreme left-hand end of the discharge tube, where the
cathode rays strike. The surface of Plate 5 is parallel to that
of the cathode, and the phosphorescent spot is in line between
the two above named elements. The result is shown in Fig. 2,
p. 102, the objects sciagraphed being several short sections of
tubes with diameters varying from ^ to 3 inches.
A, in Figs. 3, 4, p. 104 and in Figs. 5, 6, p. 112, identifies the ends
lettered A in Fig. i. The sciagraph in Fig. 3 was obtained on
the plate shown at the top in Fig. i ; that in Fig. 4, on Plate 2 ;
that in Fig. 5, on Plate 3 ; and that in Fig. 6, on Plate 4. Not
only were direct shadows visible, but also secondary shadows,
indicating, therefore, that, although the source of practically all
the rays was at the phosphorescent spot, yet a portion of the
rays came slightly from other directions, either by reflection or
by actual production of rays, upon other portions of the tube.
Look now especially at Fig. 3, p. 104. If the rays came from
the anode, then would this appearance necessarily be the same
as that in Fig. 2. Similarly, the other sciagraphs may be con-
sidered to show that the rays do not come from the anode. In
the case of the sciagraphs in Figs. 4, 5 and 6, only a single tube
acted as the body for casting a shadow. Prof. Stine stated that
the experiments were repeated over and over again, thereby es-
tablishing the phenomena as uniform.
109. STINE'S ELECTRICAL APPARATUS EMPLOYED. 106, 112,
114, 131, 137. Prof. Stine gave the following suggestive points :
" Among the first points investigated was the influence of the
interrupter. The coil was provided, first with the familiar mer-
cury make and break, and then an ordinary vibrator. The
mercurial device gave very good results.
The small interrupter was found the more reliable, and
seemed to shorten the needed time of exposure. A rotary con-
10 5
tact- maker, giving two interruptions of the current per revolu-
tion, was also tested. This was driven by a motor with a con-
denser capacity of fourteen microfarads connected across the
brushes. Owing to the large capacity of the condenser, a heavy
current could be broken without marked sparking. The cir-
cuit breaker was tested at speeds ranging from 500 to 4,000 per
minute, to note the influence on the time of exposure. The
best results were obtained at the lower speed. . . . As no
especial advantage could be noted when using the mercury
breaker, it was abandoned for the vibrating interrupter." This
point is noted in detail, since so many experimenters seem to
prefer such cumbersome devices, but they are, in reality, un-
necessary.
n '
( > i
1 A
1 r
\<
,'
(
It
. ' i
_
1 1\
1 ^
STINE'S EXIERIMENT, FIG. A. no.
no. APPARENT DIFFRACTION OF X-RAYS REALLY DUE TO
PENUMBRAL SHADOWS. Elec. Eng., Apr. 22, '96, p. 408. By
referring to the diagram marked " Stine's Experiment, Fig. A,"
the arrangement of the elements may be seen, while the photo-
graphic print is shown in " Stine's Experiment, Fig. B." p. 106.
Prof. Stine described the investigation as follows : Diffraction
is naturally one of the first kinematical points to be investigated
in the Roentgen experiments. It was noticed that when the
opaque object was some distance from the plate, pronounced
penumbral shadows resulted. These were of such width as to
indicate diffraction. However, when such shadows are plotteo
back to the tube they are found to be purely penumbral, and not
io6
caused by diffraction. To completely demonstrate this point
the experiment illustrated in Fig. A was undertaken. Here Aj
to A are brass plates one inch wide and ^ inch thick, and of the
length of the dry plate employed. They were first fastened to-
gether, so as to leave two parallel slots ^ of an inch wide.
These plates are placed within 3/s of an inch of the bulb, were
one inch apart, and rested i^ inches above the dry plate. The
resulting sciagraph is shown in Fig. B. In the diagram Si S 2 ,
the edges of the penumbral shadow are very sharp and distinct.
The direction of the rays is indicated, showing that there was
absolutely no diffraction. This experiment has been modified
in a variety of tests, with always the same result."
1 100. JEAN PERRIN'S NON-DIFFRACTION. Comptes Rendus, Jan.
27, '96. From trans, by Louis M. Pignolet. The active part of
a tube was placed before a very narrow slit ; 5 cm. further,
there was a slit i mm. wide ; 10 cm. further, there was the pho-
tographic plate. An exposure of nine hours gave an image
with sharply defined borders, upon which there was no diffrac-
tion fringe.
STINE'S EXPERIMENT, FIG. B. no.
159. NON- REFRACTION. Refraction was attempted with pris-
ims of paraffine and of wax, but no refraction was noticed.
III. SCRIBNER AND M'BERTY'S EXPERIMENT. SOURCE OF X-
RAYS DETERMINED BY INTERCEPTION OF ASSUMED RECTILINEAR
RAYS FROM THE CATHODE. Elect. Eng., N. Y., Apr. 8, '96, p.
358 ; Amer. Inst. Elec. Eng., Mar. 25, '96. West. Branch. Refer
now solely to Fig. i, S. and M.'s experiment. Notice the rela-
tive arrangement of the elements. First, the discharge tube
with the cathode at the upper part and the phosphorescent spot
opposite thereto ; then below a thick lead plate with a single
opening ; then a second lead plate with two small openings
placed laterally at such a distance that if there were rectilinear
rays from the cathode they could not strike (by passing through
the small hole), the covered photographic plate which was the
next element in order. The description did not state that the
photographic plate was covered, but the experimenters must
have had the usual opaque cover upon it or else the luminous
107
rays could have produced images. The developed plate showed
two spots strongly acted upon and surrounded, by portions which
were less acted upon, the same as would be produced by light
radiating from a surface as distinguished from a point. From
the fact that they stated that the exposures were very long, it
may be concluded also that the plates were covered by a ma-
terial opaque to ordinary light. Measurement showed that the
rays which produced the images came from the phosphorescent
spot ( 1 06, 109, 114, 131, 139) and not from the cathode directly
rjy rectilinear propagation.
112. SOURCE ON INNER SURFACE OF THE DISCHARGE TUBE DE-
TERMINED BY PIN HOLE IMAGES. Reference may now be made
to S. and M.'s Experiment, Fig. 2. The discharge tube has, as
before, a cathode on one side, and the phosphorescent spot dur-
ing operation on the opposite side. Lead plates were provided
in positions indicated by the heavy black straight lines, there
S. & M.'s EXPERIMENT, FIG. i. & 2.
being a pin hole in each one. Behind these lead plates, meas-
ured from the discharge tube, were the covered photographic
plates, as indicated. By measurement, it was afterwards deter-
mined that practically all the X-rays started from the phosphor-
escent spot. The electrode was put in an oblique position, as
indicated, so that the same would not obstruct any X-rays try-
ing to pass through the pin hole in the uppermost plate. The
experiment served specifically to show that the X-rays started
from the inner surface of the glass, because images produced
on the upper and lower plates were equally strong. Perrin also
found that the X-rays are developed at the interior sides of the
tubes. (Comptes Rendus, Mar. 23, '96. From trans, by L. M. P.)
The rays, in producing each image, had to pass through an equal
thickness of glass. If the rays had come from the outer sur-
face, for example, two thicknesses would have been traversed
by the rays striking the upper plate, and no thickness by those
impinging upon the lower plate. That no rays came from any
io8
other portion or element of the discharge tube was evident,
because a picture of the phosphorescent spot was the only one
produced, and this picture was inverted, as usual, with pin
hole cameras. (A pin hole camera is the same as any other, with
the lens replaced by a very small hole, which acts as a lens.)
In the way of further evidence, if not enough already, Meslans
early determined that the phosphorescent spot on the glass
is the source of X-rays (Comptes Rendus y Feb. 24, '96. From
Trans, by Mr. Louis M. Pignolet).
JEAN PERRIN'S EXPERIMENTS. THE ORIGIN OF X-RAYS,
Comptes Rendus, Mar 23, '96. From Trans, by Louis M. Pigno-
let. He also confirmed that X-rays radiate from the phosphor-
escent spot.
1 1 20. DE HEEN'S EXPERIMENT. THE ANODE BELIEVED TO BE
THE SOURCE OF X-RAYS. Comptes Rendus, Feb. 1 7, '96. From trans,
by Louis M. Pignolet. A lead screen, pierced by several holes,
was placed between the discharge tube and the photographic
plate. The shadows of the holes on the plate indicated that
the rays emanate from the positive pole of the tube.
* As both Thomson (E.) and Rowland, as well as De Keen, at
first concluded likewise, is it not probable that the anode was
struck by the cathode rays (see 113, 116) ? For it was fully
admitted that the anode, otherwise, does not emit X-rays.
113. LODGE'S EXPERIMENT. X-RAYS MOST POWERFUL WHEN
THE ANODE is THE PART STRUCK BY THE CATHODE RAYS.
PIN HOLE PICTURES BY X-RAYS TO DETERMINE SOURCE OF
X-RAYS, AND PIN HOLE IMAGES UPON GLASS COMPARED. The
Elect., Lon. Apr. 10, '96, p. 784. The object of the experiment
was to confirm, if possible, by a modified construction, the
source of the X-rays, as being the surface struck by cathode
rays, whether the surface is that of glass or any other sub-
stance. He had constructed, for this purpose, a discharge tube,,
as illustrated in the diagram, which may be seen, at a glance,
to contain a concave electrode at one
end, and a flat electrode at the other.
Between them, and connected to the
concave electrode, is an inclined sheet
of aluminum, shading both electrodes.
The wires leading to the aluminum
sheet are well protected by glass.
He arranged matters so that either the concave or the flat elec-
trode could be made positive or negative. The operation con-
sisted first in taking through a pin hole, % f an mc ^ * n
diameter, X-ray pictures on photographic plates, from different
109
points, at measured distances. After these were taken, glass
plates received the luminous images at the positions of the
sensitive plate. Pencil drawings were then made, and com-
pared with the X-ray pictures. The experiment involved also
the repetition of this operation, except that the polarity of the
terminals was changed.
" When the small flat disk was cathode, every part of the
complicated anode appeared strongly and quickly on the plate,
especially the tilted and first bombarded portion on a photo-
graphic plate placed above the tube. The cathode disk itself
did not show at all. On a plate placed below the bulb, the
anode cup appeared strong, but the tilted disk did not appear.
On the other hand, .... its focus spot acted as a feeble
point source, by reason of a few rays reflected back on to it
from the cup.
" When the current was reversed, the small disk anode showed
faintly, being excited by rays which had penetrated the inter-
posed tilted disk, but again the cathode hardly showed at all,
not even the tilted portion on a plate placed below the bulb.
This is confirmed by J. Perrin. In no case could an image of
the cathode be obtained. (Comptes Rendus] Mar. 23, '96. From
trans, by L. M. P.) By giving a very long exposure (two hours),
some impression was obtained by Dr. Lodge about equal to
that from the shaded anode disk ; but, of course, if the tilted
plate had been under these circumtances an anode, it is well
known that a few minutes would have sufficed to show it strong
upon the plate beneath.
" Hence, undoubtedly, the X-rays do not start from the cathode
or from anything attached to the cathode,\>'&\.&Q start from a surface
upon which the cathode rays strike, whether it be an actual
anode or only an ' anti-cathodic ' surface. Best, however, if it be
an actual anode. (Independently discovered by Rowland, 116,
and Roentgen, 91."
" When the glass walls, instead of receiving cathode rays, are
pierced only by the true Roentgen rays from the disk in the
middle, no evidence is afforded by my photograph that the
glass under these circumstances acts as a source. It is well that
it does not, for its only effect would be a blurring one. 91.
With focus tubes, the glass posphoresces under the action of
the X-rays as anything else would phosphoresce, but its phos-
phorescence is not of the least use. It is a sign that a tube is
working well, and that the rays are powerful ; but if by reason
of fatigue ( 58) the glass ceases to phosphoresce strongly, the
fact constitutes not the slightest detriment."
no
X-RAY UNINFLUENCED BY A MAGNET. SEVERE TEST. His
first experiment on magnetic deflection, the sciagraph of a mag-
net with a background of wire-gauze, only showed that if there
were any shift by reason of passage of rays between the poles it
was very small ; but he definitely asserted, as in accompanying
diagram, that a further experiment has been made which effec-
tually removes the idea of deflectibility from his mind, and con-
firms the statement of Professor Roentgen. 79. A strong
though small electromagnet, with concentrated field, had a pho-
tograph of its pole-pieces taken with a couple of wires, A and C,
stretched across them on the further side from the plate nearer
the source and a third wire, B, also stretched across them, but
on the side close to the plate. These three wires left shadows
on the plate, of which B was sharp and definite, while A and C
were blurred. Two sciagraphs were taken by Mr. Robinson,
A&C
one with the magnet on, and one with the magnet reversed. On
subsequently superposing the two plates, with the sharp shad-
ows of B coincident, the very slightest displacement of shadows
A and C could have been observed, although those shadows
were not sharp. But there was absolutely no perceptible dis-
placement, the fit was perfect. Consequently the hypothesis of
a stream of electrified particles is definitely disproved as no
doubt had already been effectively done in reality by Professor
Roentgen himself. But it must be noted, he stated, that the
hypothesis of a simple molecular stream not an electrified one
remains a possibility. The only question is whether such an
unelectrified bombardment would be able to produce the ob-
served effects. It must be remembered, Dr. Lodge stated, that
Dr. Lenard found among his rays two classes as regards deflec-
tibility some much deflected, others less deflected ; and it must
Ill
be clearly understood that his deflections were observed, not in
the originating discharge tube, where the fact of deflection is a
commonplace, but outside, after the rays had been, as it were,
" filtered " through an aluminum window. He did not, indeed,
observe the deflection in air of ordinary density ; it was in mod-
erately rarefied air that he observed it, 720, but he showed that
the variation of air density did not affect the amount, but only
the clearness of the minimum magnetic deflection. The cir-
cumstance that affected the amount of the deflection was a vari-
ation in the contents of the originating or high-vacuum tube.
114. LODGE'S EXPERIMENT. APPARATUS EMPLOYED. The Elect.,
Lon., April 10, '96, p. 783. With his apparatus, he was able to
obtain rays sufficiently powerful to illuminate the usual fluor-
escent screen after passing through one's skull. It is of inter-
est to note about the details of the electrical apparatus ( 106,
109, 131, 137) used by those who experimented. The best results
were obtained by a make and break of a direct primary current at
a point under alcohol, the primary battery consisting of three stor-
rage cells, and the current of the primary acting on a large sec-
ondary coil. Leyden jars he considered entirely unnecessary, and
he preferred direct currents to alternating currents for the pri-
mary. He did not give the exact dimensions of the primary and
secondary coils, but, judging from reports of others and the au-
thor's own experience, it is highly preferable to have what is
called a very large inductorium, 15 in. spark in open air, or
else the Tesla system ( 51, 137). There is little satisfaction in
trying to perform the experiments with induction coils adapted
to give only a 2 or 3 in. spark in open air.
115. LODGE'S EXPERIMENT. X-RAYS EQUALLY STRONG DURING
FATIGUE OF GLASS BY PHOSPHORESCENCE. The Elect., Lon., Apr.
10, '96. In order to explain in what way the rays were propa-
gated, he says that it is not as if the glass surface were a wave
front from every point of which rays proceed normally, but
that the glass radiates X-rays just as a red-hot surface radiates
light, namely, a cone of rays starts from each point, and all the
rays of each cone start in a different direction. Every point
of the glass radiates the rays independently of all other
points. Crooke's Experiment ( 58) may now be called to
mind in reference to the fatiguing of the glass after phosphor-
escing for a while. Lodge tested the fatiguing as to the power
to emit X-rays, but found that there was no such property
whatever. The glass which became fatigued as to luminous
phosphorescence ( 105) was not fatigued as to the power of
X-rays. He noticed that the phosphorescent spot became less
.and less bright, and yet the X-rays remained of the same power.
116. ROWLAND, CARMICHAEL AND BRIGGS' EXPERIMENT.
AREA STRUCK BY CATHODE RAYS ONLY AN EFFICIENT SOURCE
WHEN POSITIVELY ELECTRIFIED. Electricity p , N. Y., Apr. 22, '96,
p. 219. Experiments carried on at the Johns Hopkins Univer-
sity led the above named investigators to think at first that the
source of the X-rays was at the anode. Amer. Jour. Sci., March,
'96. Prof. Elihu Thomson was led to give the same opinion
during his first experiments. Elect. Rev., N. Y., Mar. 25, '96.
See also 1 1 20 . Many other experiments certify to the allega-
tion that X-rays are certainly generated at the phosphorescent
spot on the glass. 79, 105, 107, 108, in, 112, 113. From the
experiments of Prof. Rowland, et al., the confusion is accounted
for by the fact that they overlooked the electrical condition of
the spot struck by the cathode rays. Prof. Rowland, et at., con-
structed a tube having a platinum sheet located at the focus of
the concave electrode, and not connected to the anode. Al-
though the platinum became red hot, it emitted no X-rays, but
when the platinum was made the anode, there was profuse radi-
ation of X-rays in all directions from that side of the platinum
.struck by the cathode rays, and no radiation from the other side.
91. (See also Roentgen and Tesla, concerning YZ platinum
and y* aluminum and radiation therefrom.) They inferred as a
final conclusion in connection with this point, " That the neces-
sary condition for the production of X-rays is an anode bom-
bardment by the cathode discharge." 113. They recognized
apparently that it had been conclusively proved that X-rays ra-
diated from the phosphorescent spot on the glass. They held
that such a spot is " The induced anode formed on the glass."
49, at end. They did not prove this by an experiment accord-
ing to the article referred to, but based it upon " The fact that
the bombarding cathode rays coming in periodical electrified
showers alternately raise and lower the potential of the glass,
thus making it alternately an anode and a cathode. In the case
of the platinum, this could not occur to the same extent."
117. SALVIONI'S EXPERIMENT. TRANSPOSITION OF PHOSPHOR-
ESCENT SPOT. Elect. Rev., Lon., Apr. 24, '96, p. 550 ; Med. Sur.
Acad., of Perugia, Italy, Feb. 22, '96. Personal interview with
Prof. Salvioni in Elect. Rev., N. Y., Apr. 8, '96, p. 181. In order
to change the location of the phosphorescent spot when desired,
without a magnet, and at the same time to concentrate or inten-
sify the source of X-rays, he placed near the same, on the out-
side of the tube, the hand or a metal mass connected to earth.
H4
The spot immediately jumped to the other side of the tube, 49,
near centre, and to all appearances was smaller and brighter.
Elster and Geitel had performed similar experiments at an
earlier date. (See Wied. Ann., LVI., 12, p. 733, also Elect. ng.,
about April, '96.) They carried on the most minute investiga-
tions as to the deflection of the cathode rays by an outside
conductor. Tesla had also noticed a similar deviation. Sec
Martin's Tesla's Researches. He used alternating currents as
described in his system in 51. Elster and Geitel used the
Tuma Alternating system. (See Wied. Ann. y Ber. 102, part 2A,
p. 1352, '94.) The source from which Salvioni's description was
taken had no sketch, therefore the diagram made by Elster and
Geitel is reproduced. See Fig. i. The cathode was aluminum
and was connected to one terminal of the transformer. The
anode was connected to earth, and also was the other terminal.
Upon bringing the hand or other conductor connected to earth
to the phosphorescent spot, the cathode rays deviated and the
spot jumped over to the other side. 50. The anode was a
ring surrounding the leading-in wires of the cathode, and the
two leading-in wires were surrounded by glass. It may be
asked why the cathode rays bent downward in the first place ?
Elster and Geitel found that they were thrown thus in view of
the nearness of some neighboring object connected to earth.
To overcome the action of surrounding objects, the tube was
surrounded by a ring as shown in Fig. 2. However, the rays
were still sensitive to objects well connected to earth, and when
brought quite close to the tube.
1170. HAMMER AND FLEMING'S MOLECULAR SCIAGRAPH, WITHIN
A VACUUM TUBE. (Citations below.) In view of the overwhelm-
ing evidence concerning the generation of X-rays by the im-
pact of cathode rays, within a high vacuum upon the glass or
material which preferably forms the anode, it becomes appro-
priate, it is thought, to review the state of this department of
science, in order to arrive a little more closely at the relations
which exist between phenomena of low and high vacua. With
the former, in that condition in which striae are formed, perma-
U5
nent black bands or deposits are produced upon the surface of
the glass; the motion of the particles, therefore, appearing to
be in planes at right angles to the line joining the anode and ca-
thode. 40. That the striae should touch the walls of the tube
seems to be necessary for the production of the deposit. 44.
With a high vacuum, the direction of the cathode rays
may be any that one desires, it being only necessary to shape
the cathode properly, on the principle that the rays radiate
normally from the surface. It is known that the radiation is
normal as much from the position of the deposit as from that
of the phosphorescent spot. It is certain that they are rectilinear.
57 and 58. The phosphorescent spot becomes always, sooner
or later, when occurring upon the same part of the glass, the
location of a deposit from the cathode ( 123), even when
the cathode is aluminum. 123. The deposit is not the cause
of the fatigue of the glass. 58. Puluj verified this. A
wheel was made to rotate by the radiations from the cathode,
and therefore it is highly probable that the motion of the mole-
cules, which caused the deposit, is the force that made the
wheel rotate. 580. Why does it not follow that with increase
of E. M. F. the particles are thrown with such rapidity that upon
striking the proper surface ( 80), X-rays are generated, but
that they are not generated when the velocity of the molecules
is insufficient. 6i, p. 46. Attention is now invited to a phe-
nomenon which illustrates that a permanent sciagraph of ob-
jects may be impressed upon the inner surface of a vacuum
tube, by the deposit of molecules of one of the electrodes.
Refer, therefore, to the figure on page 30, " Hammer and
Fleming's Molecular Sciagraph." As will be seen from further
explanation and from the picture itself, the sciagraph a b is
made because of the projection, in rectilinear lines, of mole-
cules of carbon or metal, from one of the electrodes, or at
least from one more than the other. One leg of the carbon, be-
ing in the way of the other, causes a less deposit to be produced
upon the glass at the intersection of the plane of the horse-
shoe filament and the wall of the vacuum tube. Electrodes
exist because the filament is of such a high resistance as to
produce a difference of potential between the two straight
lower portions of the filament. Mr. William J. Hammer pos-
sesses a remarkable faculty for observing phenomena often
overlooked by others. He first observed a molecular shadow
in 1880 and made records of his observations in the Edison
Laboratory note book. Since that time he has examined over
600 lamps, which were made at various periods during thirteen
u6
or fourteen years, by twelve different manufacturers. (Trans.
Amer. Inst. Electrical Eng., Mar. 21, p. 161.) Every one, more
or less, exhibited the molecular shadow. It is a principle,
therefore, that if the carbon filament has both legs in the same
plane, a sciagraph of one of them will be produced. As the
shadow is on one side of the bulb only, the molecules fly off
from only one electrode, viz.. the cathode. By means of
photography, the effect is increased because of certain well-
known principles. The figure heretofore referred to is taken
from a photograph, but, of course, does not represent the sci-
agraph as well as the original photograph, in view of the loss
of effect byre-production by the half-tone process. For further
theoretical considerations, see the Institute paper referred to,
where the matter was discussed by Profs. Elihu Thomson,
Anthony and others. Independently of Mr. Hammer's discovery,
Prof. J. A. Fleming, professor of electrical engineering in the
University College, London, England, discovered and studied
the matter, and presented it before the Phys. Soc. of London,
appearing about 1885 (from memory]. The name " molecular
sciagraph " is given by the author because it is an accepted ex-
planation that the deposit is due to either molecules or atoms of
the electrode, given off by evaporation (page 46, lines 5 to 10),
or electrical repulsion ( 6i#, lines 22 to 25), or, as some hold,
by mere volatilization by the intense heat of incandescence, or
one or more combined ; but electrical repulsion certainly has
something to do with the rectilinear propagation, for the mole-
cules are charged according to 4.
CHAPTER X.
1 1 8. EDISON'S EXPERIMENTS. CHARACTERISTICS OF DISCHARGE
TUBE, PHOTOGRAPHIC PLATES, ELECTRICAL APPARATUS, FLU-
ORESCENCE, ETC. Elec. Eng. y N. Y., Feb. 19, '96; Mar. 18 and
25 ; Apr. i, 8, 15 and 29, '96. X-RAYS BEGIN BEFORE STRIAE
END. The reader may remember a former section, 10, point-
ing out that striae were usually obtainable without very high
vacua, and that phosphorescence of the glass occurs only with
high vacua. 54. In carrying the vacuum up higher and
higher, Edison observed that feeble Roentgen rays were de-
tected before the striae ceased. Prof. Elihu Thomson indepen-
dently performed a like experiment and found that the Roentgen
rays could be obtained even when the vacuum was so low as to
produce striae. (Elec. Eng.> N. Y., Apr. 15, '96.) Victor Chabaud
and D. Hurmuzescu also obtained X-rays from a vacuum .025
mm., being lower than Crookes employed, which was at a max-
imum .coi mm. (L? Industrie Elect. , Paris, May 25, '96. From
trans, by Louis M. Pignolet.)
119. REASON WHY THIN WALLS ARE BETTER THAN THICK.
X-RAYS AND POST-PHOSPHORESCENCE. This may be understood
by explanation of the discharge tube in Fig. i. In one experi-
ment, the portion struck by the cathode rays, namely B, was
made ^6 inch thick. It became soon hot and very luminous and
melted, 61, but the X-rays were weak. When blown thin,
( 83) however, the glass remained cool and the X-rays were
much stronger. What is known on the market as German glass
(phosphoresces green, 55, at centre) was found more permeable
than lead glass, the thickness of the walls being the same in
both cases. There were no lingering X-rays from after-phos-
phorescence, ( 54, at end) or, if any, could not be detected by
the sciascope. The photographic test would be objectionable
because of the brief duration. Prof. Battelli and Dr. Garbasso,
of Pisa, made a very sensitive test in this connection, proving by
the discharge of an electrified body ( 90 and 900) that feeble
X-rays were emitted after the current was cut off from the dis-
charge tube. (From trans, by Mr. Pignolet.)
117
n8
120. To PREVENT PUNCTURE OF THE DISCHARGE TUBE BY
SPARKS. In the illustration, Discharge Tube Fig. 2 shows a
suitable type. It is drawn to scale, showing the correct propor-
tion of the length to the diameter. The shaded ends represent
tinfoil on the outside and connecting with the leading-in wires,
DISCHARGE TUBE, FIG. 3. 120.
DISCHARGE TUBE, FIG i. 119.
the same preventing puncture of the glass by the spark. They
may be caused to adhere by shellac or similar glue. In place of
the metallic coating detached supplementary electrodes may be
employed, as seen in the illustration marked " Discharge Tube
Fig. 3." The power of the X-rays was increased, being due, it
H9
was thought, to the fact that the construction embodied the
combination of internal and external electrodes. 121.
121. VARIATION OF VACUUM BY DISCHARGE AND BY REST.
Prof. Pupin was among the first to test the efficiency of exter-
nal electrodes for generating X-rays. Independently of the
quality of the glass and of the kind of pump and of the pres-
ence or absence of phosphoric anhydride, the following peculi-
arities were noticed, which Edison attributed to a kind of atomic
electrolysis. 47. So per cent, of the lamps exhibited the
phenomena as follows: First, such a high vacuum was obtained
by the pump that the line spectrum disappeared and pure fluor-
escence and generation of X-rays at a maximum occurred.
The lamp was then sealed off. After three or four hours of
rest, the vacuum deteriorated, so that striae and other charac-
teristics of low vacuum were obtained when connected up in
circuit, but upon continuing the current, the high vacuum grad-
ually came back, the line spectrum vanished, and suddenly
X-rays were generated. Again the bulb was left at rest for
DISCHARGE TUBE, FIG, 2. 120.
24 hours, after which X-rays coulu not be generated until the
discharge had been continued for 4^ hours.
122. EXTERNAL ELECTRODES DISCHARGE THROUGH HIGHER
VACUUM THAN INTERNAL. A vacuum that was so high .that no
discharge took place with internal electrodes was made lumi-
nous by the use of electrodes on the outside of the glass bulb.
Then he made the vacuum so high that even with a 1 2-inch
spark from Ley den jars, no discharge took place with external
electrodes, and the tube was dark, this part of the experiment
indicating another limit at which an extremely high vacuum is
not a conductor and appearing to overthrow, as Edison inti-
mated, Edlund's theory that a vacuum is a perfect conductor.
35.
123. DEPOSIT ON GLASS FROM ALUMINUM ELECTRODE. It
has always been common to employ aluminum for electrodes in
vacuum tubes, on the ground that no deposit took place, and
therefore no blackening, nor whitening of the glass wall. 40.
Edison observed also that no blackening was visible, but stated
that his glass blower, Mr. Dally, upon breaking the bulb and
submitting the interior surface of the glass to an oxydizing
120
process, the oxide of aluminum was so thick as to be opaque to
light. With magnesium, also, a mirror was produced, of a
lavender color, by transmitted light. In the case of aluminum,
he was able to obtain a visible spot at the phosphorescent por-
tion, but only after a great many hours of use. See cut from a
photograph of a discharge tube used for several months by
Prof. Dayton C. Miller, and having a heavy aluminum deposit
opposite the aluminum cathode. With the increase of the
deposit, the power of the X-rays diminished, but, he thought,,
not on account of the absorption, but because, " through lack of
elasticity at the surface."
124. FLUORESCENT LAMP. In an English patent of '82, granted
to Rankin Kennedy, there is described a vacuum bulb in which
DISCHARGE TUBE, 123.
the electrodes are covered with fluorescent or phosphorescent
substances, intended for the purpose of obtaining greater candle
power by impact of cathode rays upon anode of platinum,
covered with alumina or magnesia. Edison coated the inner
wall of the discharge tube, for generating X-rays, with calcic
tungstate in the crystaline form. The luminosity, when meas-
ured, amounted to about 2^ c. P. As to the efficiency, he
stated that this was accomplished " with an extremely small
amount of energy." Such a coating was found to weaken the
X-rays radiated therefrom, which, of course, was natural, be-
cause they had been converted into phosphorescent light. The
spectrum showed strongly at the red line, thereby suggesting
the reason why the light was of a pleasant character.
121
PILTCHIKOF'S EXPERIMENT. Greater emission of X-rays
by a tube containing an easily fluorescent substance. Comptes
Rendus, Feb., 24, '96. From trans, by Mr. Louis M. Pignolet.
As the X-rays emanate from the fluorescent spots on the glass
of the discharge tube, he reasoned that more powerful effects
would be obtained by replacing the glass by a more fluorescent
material. He therefore tried a Puluj tube and found that it
shortened the time necessary for taking a photograph in a
''singular" degree. Experiments of others have certainly shown
that as phosphorescence decreases with increase of vacuum, the
X-rays increase to a certain maximum 105. Let it be noticed
however, that this does not prove that with the same vacuum,
an increase of phosphorescence by a superior phosphorescent
material of equal thickness would not increase the power of the
X rays. The best way to determine such points, is to go to ex-
tremes. Edison applied so much easily phosphorescent material
(calcic-tungstate) to the inside of the discharge tube, that much
light was radiated, but only feeble X-rays. On the other hand,
without any of the tungstate, the rays were strong, 1 24. Ex-
periments generally tend to prove that it depends upon the
chemical nature of the material rather than its phosphorescing
power, in other words upon the permeability. 119, near end.
125. ELECTRODES OF SILICON CARBIDE. (Carborundum.)
Edison called attention to Tesla's discovery that this substance
is a good conductor for high tension currents. Its advantages
for electrodes in the discharge tube are its high conductivity, no
absorbed nor released gas bubbles, and its infusibility and non-
blackening power of glass even when the voltage was increased
to a point where the glass melted.
126. CHEMICAL DECOMPOSITION OF THE GLASS BULB. During
the generation of the X-rays the sodium line of the spectrum
appeared in the spectroscope, thereby indicating decomposition
of the glass. With combustion tubes the glass gave the weakest
soda line, while lime soda glass gave the strongest, and was most
permeable to the X-rays. "The continuous decomposition of the
glass makes it almost impossible to maintain a vacuum except
when connected to the pump and even then the effect of the
current is greater in producing gas than the capacity of the
pump to exhaust, but the ray is very powerful." It is supposed
that for this reason, as well as for others easily apparent that
Edison as well as other experimenters have always carried on
their investigations with the discharge tube permanently con-
nected to the pump. The next best thing is to let the tube con-
tain a stick of caustic potash for maintaining an exceedingly
EDISON (AT RIGHT) AND T. COMMERFORD MARTIN USING THE SCIASCOPE.
97, p. 84.
Cut also shows Sprengel vacuum-pump. Discharge-tube is in the box.
high vacuum. By gradually heating this, the desired degree of
vacuum can be obtained. 54.
127. SCIAGRAPHS. DURATION OF EXPOSURE DEPENDENT UPON
DISTANCES. With the given discharge tube, he obtained scia-
graphs at a distance of ^4 inch from the phosphorescent spot in
one second, a vulcanized cover being between ; at two ft, dis-
tant the time was 150 sec.; at three ft, 450 sec.; the opaque
plate being interposed each time. Consequently "Roughly, the
duration of exposure may be reckoned as proportional to the
square of the distance."
128. DIFFERENCE BETWEEN X-RAYS AND LIGHT ILLUSTRATED
BY DIFFERENT PHOTOGRAPHIC PLATES. TIME OF EXPOSURE.
The rapid plate for light gave not the deepest images by X-rays.
Several different kinds of small sensitive plates were laid side
by side. A sciagraph of a metal bar was taken upon them all
simultaneously. In this way, he obtained the result, whereby
it would appear preferable to employ the mean rapid plate for
the purpose of obtaining sciagraphs. On account of the opacity
of platinum, it occured to E. B. Frost, (Sci., N. Y., Mar. 27, '96,)
to try platinum photographic paper of the kind used for portraits,
but such paper (intended for long exposures in printing in sun-
light) was far too lacking in sensitiveness to produce any effect.
i2&a. GEORGES MESLINS INSURED A REDUCTION OF TIME FOR
TAKING SCIAGRAPHS BY THE DEFLECTION OF THE CATHODE RAYS
BY MEANS OF A MAGNETIC FIELD. Comptes Rendus, March 23 and
30, 1896. From trans, by Louis M. Pignolet. The method con-
sists in using a permanent or electro magnet to create a mag-
netic field perpendicular to the cathode rays in the tube. By
this means, the active fluorescent spot on the tube is condensed,
and the intensity of tlie X-rays generated there is increased.
Another advantage is that, when the active part of the tube be-
comes inactive owing to the formation of a light brown deposit
upon it, another part can be used by very slightly altering the
position of the magnets. Thus, each time a new part of the tube
can be used. The magnetic field must not be uniform but must
have a suitable variation to produce the desired concentration
of the cathode rays.
A. IMBERT AND H. BERTIN-SANS' EXPERIMENT. (Comptes
Rendus, March 23, '96. (From trans, by L. M. P.) They short-
ened the time by use of a magnet.
JAMES CHAPPIN'S EXPERIMENT. (Comptes Rendus, Mar. 30, '96.
(From trans, by L. M. P.) Claimed priority in having shown
publicly, on Feb. 19, a sciagraph of a hand, marked " Photograph
obtained by concentration of the cathode rays, by means of a
I2 4
magnetic field." The increase of the intensity of the X-rays
obtained by this means was in the proportion of 8 to 5, as meas-
ured by the time of fall of the leaves of a Hurmuzescu elec-
troscope.
Prof. Trowbridge, of Harvard University, in a lecture, gave
an interesting review (Western Elect., Feb. 29, '96) of the length
of time required in the early days of photography. Improve-
ments are being made whereby the duration required in scia-
graphy becomes less and less. In 1827, by heliography, 6 hours'
exposure was necessary; in 1839, by daguerrotype, 30 minutes;
in 1841, by calotype, 3 minutes; in 1851, by collodion, 10 seconds:
in 1864, by collodion, 5 seconds; in 1878, by gelatine, i second.
The author remembers the photographs for use in the Edison
kinetoscope were taken at the rate of 20 per second. The focus
tube brings the time of exposure in behalf of X-rays down to
a matter of seconds instead of minutes. For an admirable re-
view of authorities, facts and theories relating to the causes of
the darkening of photographic plates by light, see Cottier, in
Elect. World, N. Y., May 23, '96.
129. SIZE OF DISCHARGE TUBE TO EMPLOY FOR GIVEN APPA-
RATUS. A small tube required but a small E. M. F., and there-
fore should be employed with a small induction coil. The
greater the distance of the sensitive plate and the object, con-
sidered together, from the discharge tube, the sharper the
shadow. In short exposures, the tube should be small and at a
short distance.
130. PREVENTING PUNCTURE AT THE PHOSPHORESCENT SPOT.
In experiments where he employed a flat cathode, a very
thin pencil of rays of increased power came from the exact
centre, and in two or three seconds made the glass red hot at
the centre of the phosphorescent spot. Immediately, the at-
mospheric pressure perforated the bulb. This occurred several
times. He stated that " the best remedy is to permit the cen-
tral ray to strike the glass at a low angle ; this greatly increases
the area and prevents the trouble." EDISON.
Mr. Ludwig Gutman furnished a translation of a note by
Prof. Walter Konig, found in Eleck. Zeit. of May 14, '96, relating
to this same subject matter. Recognizing that the sharpness
of the outlines is the most important requirement in connec-
tion with sciagraphy, and that if the rays start from a large
surface the impressed shadows will be uncertain in configura-
tion, and noticing, as Edison and Tesla did, 130, the frequent
destruction of the tube at the place where the rays were concen-
trated to a focus, he placed over the inner surface of the glass,
125
aluminum foil for distributing the heat over a larger area, at
the same time causing radiation of X-rays from a single point.
The focus tube outweighs this in importance. 91.
131. ELECTRICAL DIMENSIONS OF APPARATUS. The best kind
of instruction for the student in reference to equipping a plant
is to follow the construction employed by those who have been
successful. 1 06, 109, 114, 137. Edison used the usual incan-
descent lamp current, voltage at no to 120 volts, current being
continuous, but not connected directly to the induction coil,
there being a bank of eight to twenty 16 candle power incan-
descent lamps arranged in parallel. The interrupter for the
primary consisted of a rotating wheel in appearance like a com-
mutator of a dynamo, and was rotated rapidly by a small electric
motor, making about 400 interruptions per second, and so con-
structed that the circuit was closed twice as long as it was open.
A sudden interruption was caused by an air blast playing at the
point of make and break, the use of which made that of a con-
denser needless. 3. The discharge tube terminals were con-
nected respectively and directly to those of the secondary.
Prof. Pupin, Columbia Univ. N. Y. (Lect. N. K., Acad. Sci.,
April 6, '96, and Science, N. Y., April 10, '96) gave valuable and
practical instruction concerning the apparatus, which the author
witnessed. "A powerful coil was found indispensable for strong
effects and satisfactory work. The vibrating interrupter is too
.slow and otherwise unsatisfactory, and it was replaced by a ro-
tary interrupter, consisting of a brass pulley, 6 inches in diameter
and i^ inches in thickness. A slab of slate ^ inch thick was
inserted and the circumference was kept carefully polished.
This pulley was mounted on the shaft of a Crocker-Wheeler }i
H. p. motor giving 30 revolutions, and, therefore, 60 breaks per
second. Two adjustable Marshall condensers of three micro-
farads each were connected in shunt with the break, and the
capacity adjusted carefully until the break-spark was a mini-
mum and gave a sharp cracking sound. Too much capacity
will not necessarily increase the sparking, but it will diminish
the inductive effect which is noticed immediately in the dimin-
ished intensity of the discharge. A powerful coil with a smoothly
working rotary interrupter will be found a most satisfactory
apparatus in experiments with Rontgen radiance." 106, 109,
i'4, 131, 137-
132. SALTS FLUORESCENCE BY X-RAYS See also, Elect. Rev.,
N. Y., April 19, '96, p. 165. Edison examined over 1800 chemi-
cals to detect and compare their fluorescent powers if any, under
the action of X-rays first transmitted through some opaque
126
material such as thick cardboard. Of all these, calcic tungstate
by measurement, fluoresced with six times the luminosity of
barium platino cyanide, which was referred to in connection
with Roentgen's experiment. Other authorities agree as to its
great sensitiveness. In making this comparison, it was assumed
that the power of the X-rays varied inversely as the square of
the distance from the discharge tube. Between the two above
chemicals came strontic tungstate. Baric and plumbic tungstate
scarcely fluoresced. Salicylate of ammonium crystals equalled
the double cyanide of platinum and barium, and differed there-
from in that the fluorescence increased with the thickness of the
layer of crystals up to % of an inch, showing great fluorescing
power and low absorptivity. This experiment showed that the
best fluorescent materials were not necessarily the salts of the
heaviest metals, like platinum. It is assumed that the reader
knows the difference between phosphorescence and fluorescence,
but the dividing line is so difficult in some cases and the one
not being distinguished from the other by experimentei s, that
the author has used the same words as the experimenters,
although he admits that fluorescence is often meant where
phosphorescence is stated, and vice versa. An anomaly presented
itself as to rock salt, which although transparent to light yet
powerfully absorbed X-ray sand was strongly fluoresced thereby.
Again, fluorite which is transparent to light, fluoresced strongly
with the X-rays, and under their action became brighter and
brighter and continued after cutting off the X-rays, the material
therefore, being highly phosphorescent, the light enduring for
several minutes. Upon v/atching the phosphorescence of fluor-
ite, the same penetrated the plate very slowly to the depth of
one-sixteenth of an inch, but beyond that depth there was com-
plete darkness. The only other truly phosphorescent substance
noticed was calcic tungstate, especially in thick layers, so that
the shadow of the bones of the hand remained thereon for a
minute or two upon cutting out the discharge tube from the
circuit. Some chemicals, within a dark box and very close to the
discharge tube, phosphoresced by giving spots here and there,
but they did not phosphoresce at a greater distance, and the
light was probably not due to the X-rays. Edison attributed
the result directly to the "electrical discharge." . The list is as
follows : ammonium sulphur cyanide, calcrc formate, and
nitrate, ferric citrate, argentic nitrate, calcic and iron citrate,
soda, lime, "zinc, cyanide" (perhaps this means cyanide of zinc),
zinc hypermanganate, and zinc valeriate. The salts of the fol-
lowing metals did not fluoresce under the influence of the
128
X-rays. Aluminum, antimony, arsenic, boron, beryllium, bis-
muth, arium, chromium, cobalt, copper, gold, iridium, magnes-
ium, manganese, nickel, tin, and lithanium.
Edison stated that the following substances were among those
which fluoresced more or less under the action of the X-rays.
Mercurous chloride, mercury diphenyl, cadmic iodide, calcic
sulphide, potassic bromide, plumbic tetrametaphosphate, potas-
sic iodide, plumbic bromide, plumbic sulphate, fluorite, powdered
lead glass, pectolite, sodic cressotinate, ammonic salicylate, and
salicylic acid. Compared with the above, the following fluor-
esced less. Powdered German glass, baric, calcic and sodic
fluorides, sodic, mercuric, cadmic argentic and plumbic chlorides,
plumbic iodide, sodic bromide, cadmic and "cadmium, lithia
bromide, mercury, cadium sulphate" uranic sulphate, phosphate,
nitrate, and acetate, molybdic acid, dry potassic silicate, sodic
bromide, wulfenite, orthoclase, andalucite, herdinite, pyromor-
phite, apatite, calcite, danburnite calcic carbonate, strontic
acetate, sodic tartrate, baric sulphobenzoic calcic iodide, and
natural and artificial ammonium benzoic. Not one of all the
1800 crystals and precipitates fluoresced through a thick card
board under the influence of the arc light, 16 inch spark in air,
a vacuum tube so highly exhausted that a 10 inch spark left it
dark, nor the direct rays of the sun at noon time. As calcic
tungstate was phosphorescent by friction, he theorized that the
X-ray is a wave due to concussion.
Flame sensitive to X-rays. Edison stated that his assistants
submitted the sensitive flame and the phonographic listening
lube to the action of the X-rays, and found that they were re-
sponsive thereto.
133. X-RAYS APPARENTLY PASSED AROUND A CORNER. Refer-
ring to the figure "X-ray Diffusion Fig. i", p. 129, it will be
noticed that there were three principal elements. First a dis-
charge tube, then a thick steel plate and then a sciascope, all
arranged in the proportion indicated in the figure, where the
sciascope was within six inches of the edge of the plate, ''well
within the shadow" thereof. 69. Fluorescence was seen under
these conditions. When the sciascope was directly behind the
middle of the plate and opposite the discharge tube, there was
no fluorescence, showing that the plate was thick enough to cut
off all the rays and therefore the energy must have traveled in
two directions for some reason or other.
Prof. Elihu Thomson remarked concerning this experiment
that he considered, in view of some experiments of his own, on
diffusion and opalesence ( 103), that the sciascope was lumi-
129
nous in view of reflection ( 146) of the X-rays from various
objects in the room, as from the walls and floor of the room,
tables, metal objects, electrical apparatus and so on. Theory
admits the property of diffraction, which would cause the rays
to turn around the edge of the plate, according to the princi-
ples of diffraction of light, provided the X-rays were due to
transverse or longitudinal or any vibrations. See Elect. Eng.,
N. Y., April 15, p. 378.
While Edison generally devotes his energy to actual experi-
ments and dealings with facts and principles, rather than with
theories, yet, in this instance, he merely suggested that the flu-
orescence under the conditions named might indicate that the
propagation of X-rays was similar to that of sound in air, the
wave being of exceedingly short length. He referred to Le
Conte's experiment of '82 (see Phil. Mag., Feb. '82), where an
v \\\ - / -^-^ff-Tluoroscofrez..^
X-RAY DIFFUSION, FIG. i, 133.
experiment of a somewhat similar nature was performed in
connection with the propagation of sound.
Prof. William A. Anthony (see Elect Eng., Apr. 3, '96, p.
378) held that the Le Conte experiment did not warrant
Edison's conclusion, for the experiment of Le Conte showed
comparatively sharp sound shadows ; for even at a distance of
twelve feet there was no apparent penetration within the geo-
metrical boundary. He referred to Stine's, no; Scribner and
M'Betty's, 1 1 1, as upholding rectilinear propagation. While he
did not explain what the Edison result was due to, yet he ar-
gued that the cause was other than that ascribed by Edison.
In this connection, the author performed an experiment (Elect.
Eng., Apr. 22, '96, p. 409) to substantiate that X-rays were
propagated through such a high vacuum that it was necessary
1 3 o
to have electrodes within }6 of an inch of each other, in order
to obtain a discharge with a coil that gave 15 in. spark in open
air. The experiment consisted in casting the shadow of an
uncharged tube upon the screen of a sciascope. The shadows of
the wire forming the electrodes within the vacuum were pro-
duced very sharply, while the glass tube was faintly outlined.
Inasmuch as the shadows of objects within the vacuum tube
were obtained, therefore the X-rays must have passed through
the evacuated space. Sound and X-rays are therefore dissimilar.
The shadows were as sharp and as dark as those made by simi-
lar wires in open air. In this connection, see also Lenard's
experiment, 72, showing that external cathode rays were also
transmitted by a vacuum in a " dead " tube. Roentgen's experi-
ment showed that X-rays from a mass located entirely within
the vacuum in the discharge tube radiated X-rays into the out-
side atmosphere. 91. This experiment would hardly prove,
however, that X-rays, after having been liberated in open air,
would pass through a second vacuum space, because there may
have been some X-rays, generated at the surface of the glass in
Roentgen's experiment, struck by those rays which radiated
from the mass at the centre of the vacuum space. Did not
Lenard and Roentgen experiment with the same radiant
energy? The author answers, yes. 77.
134. PERMEABILITY OF DIFFERENT SUBSTANCES. Lenard 68,
determined the permeability of several substances to cathode
rays. Roentgen also the same in regard to X-rays. 82 and 83.
Others have made comparisons. From the sciagraph made by
Edison, the following classification is made, each sheet of
material being about -^ inch thick. The most opaque were coin
silver, antimony, lead, platinum, bismuth, copper, brass, and
iron, which were about the same as one another. Slate, ivory,
glacial phosphoric acid shellacked, and gutta percha, were about
the same as one another and less than the above. Aluminum,
tin, celluloid, hard rubber, soft rubber, vulcanized fibre, paper,
shellac, gelatine, phonographic cylinder composition, asphalt,
stearic acid, rosin, and albumen, were about the same as one
another and less than the above group, as to permeability.
The accompanying picture, p. 6, marked Terry's Sciagraph,
Fig. i, is a sciagraph of pieces of different materials named as in
the following list, taken by Prof. N. M. Terry of the U. S. N. A.,
see also p. 127. "i, rock salt, 0.6 inch thick ; 2, cork, 0.4 inch
thick ; 3, quartz, 0.45 inch thick, cut parallel to optic axis ; 4, verre
trempe, 0.4 inch thick; 5, glass, 0.7 inch thick; 6, chalk; 7, Ice-
land spar; 8, mica, very thin; 9, quartz, over a square piece of
glass; 10, aluminum foil, [a] four thicknesses, [b] two thicknesses,
[f] one thickness; n, platinum foil; 12, tourmaline; 13, aragon-
ite ; 14, paraffine, 0.4 inch thick. 15, tin foil, [a] one thickness,
\b\ two thicknesses, [c] three thicknesses ; 16, rubber insulated
wire; 17, electric light carbon; 18, glass, 0.32 inch thick;
19, alum., 1.4 inch thick; 20, tourmaline; 21, gas coal; 22, bee's
wax ; 23, pocket-book, 10 thicknesses of leather ; 24 coin in
pocket-book; 25, key in pocket-book; 26, machine oil in ebonite
cup; 27, ebonite, 0.25 inch thick; other samples have given very
faint shadows like wood and leather ; this was polished ; 28,
wood, 0.2 inch thick; 29, steel key." Elect. ng., N. Y.
1340. HODGES' EXPERIMENT. ILLUSTRATION OF PENETRATING
POWER OF LIGHT. Elec. Eng. y N. Y., March 4, '96, Attention
has been invited in the scientific press to the penetrating power
of heat rays and of light rays of low refrangibility. In conjunct-
ion with this, let it be remembered that the photographic plate
has the property of being impressed practically, only by rays
having a higher refrangibility than red. It would be natural,
therefore, to conclude that if the spectrum could be turned
around, the photographic impression might be produced through
opaque bodies. This perhaps, was the kind of reasoning which
prompted Mr. N. D. C. Hodges, formerly editor of Science^ to
perform an experiment, the gist of which consisted in attesting
the permeability of rays of light which had been passed through
fuchsine. Christiansen, Soret and Kundt performed experi-
ments with an alcholic solution of this material and found that
the order of the colors in the spectrum was somewhat reversed,
namely, violet was the least refracted, then red, and then yellow,
which was the most refracted. Mr. Hodges used a pocket
kodak, carrying a strip for twelve exposures. This camera was
placed in a closely fitting pasteboard box. Thus protected, some
portions of the film were exposed to sunlight, so far as it could
penetrate the end of the pasteboard box, while other exposures
were made with a prism, on the end of the box, containing an
alcoholic solution of fuchsine. The portions of film exposed to
the anomalous rays produced by the fuchsine solution were
fogged, while the control experiments with ordinary light showed
none. The anomalous rays must have penetrated the paste-
board, and probably the wood and leather of which the camera
was made.
135. PENETRATING POWER OF X-RAYS INCREASED BY REDUCTION
OF TEMPERATURE. 23 and 72^ at end. Among the hundreds
of ideas that occured to Edison in connection with Roentgen
ray tests was that concerning what might happen by cooling the
132
discharge tube to a very low temperature. As before, he main-
tained the tube in connection with the air pump so as to be able
to vary the vacuum. The reduction of temperature was obtained
by means of ice water. Of course the bulb could not be placed
in the water itself on account of troubfe which would occur from
electrolysis, therefore, the discharge tube was immersed in a
vessel of oil, 13, which in turn was surrounded by a freezing
mixture. The vessel was a stout battery jar 14 inches high,
eight inches in diameter with glass walls Y 5 ^ of an inch thick.
The oil employed was paraffine. The refrigerating jar was 12
inches high and 12 inches in diameter and the glass wall thereof,
J4 inch thick. He tested the difference in the power of the rays
by first noticing the thickness of steel that was not penetrated
by the rays generated from the tube while in air. Crucible steel
ytg- of an inch thick did not transmit rays sufficiently to illuminate
the sciascope, and yet with the use of oil and reduction of tem-
perature, and after the rays had passed through two thicknesses
of glass as well as through the oil and ice water, the sciascope
was made luminous by rays after passing through a plate of
steel of double the thickness, i. e. y% in. thick. See in this con-
nection, Tesla's experiment, 135, where powerful rays were
obtained by immersing the discharge tube in oil. Accounts of
these two experiments were published simultaneously. Tesla
attributed the idea of this use of oil to Prof. Trowbridge of
Harvard University, who showed that a discharge tube immersed
in oil is adapted to the generation of X-rays of increased pene-
trating power. See cut at p. 135.
NON-REFLECTION OF X-RAYS. (Elect. Eng., Feb. 19, '96, p. 190.
Apparently extracted from the daily press.) That the X-rays
were only slightly reflected (Roentgen, 81), and even when
very powerful (Tesla, 146), was determined in a ^evere manner
by Edison. The first experiment consisted in employing a hm-
tiel 8 inches long and ^ inch at the smaller end. The dis-
charge tube was in the larger end, and the photographic plate
across the smaller end. After experiment and development,
the plate showed overlapping circular images, which would in-
dicate reflection from the inner surface of the funnel. This
may have been due to a jarring vibration of the funnel. There-
fore, he carried the experiment further by using a funnel 9 feet
long. The plate did not indicate any signs of reflection, as it
merely became generally fogged. The material of the tube is
not named, but if of brass or other impermeable metal, it is
thought that his experiment would have shown a result agree-
ing with that of others herein. Again, the reporter may have
t- HHHffl ..t
SCIAGRAPH OF RATTLESNAKE BY USE OF STOPS. loya, p. TOT.
By Leeds and Stokes.
134
been in error. Also, the rays may have been very weak, as the
experiment was performed when Edison first started to investi-
gate the subject.
136. X-RAYS NOT YET OBTAINABLE FROM OTHER SOURCES THAN
DISCHARGE TUBES. Edison exposed covered plates to the direct
sun-light at noon for three or four hours ; no photographic im-
pression ; also to electric sparks in open air, of twelve or more
inches in length ; no clouding even of the photographic plate.
Profs. Rowland et. al., of the Johns Hopkins University, in a
contribution to Electricity -, Apr. 22, '96, p. 219, confirmed this
point by stating : " As to other sources of Roentgen rays, we
have tried a torrent of electric sparks in air from a large bat-
tery, and have obtained none. Of course, coins laid on or near
the plate, under these circumstances, produce impressions, but
these are, of course, induction phenomena." (See Sandford and
McKay's Fig. p. 20). "As to sun-light, Tyndall, Abney, Graham,
Bell and others have shown that some of the rays penetrate
vulcanite and other opaque objects." Poincare, at an early date,
advanced the hypothesis that X-rays are due to phosphor-
escence, whether produced by electrical or other means. Elect.
World, Digest., Mar. 28, '96, p. 343, where it is also stated that
Chas. Henry thought a certain experiment of his own was in
favor of the hypothesis. The experiment was performed with
a phosphorescent material which had been exposed to the light
and then brought into darkness. Niewengloswski inferred, from
an experiment, that phosphorescent bodies increase the penetrat-
ing power of sun-light. Tesla admitted the possibility of the
radiation of X-rays from the sun. In an article describing im-
portant experiments in the Elect. Rev., N. Y., Apr. 22, '96, p.
207, he stated: "I infer, therefore, that the sun-light and
other sources of radiant energy must, in a less degree, emit
radiations or streamers of matter similar to those thrown off by
an electrode in a highly exhausted enclosure. This seems to be
at this moment still a matter of controversy." Roentgen, in
his first announcement, showed that the phosphorescent spot was
the source of the X-rays. 79 and 80. All the different opin-
ions and theories, therefore, indicated that phosphorescence by
sun-light might possibly emit X-rays. Probably few had suffi-
cient belief in the matter, one way or the other, to try the ex-
periment in an extreme manner. The author was curious to
prove the question, but he only obtained negative results. It
cannot be conceived how the matter could have been more se-
verely tested, for he concentrated the light of the sun nearly to
a focus by a large lens, namely 5 in. in diameter, together with
a reflecting funnel. The maximum phosphorescence was there-
fore obtained by placing suitable chemicals at the opening in
the funnel. The sciascope showed absolutely no X-rays present.
Photographic plates were not in the least ^acted upon, even after
COOLING DISCHARGE TUBE. EDISON. 135.
hours of exposure, the same having opaque covers of alumi-
num. See Elect. Eng., N. Y., Apr. 8, '96, p. 356. If X-rays are
emitted from the sun, they are all absorbed by the atmosphere
of the earth, or are overcome by some other force.
CHAPTER XI.
137. TESLA'S EXPERIMENTS. Elec. Rev., N. Y., March n, '965,
page 131, March 18, page 147, April i, page 171, and April 8,
page 183. KIND OF ELECTRICAL APPARATUS FOR OPERATING-
DISCHARGE TUBES FOR POWERFUL X-RAYS. ic6, 109, 114, 131.
The experiments performed by Nikola Tesla were particularly
noteworthy for the magnitude and intensity of the rays gener-
ated by his apparatus, under his skilful manipulation of the
adjustments and circuits particularly as to resonance. The re-
markable results that he obtained are not surprising when we
learn that he employed his well known system for producing
exceedingly enormous potential and unusually high frequency.
51. The primary electrical generator as he indicated and as
apparent from his system referred to in the above section, could
be either a direct or alternating current generator, or other
form. If the first is employed, of course an interrupter is neces-
sary in order that there may be a current induced in the
secondary.
Mr. Oliver B. Shallenberger, (Mem. Amer. Inst. Elec. Eng.)
whose laboratory is in Rochester, Pa., gave some important gen-
eral instructions concerning the Tesla system 51, that he
employed in the production of remarkably clear sciagraphs, in
conjunction with the focus tube, 91. representing the hand at
page 68, and showing a rat shown at this 137. (Elec. World,)
N. Y., March 17, '96.) Even the ligaments were clearly shown
in the sciagraph of the rat, and some of them are dimly repro-
duced by the half tone process. As to the apparatus and opera-
tion, which are especially important, it may be stated that the
current was taken from an alternator, of a frequency of 133
periods per second, and passed through a primary coil of a trans-
former for increasing the E. M. F. from 100 volts to from 16 to
25 thousand. The secondary current was then passed through
Leyden jars and a double cascade of slightly separated brass
cylinders, whereby it was changed into an oscillatory current of
an extremely high frequency, which was then conducted through
the primary of a second induction coil having very few turns of
136
SCIAGRAPH OF RAT, TAKEN BY OLIVER B. SHALLENBERGER WITH FOCUS-TUBE
(CUT AT p. 81) AND TESLA SYSTEM. 137, pp. 136 and 138.
'38
wire, and no iron core and having a ratio of 7 to i. By this
means the E. M. F. was raised to somewhere between 160,000
volts to 250,000, and was used to energize the discharge tube for
the generation of X-rays. Caution should be taken, because the
current coming from the first transformer, being of large quan-
tity and very high E. M. F. is exceedingly dangerous, but the
current of the second secondary has been passed through one's
body without danger, as reported by Mr. Tesla several years
ago, and confirmed by Mr. Shallenberger.
138. PHOSPHORESCENT SPOT MAINTAINED COOL. In testing the
power of the X-rays in connection with the appearance of the
phosphorescent spot, Tesla noticed that they were most power-
ful when the cathode rays caused the glass to appear as if it
were in a fluid state. 61. To prevent actual puncture, he
maintained the spot cool by means of jets of cold air. It be-
came possible thereby to use bulbs of thin glass at the location
of the generation of the X-rays. 119. He concluded from
certain results that not only was glass a better material for
discharge tubes than aluminum, but because, by other tests, he
found that thin aluminum cast more shadow with X-rays than
thicker glass. There are, of course, many other reasons, based
on mechanical construction, why glass is preferable, and also
why a tube with an aluminum window is not to be desired.
Principally, the latter will soon leak.
139. EXPULSION OF MATERIAL PARTICLES THROUGH THE
WALLS OF A DISCHARGE TUBE. At quite a low vacuum, and
after sealing off the lamp, he attached its terminal to that of
the disruptive coil. After a wnile, the vacuum became enor-
mously higher, as indicated by the following steps : First, a tur-
bid and whitish, light existed throughout the bulb. This was
the first principal characteristic. Next, the color changed to
red, and the electrode became very hot, in that case where pow-
erful apparatus was employed. The precaution should be taken
to regulate the E. M. F., to prevent destruction of the electrode.
Gradually, the reddish light subsided, and white cathode rays,
which had begun, grew dimmer and dimmer until invisible. At
the same time, the phosphorescent spot became brighter and
brighter and hotter and hotter, while the electrode cooled, until
the glass adjacent thereto was uncomfortably cold to the touch.
At this stage, the required degree of exhaustion was reached,
and yet without any kind of a pump. He was enabled to has-
ten the process by alternate heating and cooling, and by the
use of a small electrode. This whole phenomenon was exhi-
bited with external electrodes as well. He acknowledged that
instead of the disruptive coil, a static machine could be used,
or, in fact, any generator or combination of devices adapted to
produce a very high E. M. F.
The reduction of temperature of the electrode he attributed
to its volatilization. Without actually testing the rays with a
fluorescent screen or photographic plate, he could always know
their presence by the relative temperatures of the phosphor-
escent spot and the electrode, for when the latter was at a low
temperature and the former at a high temperature, X-rays were
sure to be strong.
From the fact that the vacuum became higher and higher by
the means stated, he was very much inclined to believe that
there was an expulsion of material particles through the walls of
the bulb. When these particles which were passing with very
great velocities struck the sensitive photographic plate they
should produce chemical action. He referred to the great velo-
city of projected particles within a discharge tube, pages 46 and
47, and to Lord Kelvin's estimate upon the same, and reasoned
that with very high potentials, the speed might be 100 km per
second. The phenomenon indicated, he said, that the particles
were projected through the wall of the tube and he entered into
an elaborate discussion on this point. He referred to his own
experiment of causing the rays from an electrode in the open
air to pass directly through a thick glass plate. 13. He performed
an experiment also of producing a blackening upon a photo-
graphic plate apparently by the projected particles, an electrical
screen being employed to prevent the formation of sparks. 35.
which as well known will cause chemical action upon the plate.
No stronger proof as to the expulsion of material particles could
be desired than an operation in which the eyes can see for
themselves that such an action must have taken place. Usually
he was troubled by the streamers (cathode rays) from the elec-
trode suddenly breaking the glass of the discharge tube. This
occurred when the spot struck was at or near the point where the
same was sealed from the pump. He arranged a tube in which
the streamers did not strike the sealing point, but rather the side
of the tube. It was extraordinary that a visible but fine hole
was made through the wall of the tube, and especially that no
air rushed into the vacuum. On the other hand, the pressure
of the air was overcome by something rushing out of the tube
through the hole. The glass around the hole was not very hot,
although if care were not taken, it would become much hotter,
and soften and bulge out, also indicating a pressure within, 27,
greater than the atmospheric pressure. He maintained the
140
punctured tube in this condition for some time and the rare-
faction continued to increase. As to the appearances, the
streamers were not only visible within the tube, but could be
seen passing through the hole, but as the vacuum became higher
and higher, the streamers became less and less bright. At a
little higher degree of vacuum, the streamers were still visible
at the heated spot, but finally disappeared.
This electrical process of evacuating varies in its rapidity
according to the thinness of the glass. Here again he noted
the application of his theory in that an easier passage was af-
forded for the ions. 47. A few minutes of operation produced
through thin glass, a vacuum from very low to very high,
whereas, to obtain the same vacuum through much thicker glass
over y^ hour was necessary. Again with a thick electrode the
time required was much greater. The small hole was not
always visible and it was thought that the material went through
the pores. The result obtained by the following experiment
tends to uphold Mr. Tesla's emission theory.
1390. LAFAY'S EXPERIMENT. GIVING TO X-RAYS THE PROPERTY
OF BEING DEFLECTED BY A MAGNET BY PASSING THEM THROUGH
A CHARGED SILVER LEAF. Comptes Rendus, March 23, '96 and
April 7, 13, 27, and L'Ind. Elec., April and May '96. From
trans, by Louis M. Pignolet. He placed at about .5 cm. below
a discharge tube, a lead screen pierced by a slit 2 mm. wide ;
and 0.04 m. lower, a second lead screen having a slit 5 mm. wide
completely covered by an extremely thin leaf of silver. Opposite
the silver leaf and exactly in the axis of the slit, was fixed a
platinum wire 1.5 mm. diameter. Thus, the rays which passed
successively through the two slits projected a shadow of the
wire on a photographic plate below.
When the silver leaf was connected to the negative pole of
the induction coil that excited the tube, the rays, which had be-
come electrified ( 6i3, p. 47) bypassing through the leaf, were
deflected by a magnetic field of about 400 L. G. s. units, whose
lines of force were parallel to the slit. The direction of the de-
flection was determined by the same law as that of the deflec-
tion by a magnetic field of the cathode rays in the interior of a
discharge tube. 59. When the silver leaf was not connected
to the coil, no deflection was produced. 79.
To double the apparent deflection, one part of the slit was
covered by a lead plate during the first half of the experiment.
The lead plate was removed and placed over the other part of
the slit, and the direction of the magnetic field reversed daring
the last half of the experiment. Thus the distance on the-
sciagraph between the two parts of the wire, was double the de-
flection produced by the magnetic field.
The deflection was in the same direction when the silver leaf
was connected to the negative pole of a static electric machine,
but was in the opposite direction when the leaf was connected to
the positive pole of the machine. The test was criticised in
the scientific press, and, therefore, in order to be certain that
the deflections observed were not due to the combined effects of
the electro-magnet which produced the magnetic field and the
electric field of the charged silver leaf, the experiments were
modified. To remove this uncertainty, the electrified rays were
caused to enter a grounded Faraday cylinder (see figure at
E. F. G. H., p. 48), through a small opening, before passing
between the poles of, -the electro-magnet. The deviations
which were recorded on a photographic plate in the box were
the same as before.
Additonal experiments showed that the deflections by the
magnetic field took place as well when the rays were electrified,
after their passage through another magnetic field, as before.
Lafay continued the experiments in great detail and by
many control tests, and he took accurate measurements and
followed the suggestions of others. It would be well for those
who have facilities to repeat these most interesting and import-
ant researches, to determine for themselves some satisfaction.
It is of interest to note that an American, Paul A. N. Winand,
(Mem. Arner. Inst. Elect. Engs.), in the absence of facilities for
experimenting, proposed (Elect. World, N. Y., Jnne 6, '96) to
interpose a hollow sphere, which had high potential, in the path
of X-rays, and to learn in what manner, if any, the rays are in-
fluenced. He argued that it would seem natural that, inasmuch
as the rays produce a discharge, there should be a reaction of
the charged surface upon the rays.
It is evident that if any one repeats these experiments, ex-
pert manipulation is required.
139^. GOUY'S EXPERIMENTS. THE PENETRATION OF GASES
INTO THE GLASS WALLS OF DISCHARGE TUBES. Comptes Rendus.
March 30, '96. From trans, by Louis M. Pignolet. From ob-
servations with slightly different glass from four tubes, it seemed
that the cathode rays cause the gases in the tubes to penetrate
the glass where they remain occluded until the glass is nearly
softened (after cutting off the current), by heat, whereby they
are set at liberty as minute bubbles visible by the microscope,
which finally partly combine and become visible to the the naked
eye.
I FT. DIAM., IN CLEAR AIR, AROUND INCANDESCENT ELECTRIC LAMPS
OF USUAL SIZE. CROSS AT CENTER OF EACH HALO. 140, p. 143.
Observed by means ol a photograph, in 1882, by William J Hammer.
MORTIFICATION OF THE ULNA. 204a.
From sciagraph by Prof Miller.
'43
Under the same conditions, tubes which have been used for
a long time exhibit numerous wrinkles, indicating a superficial
modification of the glass. These may exist with or without
the bubbles.
140. DISCHARGE TUBE SURROUNDED BY A VIOLET HALO.
By means of enormous potential and high frequency, the tube
was surrounded, Tesla stated, by violet luminosity or halo. 65
and 74. From the fact that Lenard obtained a similar appear-
ance in front of the aluminum window, it might be reasonable
to conclude that there is some close relationship between the
two phenomena.
As an illustration of halo by light, may be mentioned the well
known appearance so often occurring in the atmosphere con-
centrically with the moon, and sometimes surrounding the sun.
Under favorable circumstances, (in a mist or dust in the air), a
halo, at some distance from a flame or other light is faintly
visible. It has generally been assumed that the reason of a halo
by light is based upon the laws of reflection, or refraction or
both, the bending of the rays taking place, through, or upon the
surface of the particles of moisture. Others have held that
particles of ice in the upper atmosphere, are the reflectors or
refractors, or both. More puzzling has been the attempt to ex-
plain the novel appearance re-produced fairly well in the cut,
page 140. It is here represented in print for the first time, but
the photograph from which it was taken, was at various times,
shown to different physicists, some of whom attributed the
beautiful effect to the property of interference of light, and
naming Newton's rings as an analagous production. Prof.
Anthony in an interview expressed himself as well satisfied
that interference could not occur under the circumstances named.
He recognized that there was a curved surface of glass which
might be considered as made up of an infinite number of layers.
The author introduces the matter for the purpose of consider-
ation by others, and especially because it is so intimately con-
nected with the subject of the vacuum tube and electricity.
The details must be understood for the purpose of proper ap-
preciation. Mr. William J. Hammer, of New York, had a.
photograph taken of the large Concert Hall at the Crystal
Palace, Sydenham, Eng., by the light of the Edison incandescent
lamps with which the Hall was illuminated. This photograph
was made in 1882 during the International Electrical Exhibition
held at the Crystal Palace. The picture shows a small section
of the whole photograph and represents (although probably no
one would judge so by looking at the picture) a festoon otpear-
M4
shaped incandescent electric lamps, each one hanging down-
ward, and separated from its neighbor by between three and four
feet. They were so far away from the camera that a picture of
the lamps tmlighted, would have represented them as mere
specks. The bright circles with the bright central crosses in
the centre of the dark spaces were, therefore, fully one foot in
diameter, while the lamp bulbs themselves were only about two
or three inches thick, as usual. Why then should there be the
halos ? Why should the crosses appear ? And why should the
black area be so large ? If the electricity and vacuum have
nothing to do with it, wh) 7 " should not the halos appear when
photographs are taken of flames and other sources of light in
the absence of mist and dust ? In order to answer questions
which will perhaps be proposed, let it be stated that there was no
visible dust nor moisture in the room, the photograph being
taken early in the evening and at a time when the Hall was not
in use. The halos were not apparent except when re-produced
by a photograph. The lamps had the usual carbon filaments
hanging so that the several filaments were in different planes,
and they were of 16 candle power and were connected in par-
allel circuit, the average E. M. F. being about no volts. The
lamps were fed by the Edison direct current dynamos. The
festoon shown, is one of a dozen or more which were suspended
between the columns rising from the gallery and supporting the
roof and were hung about forty feet from the floor. The hall
was further illuminated by a huge electrolier pendant from the
centre of the ceiling. These details were obtained from Mr.
Hammer, who planned the installation.
141. ANESTHETIC PROPERTIES OF X-RAYS. Tesla reported
that he and his assistants tested the action of the rays upon the
human system, and found that upon continued impact and pen-
etration of the head by very powerful radiations, strange
effects were noticed. He was sure that from this cause a ten-
dency to sleep occurred ( 84, at end), and the faculties were be-
numbed. He said that time seemed to pass quickly. The
general effect was of a soothing nature, and the top of the head
seemed to feel warm under the influence of the rays. Inci-
dentally, he noticed, as he stated, " When working with highly
strained bulbs, I frequently experienced a sudden and some-
times even painful shock in the eye. Such shocks may occur so
often that the eye gets inflamed, and one cannot be considered
cautious if he abstains from watching the bulb too closely."
The author calls to mind the reports in the daily press that
Edison also noticed that the eyes were in some way sensitive to
145
the rays. The eye, it was reported, became fatigued at the
time, and yet later, objects could be more easily distinguished.
In this connection, it should be remembered that there are
not only cathode rays, X-rays, etc., but the electric force that
Lenard spoke of in the neighborhood of the discharge tube,
.and in testing the effects upon the eyes, of course, the precau-
tion should be taken to determine whether cathode rays, X-rays
or the electric sparks are answerable for the peculiar effects.
Roentgen reasoned, 84, that the eyes were not sensitive, but
the rays, in his case, were not strong enough to travel 40 to
60 feet, as in Tesla's experiments, but only 2 m. (about 7 ft.).
142. SCIAGRAPHS OF HAIR, FUR, HEART, ETC., BY X-RAYS.
Tesla was probably the first to be at all successful in the repre-
sentation in sciagraphs of such objects as hair and cloth and
similar easily permeable objects. In the case of a rabbit, not
only was the skeleton visible, but also the fur. Sciagraphs of
birds exhibited the feathers fairly distinctly. The picture of a
foot in a shoe not only represented the bones of the foot, and
nails of the shoe, but every fold of the leather, trowsers, stock-
ings, etc. His opinion as to the useful application of the rays
was that any metal object, or bony or chalky deposit could be
-" infallibly detected in any part of the body." In obtaining a
sciagraph of a skull, vertebral column, and arm, even the
shadows of the hair were clearly apparent. It was during such
an experiment that the anaesthetic qualities were noticed. The
author saw several of the above named sciagraphs. Further-
more, on the screen he believed he detected the pulsations of
the heart. Elect. Rev., N. Y., May, 20, '96.
Although we do not doubt this report concerning what Mr.
Tesla saw, yet some scientific men are exceedingly dubious
concerning the results obtained by other scientists, unless the
.same are confirmed by additional witnesses. It will certainly
be of interest to such skeptics to have corroboratory evidence.
In company with Prof. Anthony, Mr. Wm. J. Hammer and Mr.
Price, editor of the Elect. Rev., N. Y., the author visited a labo-
ratory at 31 West 55th street, New York City, for the purpose of
beholding the pulsations of the human heart by means of an
experiment performed by Mr. H. D. Hawkes, of Tarry town,
N. Y. There was nothing new about his apparatus, the admi-
rable results being due merely to accurately proportioned elec-
trical and mechanical details and skillful manipulation. The
Tesla system was not used, but merely a large induction coil and
rotary interrupter, and a direct current from the incandescent
lamp circuit of no volts, all substantially as Roentgen himself
146
employed. The sciascope was provided with the Edison calcic-
tungstate screen. In order to overcome the sparking between
the terminals on the outside of the tube after a few minutes of
use, he heated the cathode end by means of a Bunsen burner
flame. 139, near beginning. The utility consisted in the
evaporation of condensed moisture upon the cool end of the
discharge tube. The temporary heating always prevented, for
several minutes, any sparking on the outside. After some
preliminary experiments, each person, in turn, pressed the scia-
scope upon the breast of another, at the location of the heart,
while the discharge tube was directly at the back of a young
man. The ribs and spinal column were visible, and, projecting
from the spine, appeared a semi-circular area, which expanded
and contracted. Any one viewing such an operation, and know-
ing that he is looking at the movements of the heart, cannot
but be impressed with wierd wonder, and cannot but credit great
honor, not only to Roentgen and Lenard, but to all those early
workers who have gradually but surely, successfully made dis-
covery after discovery in the department of the science of dis-
charges, finally culminating in the most wonderful discovery
of all.
The author remembers seeing in some medical paper that
William J. Morton, M.D., of New York, had also witnessed the
beating of the heart with the sciascope at an early date. Simi-
lar reports are occurring weekly.
1420. Mr. Norton, of Boston (Elect. World., N. Y., May 23,
'96) also stated that the heart could be seen in faint outline, and
also its pulsations. The lungs were very transparent. The
liver being quite opaque, its rise and fall with the diaphragm
was plainly followed. Others have suggested drinking an
opaque (to X-rays) liquid, like salt water, and tracing its path.
143. PROPAGATION OF X-RAYS THROUGH AIR TO DISTANCES or
60 FT. In Roentgen's first experiments, the maximum dis-
tances at which the fluorescent screen was excited was about
7 ft. Tesla obtained similar action at a distance of over 40 ft.
Photographic plates were found clouded if left at a distance of
60 ft. for any length of time. This trouble occurred when some
plates were in the floor above and 60 ft. distant from the dis-
charge tube. He attributed the wonderful increase largely to
the employment of a single electrode discharge tube, because
the same permitted the highest obtainable E. M. F. that could be
desired.
144. X-RAYS WITH POOR VACUUM AND HlGH POTENTIAL.
In the course of Tesla's experiments, he observed that the
SCIAGRAPH OF FOOT IN LACE SHOE. 204.
By Prof. Miller.
148
Crookes' phenomena and X-rays could be produced without the
high degree of vacuum usually considered necessary, 118,
but by way of compensation, the E. M. F. must be exceedingly
high, and, of course, the tube and electrical apparatus substan-
tially of those dimensions involved in Tesla's work. One
must be careful not to over-heat the discharge tube, which is
likely to occur by increase of potential. He gave definite in-
structions for preventing the destruction of the tube by heating,
by stating that it is only necessary to reduce the number of im-
pulses, or to lengthen their duration, while at the same time
raising their potential. For this purpose, it is best to have a
rotary circuit interrupter in the primary instead of a vibrating
make and break, for then it becomes convenient to vary the
speed of the interrupter, which may be, evidently, so con-
structed that the duration of the impulses may also be varied,
for example, by different sets of contact points arranged on the
rotary interrupter, and made of different widths.
145. DETAIL CONSTRUCTION AND USE OF SINGLE ELECTRODE
DISCHARGE TUBES FOR X-RAYS. He pointed out that with two
electrodes in a bulb as previously employed by nearly all ex-
perimenters, or an internal one in combination with an adjacent
external one the E. M. F. applicable was necessarily greatly limited
for the reason that the presence of both, or the nearness of any
conducting object "had the effect of producing the practicable
potential on the cathode." Consequently he was driven, as he
said, to a discharge tube having a single internal electrode, the
other one being as far away as required. 9. In view of his
ingenious arrangements of the disruptive coil, and circuits, con-
densers and static screens for the bulb, he found it immaterial
to pay attention to some other details followed by experimen-
ters. For example, it made comparatively little difference in
his results whether the electrode was a flat disk or had a concave
surface.
The form of tube described by Tesla in full, will hereinafter
be alluded to as exhibited in the several figures accompanying
this description, and it consisted, therefore, of the long tube ""
made of very thick glass except at the end opposite the electrode
V, where it was blown thin, p. 149. The electrode was an alumi-
num disk having a diameter only slightly less than that of the
tube and located about one inch beyond the rather long narrow
neck n, into which the leading-in wire c entered. It is important
that a wrapping w be provided around this wire, both inside and
outside of the tube. The sealing point was on the side of the
neck. An electric screen has been referred to heretofore. It is
149
lettered s, and was formed of a coating of bronze paint applied
on the glass between the electrode and neck n. The screen
could be made in other ways, for example, as shown at s, Fig. 2,
where it consists of an annular disk behind and parallel to the
electrode disk. This ring s in Fig. 2 must be placed at the right
distance back of the electrode e, but just how far can only be
determined by experience. The uniqne service of the screen
was that of an automatic system for preventing the vacuum
from becoming too high by use. The peculiar action was as
TESLA'S FIGS, i AND 2, REFLECTION AND TRANSMISSION OF X-RAYS
BY DIFFERENT SUBSTANCES. 145 and 1460.
follows, namely from time to time, a spark jumped through the
wrapping w within the tube to the screen and liberated just
about enough gas to maintain the vacuum at an approximately
constant degree. Another way in which he was able to guard
against too high a vacuum, consisted in extending the wrapping
w to such a distance inside of the tube, that the same became
heated sufficiently to liberate occluded gases. As to the long
length of the leading-in wire within a long neck behind the
cathode, Lenard found the same to be valuable in conjunction
with a wrapping around the wire. With high potential, a spark,
at a certain high degree of vacuum, formed behind the electrode,
and prevented the use of very high potential, but by having the
wire extend far into the tube and providing wrappers, the spark-
ing was much less likely to occur. By proper adjustment as
before intimated, Tesla could produce just about enough to
compensate for the electrical increase of the vacuum. Another
difficulty that presented itself in connection with high E. M. F.
was the undue formation of streamers heretofore referred to,
apparently issuing from the glass, and so often disabling it. He
therefore immersed the discharge tube in oil as pointed out in
detail hereinafter. The walls of the tube served to throw for-
ward to the thin glass many of those rays that otherwise would
have been scattered laterally. Upon comparing a long thick
tube of this kind with a spherical one, the sensitive plate was
acted upon by the rays in % the time with the tube. A modi-
fication consisted in surrounding a lower portion of the tube,
with an outside terminal e, indicated in dotted lines in Fig. i.
In this way the discharge tube had two terminals. The great-
est advantage probably in using a long tube, was that the longer
it was, within the proper limits, the greater the potential which
could be applied with advantages. As to the aluminum elec-
trode, he noticed that it was superior, in comparison with one
made of platinum which gave inferior results, and caused the bulb
to become disabled in an inconveniently short period of time.
146. PERCENTAGE OF REFLECTED X-RAYS. He performed some
preliminary experiments, testing roughly as to whether any ap-
preciable amount of radiation could be reflected or not from
any given surface. Within 45 minutes he was enabled to obtain
clear and sharp sciagraphs of metal objects, and the same could
have been obtained only by the reflected rays, because he
screened the direct rays by means of very thick copper. By a
rough calculation he found that the percentage of the total
amount of rays reflected was somewhere in the neighborhood of
2 per cent.
Prof. Rood, of Columbia University, N. Y., (Sci. Mar. 27, '96.)
by means of an experiment with platinum foil, 80, concluded
that the per centage was about .005, the incident angle being
45 degrees. He regarded this figure as the mere first approxi-
mation. Judging from Roentgen, 85, Tesla, Rood and others,
therefore, it seems to be established that the percentage of
X-rays reflected is very small.
Prof. Mayer, of Stevens Institute, (Science, May 8, '96,) is of
151
the opinion that there is a regular or specular reflection, having
witnessed some experiments obtained by Prof. Rood, of Colum-
bia Univ., N. Y. Prof. Mayer reported that the original nega-
tives were taken in such a way as to substantiate regular
reflection, and were carefully examined by six eminent phy-
sicists at the National Acad. of Set. at Washington, April 23, '96,
and none had the slightest doubt concerning the completeness
of the demonstration. The material employed for reflecting
was platinum foil. 1030.
DIFFERENCE BETWEEN DIFFUSION AND REFLECTION. Judging
from the experiments above related, as well as those considered
in 1030, there might at first appear to be contradictory results,
reported by different authorities. Experts, it is thought will,
without argument, discover the harmonious agreement, and will
commend the work of scientists, who, in different parts of the
world, and at about the same time, made similar experiments,
which now being considered jointly, are found to agree so won-
derfully closely. Upon reading the above sections and those
referred to, there can be no doubt whatever but that X-rays,
upon striking a body are, to a certain per cent, scattered, or
thrown back, or bent from their straight course, and sent in a
"backward and different direction, at one angle or another. The
only apparent absolute contradiction to this is that of Perrin,
1 030, near the end. But his is a case of one witness against
scores, and, therefore, evidence based upon his experiments,
must be counted out. The error was either due to some over-
sight of his own, or more probably the mistake is merely a
typographical one, for often a mistake creeps in between a man's
dictation and the printed work. It is difficult to accuse Perrin
of a mistake, for he is a great French authority in such matters.
Assuming that no error has occured, let it be noticed that he does
not pronounce non-reflection from all substances, but only from
steel p. 154, 1. 9, and flint, which have been so polished as to form
a mirror-like surface, whereas all other experimenters, with
scarcely an exception, have not employed such surfaces. The
difficult point to believe is that, after six hours, no energy from
the mirror could be collected. If we accept Perrin's results it
must be only in regard to those two particular materials, pol-
ished steel and flint. Another feature which is on the edge of
conjecture, is that of true or specular reflection, referred to by
Prof. Mayer, 146. Many attempts have been undertaken to
prove whether the rays were thrown backward on the principle
of reflection as light from a mirror, or of diffusion as light from
chalk. Let the student notice that the evidence is overwhelming
in favor of the turning back of the rays to a very small per cent,
upon striking any object. As to specular reflection, which means-
similar to the reflection of light from a polished mirror, it is
practically the same as diffusion, the difference being substantially
of a technical nature. This allegation is based upon the detail
distinction between reflection and diffusion given by P. G. Tait,
professor of natural philosophy, Univ. of Edinburgh, who states,
in Encyclo. Brit., vol. 141, p. 586:
"It is by scattered light that non-luminous objects are, in gen-
eral, made visible. Contrast, for instance, the effect when a ray
of sunlight in a dark room falls upon a piece of polished silver,
and when it falls on a piece of chalk. Unless there be dust
or scratches on the silver, you cannot see it, because no light
is given from it from surrounding bodies except in one definite
direction, into which (practically) the whole ray of sunlight is
diverted. But the chalk sends light to all surrounding bodies,
from which any part of its illuminated sides can be seen ; and
there is no special direction in which it sends a more powerful
ray than in others. It is probable that if we could, with suffi-
cient closeness, examine the surface of the chalk, we should
find its behavior to be in the nature of reflection, but reflection
due to little mirrors inclined to all conceivable aspects, and to all
conceivable angles to the incident light. Thus scattering may be
looked upon as ultimately due to reflection. When the sea is perfectly
calm, we see it in one intolerably bright image of the sun only.
But when it is continuously covered with slight ripples, the de-
finite image is broken up, and we have a large surface of the
water shining by what is virtually scattered light, though it is
really made up of parts each of which is as truly reflected as it
was when the surface was flat."
1460. REFLECTED AND TRANSMITTED X-RAYS COMPARED.
In order to carry on a series of investigations, Mr. Tesla con-
structed a complete special apparatus represented in Fig. 2, p.
149, and embodied in it also an idea which he attributed to Prof.
William A. Anthony, which consisted in arranging for scia-
graphs to be produced by the rays transmitted through the re-
flecting substance as well as by the reflected rays themselves.
The figure serves to show at a glance the construction and,
therefore, the explanation need be but brief. It consisted of a
T tube, having three openings, those at the base and side being
closed by photographic plates in their opaque holders, which car-
ried on the outside the objects o and o to be sciagraphed. At an
angle to both plates, and centrally located, was a reflecting
plate, r, which could be replaced by plates of different materi-
'53
als. At the upper opening of the plate B was a discharge tube,
b, placed in a heavy Bohemian glass tube, t, to direct the scat-
tered rays downward as much as possible from the electrode, e,
to and through the thin end of the discharge tube. The objects
to be sciagraphed, namely o and o ', were exact duplicates of
each other, No statement could be found as to the thickness of
the tested plates, r, except that they were all of equal size.
The distance from the bottom of the discharge tube to the re-
flecting plate, r y was 13 inches, and from the latter to each pho-
tographic plate about 7 inches, so that both pencils of rays had
to travel 20 inches in each instance. One hour was taken as
the time of exposure. After a series of experiments with a
great many different kinds of metals, they arranged themselves
as to their reflecting power, in an order corresponding to Volta's
electric contact series in air. 153. The most electro-positive
metal was the best reflector, and so on. For exhaustive in-
vestigations upon the discovery of Volta, see " Experimental Re-
searches" of Kohlrausch, Pogg. Ann., '53, and Gerland, Pogg. Ann.,
'68. The metals Tesla tested were zinc, lead, tin, copper and
silver, which were, in their order, less and less reflecting, and
the order is the same in the electro-positive series, zinc being the
most positive, and the others less and less so, in the order named.
For a complete list of the metals arranged by the Volta series,
see any standard electrical text-book. He could not notice
much difference between the reflecting powers of tin and
lead, but he attributed this to an error in the observation.
He tried other metals, but they were either alloys or impure.
Those named in the list above were the pure metals. How-
ever, he carried on experiments with sheets of many different
substances, and arrived at the following table, which shows par-
ticularly the relative transmitting and reflecting powers of the
various substances in the rough.
Reflect^ Body ^y, Impression^ Reflect
Brass Strong Fairly good
Tool steel Barely perceptible Very feeble
Zinc None Very strong
Aluminum Very strong None
Copper None Fairly strong but much less
than zinc
Lead None Very strong but a little weaker
than zinc
Silver Strong, a thin plate Weaker than copper
being used
Tin None Very strong about like lead
Nickel None About like copper
Lead -glass Very strong Feeble
Mica Very strong Very strcng about like lead
Ebonite Strong About like copper.
154
By comparing, as in previous experiments, the intensity of
the photographic impression by reflected rays with an equivalent
impression due to a direct exposure of the same bulb and at the
same distance, that is, by calculations from the times of exposure
under assumption that the action upon the plate was proportion-
ate to the time, the following approximate results were obtained:
-r, a .. T> j Impression by Impression by
Reflecting Body ^^ JJJjJ Reflected Rays.
Brass ico 2
Tool steel 100 0.5
Zinc 100 3
Aluminum 100 o
Copper 100 2
Lead 100 2.5
Silver 100 1.75
Tin 100 2.5
Nickel 100 2
Lead-glass 100 i
Mica 100 2.5
Ebonite 100 2
He stated that while these figures can be but rough approxi-
mations, there is, nevertheless a fair probability that they are
correct, in so far as the relative values of the sciagraphic im-
pressions of the various objects by reflected rays are concerned.
In order to devise means for testing the comparative reflecting
power in a more decided manner, he laid pieces of different
metals side by side upon a lead plate. Consequently the reflect-
ing surface was formed of two parts corresponding to the two
metals. 80. The vertically perpendicular partition of lead
served to prevent the mingling of the rays from the two metals.
Ingenious precautions were taken; as for example, so arranging
matters that upon equal areas of the two plates, equal amounts
of X-rays impinged. 80. He undertook to determine the posi-
tion of iron in the series by thus comparing it with copper. It
was impossible to be sure which metal reflected better. The
same regarding tin and lead and also in reference to magnesium
and zinc. Here, a difference was noticed, namely that the mag-
nesium was a better reflector.
He has made practical application of the power of the sub-
stances to reflect a certain per cent, of the rays by employing
reflectors for the purpose of reducing the time required for ex-
posure of the photographic plates. It admits, he stated, of the
use of reflectors in combination with a whole set of discharge
tubes, whereby rays which would be otherwise scattered in all
directions are brought more nearly to a single direction of
propagation.
It might be argued, that in as much as zinc would reflect only
about three per cent, of the incident rays, no practical gain would
FROM SCIAGRAPH OF KNEE-JOINT. STRAIGHT, FRONT VIEW.
By Prof, Goodspeed. Photo. Times, July, '06.
156
ensue in sciagraphy by the use of a reflector. He pointed out
the falsity of such an argument. In the first place, the angle
employed in these tests was 45. With greater angles, the pro-
portion of reflected rays would be greater assuming that the law
of reflection is the same as that of light. By mathematical cal-
culation and tests, he showed that there was no doubt whatever
about the advantage of using reflectors. He obtained a scia-
graph, on a single plate, of the ribs, arms and shoulder, clearly
represented. He stated the details as follows. "A funnel
shaped zinc reflector two feet high, with an opening of five inches
at the bottom and 23 inches at the top, was used in the experi-
ment. A tube similar in every respect to those previously
described, was suspended in the funnel, so that only the static
screen of the tube was above the former. The exact distance
from the electrode to the sensitive plate was four and one- half
feet."
147. DISCHARGE TUBE PLACED IN OIL. When the E. M. F. was
increased, by having the discharge tube, as usual, in open air,
sparks formed behind the electrode, and within the vacuum,
and endangered the life of the discharge tube. He obviated
this difficulty partly by having the electrode located well within
the evacuated space, so that the wire leading to it was unusually
long. By excessive E. M. F., also, streamers broke out at the
end of the tube. To overcome all difficulties in connection
with sparking and breaking of the tube, he followed the propo-
sition of Prof. Trowbridge, and submerged the discharge tube
in oil, ii, at end, and 13, which was continually renewed by
flowing into and out of the vessel in which the discharge tube
was contained, all as shown in the accompanying figure, p. 157,
"Discharge Tube Immersed in Oil." The discharge tube,/,
may be recognized by its shape, and it is located horizontally
in a cylindrical tube lying sidewise upon a table. To regulate
the flow of the oil, the reservoir may be raised and lowered by
a bracket, s. The X-rays enter the outside atmosphere by
passing first through glass, then oil, and then through a dia-
phragm of " pergament " forming the right hand end of the
oil vessel. When the results were compared with those ob-
tained by Roentgen in his first experiments, the rays were
found so powerful that it is not surprising that Tesla was able
to obtain more definitely a closer knowledge of the properties
of the rays. Roentgen obtained, with his tube and a screen
of barium platino cyanide, a shadow picture of the bones of
the hand at a distance of less than 7 ft., while Tesla obtained
a similar picture with a screen of calcic tungstate, and with
liis tube immersed in oil at a distance of 45 ft. Tesla also made
sciagraphs with but a few minutes' exposure at a distance of
40 ft., by the help of Prof. Henry's method, i. e , with the as-
sistance of a fluorescent powder. 151. He referred also to Sal-
vioni's suggestion of a fluorescent emulsion. He attributed
to Mr. E. R. Hewitt the conjecture that the sharpness of the
sciagraphs might be increased by a thin aluminum sheet hav-
ing parallel groves. Several experiments were made, there-
fore, with wire gauze, as well as with a screen formed of a
mixture of fluorescent and iron-fluorescent powders. With the
strong power of the rays as obtained by Tesla in combination
with such adjuncts, the shadows were sharper, although the radi-
ation, of course, was weakened by the obstruction, g 107 b.
DISCHARGE TUBE IMMERSED IN OIL, 147, PAGE 156.
With the apparatus involving the discharge tube in oil, and
with tremendously high potential, he obtained what may be
called wonderful results ; for with the sciascope he obtained
shadow pictures of the vertebral column, outline of the hip bones,
the location of the heart (and later detected its pulsations), ribs
and shorter bones, and, without the least difficulty, the bones of
all the limbs. More than this, a sciagraph of the skeleton of the
hand was perceived through copper, iron or brass very nearly
^ inch thick, while glass YZ inch thick scarcely dimmed the flu-
orescence. The skull of the head of an assistant acted like-
wise, while at a distance of three feet from the discharge tube.
The motion of the hand was detected upon the screen although
'58
the rays first passed through one's body. In making observations
with the screen, he advised that experimenters should surround
the oil box closely, except at the end, with thick metal plates, to
prevent X-rays from coming in undesired directions by reflection
from different objects in the room. Obviously the shadows will
be sharper.
148. BODIES NOT MADE CONDUCTORS BY X-RAYS. Tesla re-
ferred to Prof. J. J. Thomson as having announced some time
ago " that all bodies traversed by Roentgen radiations become
conductors of electricity." The author has witnessed other simi-
lar expressions giving credit to Thomson in this respect, but he
understands that Prof. Thomson, having discovered that X-rays
discharge both negatively and positively charged bodies, con-
jectured or drew a corallary as to the probability of the bodies
therefore becoming conductors. Tesla, nevertheless, seems to
have proved that the corallary does not hold. In the first place
he employed the very powerful rays, and next, he let the oil be
the substance traversed by the rays. Besides this, he applied a
sensitive resonance test. See detail treatment of his experiments
on this subject in Elect. Rev., N. Y., June 24, '93, p. 228. In brief
"a secondary not in very close inductive relation to the primary
circuit, was connected to the latter and to the ground, and the
vibration through the primary was so adjusted that true reson-
ance took place. As the secondary had a considerable number
of turns, very small bodies attached to the free terminal produced
considerable variations of potential of the latter. Placing a tube
in a box of wood filled with oil and attaching it to the terminal,
I adjusted the vibration through the primary so that resonance
took place without the bulb radiating Roentgen rays to any ap-
preciable extent. I then changed the conditions so that the
bulb became very active in the production of the rays."
According to the corallary above referred to, the oil should be,
with such an environment and under such subjection, a con-
ductor of electricity, but it was not. He emphasized his satis-
faction in the results by saying " the method I followed is so
delicate that a mistake is almost an impossibility."
Prof. W. C. Peckham, Elect. World, N. Y., May 30, '96, reasoned
that the oscillating electro-static action upon the outside of the
tube, is concerned in the production of fluorescence, and other
properties of X-rays. ''These oscillations are certainly synchron-
ous with the vibrations of the cathode rays in the tube, which in
turn synchronize with the oscillation in the induction coil. If
the vibrations of the tube cannot keep time with those of its
coil, few or no X-rays will be given out. The cause seems to-
be similar to that of sympathetic vibrations in sound. In a word,
the discharge tube is a resonator for its coil, and when the coil
and tube are properly attuned, the maximum effect is obtained.
149. APPLEYARD'S EXPERIMENT. NON-CONDUCTORS MADE CON-
DUTORS BY CURRENT. Proc. Phil. So. y May n, Nature, Lon.,
May 24, '64, p. 93. A piece of celluloid was pressed between two
metal plates serving as terminals. A galvanometer was em-
ployed to indicate the diminution of resistance by time, and it
also showed that the electrification was negative. When mer-
cury was one of the metals, the abnormal resiilts did not occur,
except to a very small extent. When the celluloid was replaced
by gutta-percha tissue, the electrification was normal. Many
non-metals were employed, and several were lowered in resist-
ance.
1490. RESISTANCE SOMEWHAT INDEPENDENT OF METAL PAR-
TICLES. Through a mixture of conducting and non-conducting
materials, like a sheet of gutta percha, having brass filings im-
bedded therein, with 750 volts, no current passed, and this
held true until the proportion in weight of the metal to the
gutta percha was 2 to i. Let it be remembered, also, that se-
lenium is reduced as to resistance under the influence of light.
150. MINCHIN'S EXPERIMENT. RESISTANCE LOWERED BY ELEC-
TRO-MAGNETIC WAVES. Nature, Lon., May 24, '94, p. 93. Re-
ferring to Appleyard's experiment, it will be noticed that he
found that mixtures of certain limited per cents, of metal-
lic particles and insulators were exceedingly high in resist-
ance. Prof. G. M. Minchin found that such materials became
conductors under the influence of powerful electro-magnetic
disturbances, and that after the current was conducted, its
resistance remained greatly lowered in behalf of very weak
impulses, although, before the experiment, the resistance was so
high. 140. But after the current was interrupted by moving
the terminal away from the mixture, the high resisting power
returned slowly, at a rate somewhat in proportion to the hard-
ness of the mixture. The film employed consisted of shellac
or gelatine or sealing wax, while among the metals was pulver-
ized tin. In the latter case, the resistance was reduced by the
electro-magnetic waves from apparent infinity to 130 ohms, the
electrodes being displaced by i cm.
CHAPTER XII.
MISCELLANEOUS RESEARCHES ON ROENTGEN RAYS.
151. PUPIN AND SWINTON'S EXPERIMENT. SCIAGRAPHIC PLATES
COMBINED WITH FLUORESCENT SALTS. The Elect., Lon., Apr.
24f '96. Prof. Pupin, of Columbia College (Electricity, N. Y.,
Feb. J2, '96 the author saw him use it Feb. 7, '96 ), was
among the first, and probably actually the first, to lessen the
time of exposure by a fluorescent screen. Prof. Salvioni also
worked in this direction at an early date. Prof. Swinton re-
ported some details in the matter, and he was able to obtain a
sciagraph of the bones of the hand in less than 10 seconds,
with a moderately excited discharge tube, whereas, without the
screen the time was two minutes. He experimented first with
barium platino cyanide, but the results referred to were ob-
tained with calcic tungstate, finely ground, and made up into
paste by means of gum, and dried. He spread the same upon a
celluloid sheet which was placed with the celluloid side against
the photographic film. The difficulty experienced first was in
the formation of spots on the negative, because some of the
crystals fluoresced more than others. Such a defect, how-
ever, showed that the fluorescent salt increased the rapidity
of the action upon the photographic film. The result of this
experiment, as well as that of others, has sufficiently estab-
lished the fact that the fluorescent screen is of great importance
in connection with the art of rapid sciagraphy.
Phosphor sulphide of zinc is among those which hasten pho-
graphic action. (Chas. Henry, in Comptes Rendus, Feb. 10, '96.)
Dr. W. J. Morton employed the screen in taking the sciagraph
of the thorax, p. 61. The advantageous use is also confirmed by
BASILEWSKI (Comptes Rendus, March 23, '96. From trans, by
Louis M. Pignolet). The photographic plate was covered with
a sheet of paper coated with barium and platino-cyanide, so
that the two prepared surfaces were in contact, and the fluor-
escent paper was between the object and the plate.
J. W. Gifford, (Nature, May 21, '96) tried a great variety of
1 60
THORAX. 206.
By W. J. Morton, M.D. Fluorescent screen used ( 151).
- . i
NORMAL ELBOW. 204.
By Prof. Miller.
162
fluorescent bodies in combination with the photographic plate,,
and found that potassium platino cyanide was decidedly the best.
152. THOMPSON'S (S. P.) EXPERIMENT. PENETRATING POWER
OF X-RAYS VARIES WITH THE VACUUM. Comptes Rendus. CXIIL,
p. 809. The Elect., Lon., April 24, '96, p. 866. In a communi-
cation to the Academic des Science Prof. Sylvanus P. Thompson
of the University College of Liverpool, argued that by one kind
of X-rays the bones of the hand were more easily penetrated than
by another kind. The two varieties were produced by different
vacua. 75 and 76. Let the vacuum be supposed to become
higher and higher. At the first generation of the X-rays, the
fluorescent screen showed that the bones of the hand cast very
dark shadows. With increase of the vacuum, the shadows of
the bones were very faint. This result is also obtained by re-
duction of temperature. 1520.
1520. BLEEKRODE'S EXPERIMENT. PERMEABILITY AT Low TEM-
PERATURES INCREASED. Elect. Rev., Lon., June 12, '96. Experi-
ments performed by him confirmed those of Edison. 135.
An experiment by Prof. Dewar strongly confirmed the results.
They noticed the same peculiarity that Edison did, namely, that
the shadow of the finger exhibited the flesh and bones as if they
were equally transparent. Varied tests showed that the reduc-
tion of the temperature of glass increased its permeability.
153. MURRAY'S EXPERIMENT. REDUCTION OF THE CONTACT
POTENTIAL OF METALS BY X-RAYS. Trans. R. So., Mar. 19, '96.
The Elect., Lon., Apr. 24, '96, p. 857. J. R. E. Murray of the
Cavandish Laboratory, at the suggestion of Prof. J. J. Thomson,
carried on a long series of careful experiments, to find whether
the contact potential of a pair of plates of different metals was,
in any way, affected by the passage of X-rays between the plates.
All the ordinary precautions were taken. The contact potential
was measured by Thomson's (Kelvin) method, see Trans. Brit.
Asso., 1880. The important result obtained, was that "the air
through which the rays pass, 90, is temporarily converted into
an electrolyte, 47, and when in this condition forms a con-
nection between the plates, which has the same properties as a
drop of acidulated water, namely, it rapidly reduces the poten-
tial between the opposing surfaces of the plates to zero, and may
even reverse it to a small extent."
154. NODON'S EXPERIMENT. TRANSPARENCY OF DIFFERENTLY
COLORED MEDIA TO THE X-RAYS. Comptes Rendus, Feb. 3, '96.
From trans, by Louis M. Pignolet. The rays were passed
through two openings in a thick metal diaphragm, one of which
was covered by an uncolored piece of gelatine and the other by
i6 3
a piece ; tinted with the color to be tested. The two images were
received on the same plate. The various colors tested were
traversed with equal facility by the rays, 68 and 82.
The investigation described above was made by Albert Nodon
at the Laboratoire des Recherches Physiques a la Sorboune.
This agrees with Bleunard who found that colors seemed to
have no influence on the passage of the rays as water colored
with various analine colors offered no more resistance than
when pure. From trans, by L. M. P. Comptes Rendus, March, '96.
A. and L. Lumiere (Comptes Rendus, Feb. 17, '96,) observed
that the X-rays act in the same manner upon colored photo-
graphic plates rendered sensitive to various regions of the spec-
trum. Thus, plates sensitive to red, yellow and green gave
exactly the same impression, provided they had the same general
sensibility to white light. While this may not be accurately so,
it illustrates that materials are penetrated by X-rays indepen-
dently of the laws of color.
155. MESLANS. CHLORINE, IODINE, SULPHUR, PHOSPHORUS, COM-
BINED WITH CERTAIN COMPOUNDS, INCREASE OPACITY TO THE
X-RAYS (Comptes Rendus, Feb. 10, '96. From trans, by Louis M.
Pignolet.) Carbon in its various forms was found to be very trans-
parent, also organic substances containing, besides carbon, only
the gaseous elements hydrogen, oxygen and nitrogen; but this
transparency was far from uniform. Organic substances,
ethers, acids, nitrogenized compounds (corps azotes], were
easily traversed by the rays ; but the introduction of an inor-
ganic element, as particularly, chlorine, sulphur, phosphorus, and,
above all, iodine, renders them opaque. 82. This occurs also
with sulphates of the alkaloids. lodoform, the alkaloids, pieric
acid, fuchsine and urea are very transparent. Metallic salts are
very opaque, but this varies with the metal and the acid.
Bleunard went further into details. The opacity of solutions of
salts increased with the atomic weight of the metal and of the
metalloid. Water was easily traversed by the rays. Solutions
of bromide of potassium, chloride of antimony, bichromate of
potash offered considerable opposition to the passage of the
rays. Solutions of borate of soda, permangate of potassium
were easily traversed. The liquids were held in paper boxes.
The experiments above related were conducted by Maurice
Meslans at 1'Ecole de Pharmacie de Nancy.
156. BUQUET & GASCARD'S EXPERIMENTS. ACTION OF THE X-
RAYS UPON THE DIAMOND AND ITS IMITATIONS ; ALSO UPON JET.
Comptes Rendus, Feb. 24, 96. From trans, by Louis M. Pigno-
let. Sciagraphs taken by the X-rays showed that diamonds be-
FROM SCIAGRAPH OF PENCIL, KEY, FOUNTAIN-PEN, AND COIN. 1-61.
By Prof. McKay, Packer Institute.
FROM SCIAGRAPH BY PROF. MILLER. 156.
i. Real diamond. 2. Paste. 3. Glass. 4. Real diamond mounted in gold ring.
came transparent, and their shadows disappeared with long
exposures; but imitation diamonds remained opaque under the
same conditions. Jet was distinguished from its imitations by
the same method. The diamond and jet cast clearer shadows
on a fluorescent screen than their imitations.
The above tests were made by Albert Buquet and Albert Gas-
card, at the Cabinet de Physique de 1'Ecole des Sciences de
Rouen.
The half-tone on lower half of adjacent page, 164, was taken
from a sciagraph by Prof. Dayton C. Miller, of Case School of
Applied Science. The differences of opacity are proved, because
all were of same thickness and exposed simultaneously.
Prof. Sylvanus P. Thompson (The Elect., Lon., May 18 '96)
confirmed the above, and also found that, although the diamond
is more transparent than glass, it is more opaque than block
carbon or graphite.
Mineralogists are thus enabled to submit minerals to the
X-ray test in making analyses.
157. DUFOUR'S EXPERIMENT. INACTIVE DISCHARGE TUBES
MADE LUMINOUS BY X-RAYS. Comptes Rendus, Feb. 24, '96.
From trans, by Mr. Pignolet. He observed that very small and
sensitive Geissler tubes phosphoresced when exposed to X-rays.
22, 23.
158. BEAULARD'S EXPERIMENTS. NON-REFRACTION OF X-RAYS
IN A VACUUM. Comptes Rendus, Mar. 30, '96. From trans, by
Louis M. Pignolet. With prisms of ebonite, F. Beaulard held
that no decided deviation could be observed within the vacuum.
159. CARPENTIER'S EXPERIMENT. SCIAGRAPH SHOWING THE
PARTS IN RELIEF ON A COIN. Comptes Rendus, Mar. 2, '96. From
trans, by Louis M. Pignolet. An imprint of a coin stamped
upon a thin piece of well annealed aluminum by pressing the
coin against the aluminum, was reproduced in a sciagraph. The
raised parts of the coin were scarcely yl^ of a millimeter high.
The aluminum was -fa millimeter thick. This result is ad-
mirably represented by the sciagraph of an aluminum medal on
page 1 66, taken by Prof. Dayton C. Miller, of Case School of Ap-
plied Science, Elect. World, N. Y., Mar. 21, '96, who also made a
sciagraph of a copper plate % inch thick having blow holes
which appeared in the picture, but they could not be detected
by light, serving to illustrate an application of the new discovery
in testing the homogeneity of metals.
160. WUILLOMENET'S EXPERIMENTS. TRANSPARENCY OF THE
EYE TO THE X-RAYS DETERMINED BY SCIAGRAPH OF BULLET
THEREIN. Comptes Rendus, Mar. 23, '96. A sciagraph taken with
i66
an exposure of three hours showed perfectly a lead shot intro-
duced into the vitreous media of the eye of a full grown rabbit.
Therefore the opacity of the media of the eye was not absolute.
In a second series of experiments by Dr. Wuillomenet a
human head was used, but the results were negative in spite of
a great intensity of the rays and a long exposure, 82.
161. FERNAND RANWEZ'S EXPERIMENTS. APPLICATION OF THE
X-RAYS TO ANALYSIS OF VEGETABLE MATTER. Comptes * Rendus,
Apr. 13, '96. From trans, by Louis M. Pignolet. Sciagraphy
can render valuable services in analytical researches and
specially in the analysis of vegetable foods where they will show
the most usual adulterations consisting of mineral substances.
BAS-RELIEF SCIAGRAPH, 159, BY PROF. DAYTON C. MILLER.
This method offers several advantages for small samples of
the substances can be examined. The samples are not chemi-
cally changed. A great number of tests can be made in a short
time. Lastly, the sciagraph obtained affords a permanent
record.
The tests were made on samples of adulterated saffron com-
posed of mixtures of pure saffron and saffron coated with sul-
phate of barium. A sciagraph taken with an exposure of three
minutes showed scarcely visible imprints of the pure but strong
impressions of the adulterated. See sciagraph of pen, (min-
eral) in holder, (vegetable), in cut at upper part of p. 164, which
also shows the graphite in a wooden pencil.
i6 7
162. ERRERA'S EXPERIMENT. ACTION OF THE X-RAYS ON
PHYCOMYCES. HERTZ WAVES AND ROENTGEN RAYS NOT IDEN-
TICAL. Comptes Rendus, March 30, '96. From trans, by Louis
M. Pignolet. Phycomyces Nitens, when submitted to the assy-
metrical action of Hertz electric waves, became curved, accord-
ing to Hegler. Errera found a Phycomyces was not affected
by the X-rays, thus denoting an absence of Hertz waves in the
rays. Credit for the above result is due to L. Errera, from ex-
periments made at the Laboratoire Physique and the 1'Insti-
tut Solvay (Universite de Bruxelles).
163. GOSSART, CHEVALLIER, FOUTANA AND URUANNI'S EXPERI-
MENT, IN CONJUNCTION WITH J. R. RYDBERG. No MECHANI-
CAL ACTION OF X-RAYS. Comptes Rendus, Feb. 10, Mar. 23, Apr.
13, '96. From trans, by Louis M. Pignolet. The former party
alleged that radiations from a discharge tube caused a cessation
of the rotation of the vane of the radiometer. J. A. Rydberg
was not inclined to confirm such action. A. Fautana and A.
Uruanni made experiments and concluded that the action was
due to an electro-static force, having noticed that a Leyden jar
would also produce such effect. The author made some experi-
ments to determine the matter in reference to X-rays at a dis-
tance outside of the electro static field. The rays would neither
stop the vanes nor cause them to rotate. He made some other
experiments to detect whether there was any direct mechanical
power possessed by the rays; but if any, it was exceedingly feeble.
T. C. Porter made some experiments at Eton College, (Nature,
June 1 8, '96,) which confirmed the above results, finding that
the radiometer is entirely inert to the Roentgen rays, whether
they be from a properly electrically screened hot or cold tube.
He distinguished between the caloric conditions, for he found
that, not only will reduction of temperature vary the penetra-
ting power of the rays, 135 and 1520, but also will an increase
of temperature.
164. BATTELLI'S EXPERIMENT. X-RAYS WITHIN DISCHARGE
TUBE. Nuovo Cimento, Apr., '96, p. 193 ; Elect. Rev., Lon., June
12, '96. Shortly after the announcement of the discoveries of
Lenard and Roentgen, it would have been considered strange to
assert that X-rays may exist inside of the discharge tube. Bat-
telli certainly correctly infers, that inasmuch as X-rays appar-
ently originate from the point where a material object is struck
by the cathode rays, 115, it would follow that when the said
object is within the vacuum space, X-rays are propagated before
they reach the glass wall of the discharge tube. It has already
been noted (DeMetz, 630) that photographic action may be
i68
produced within the discharge tube. Battelli has confirmed
this, not by a crude experiment, like that (failure) of some au-
thority in England, but by a series of severe tests, leaving no
doubt as to the production of photographic action. He discov-
ered in connection with several subordinate phenomena that
among the rays capable of producing a photographic impression
within the discharge tube, some were deflected by a magnet and
others were not, from which he concluded that X-rays may exist
inside the tube, in conjunction with cathode rays, before col-
lision with the anti-cathode. The experiment consisted in de-
flecting the rays by a magnet, the film being in the path that
the rays would have had without a magnet. There was also a.
film in the path of the deflected rays. Protographic action was
produced upon both. He varied the vacuum. Photographic
action began at 3-10 mm., had its maximum at 1-70 mm., after
which it remained constant. No photographic action was ob-
tained upon a film placed within the tube opposite the anode,
except in one case where it was exceedingly weak. Lenard
continually inferred that there must be two kinds of cathode
rays. 75. Battelli has certainly sifted the two rays apart and
thus proved Lenard's conjectures. 6i, p. 47. The Elect. Rev. r
Lon., pays tribute to Battelli, by offering the following opinion :
" We have no hesitation in saying that Battelli, by means of in-
teresting and ingenious experiments, has made the greatest
advances in the theory of the X-rays since their discovery by
Roentgen."
In many cases the author has omitted stating, in taking scia-
graphs, that the films were protected from ordinary light by
opaque material. This, as a matter of course, has always been
understood. Battelli also had the films wrapped in material
opaque to ordinary light. Experimenters should, if possible,
always employ aluminum for this purpose, because the author
has alwas noticed that black paper or cloth permits a great deal
of light to come through, even when in double thickness.
Prof. Sylvanus P. Thompson ( The Electr., Lon., June 26, '96)
located a wire in a focus tube in the path of the rays between
the platinum reflector and the wall of the tube. Not only was
there a sciagraph of this wire produced in the sciascope, but also
the Crookesian shadow of the wire on the wall of the bulb.
For this experiment the exhaustion must be quite high. " At
no state of exhaustion did the platinum reflector convert all the
internal cathode rays into X-rays." Both shadows were cast
by the platinum reflector as the origin. More or less of the rays
between the reflector and the glass were sensitive to a magnet.
m
rn
170
165. BLEYER'S EXPERIMENT. COMBINED CAMERA AND SCIA-
SCOPE. Elect. Eng., July i, '96 ; Royal Ac ad. Med. &> Sur., of Na-
ples, Italy.- As early as April 7, J. Mount Bleyer, M.D., of
Naples, constructed and used the apparatus shown in the adjacent
cut, p. 169. The picture is self-explanatory. Attached to an
ordinary camera is a flaring sciascope, for receiving 1 the tempor-
ary sciagraph of the hand, for example. The X-rays are
converted into luminous rays by the fluorescent screen, and,
therefore, the camera will serve to take a picture by means of
the luminous rays from the sciagraph of the hand. The cut
represents also an induction coil and a discharge tube. Soon
afterwards, it was reported by an English paper that Dr. Levy,
of Berlin, and others of England, had also made similar tests
with success. In order to illustrate the applicability of the com-
bination, Dr. Bleyer took many sciagraphs with the camera.
He calls it the photofluoroscope, which, however, will probably
not meet with favor for the name does not suggest the nature
of the instrument. When two radically different devices are
combined into one, it is difficult to formulate an acceptable
single word, and, therefore, the instrument will probably always
be called by some of the following terms : A camera with scia-
scopic adjustment, or combined sciascope and camera, or corres-
ponding combinations with the word fluoroscope.
From the time that Roentgen's discovery was announced,
scientists throughout the world have made careful experiments,
up to date, in all possible directions, and the time has now come
when the number of experiments is rapidly decreasing, only one
or two being noted now and then in the scientific press, and
consisting mostly in repetition, with occasionally a slight de-
parture, involving a radically new subordinate discovery ; but
in view of the great number of scientists, and of their high
standing as careful experimenters, and because also of their
desire to be correct in their inferences, there might seem to be
little else to be investigated. Time only will tell. Before pas-
sing to the final chapters relating to other matters, a few more
experiments are related in the briefest manner.
1 66. Prof. Sylvanus P. Thompson confirmed non-polarization,
(Phil. So., June 12, '96, and The Electr., Lon., June 26, '96.)
Dr. John Macintyre (Nature, June 24, '96) carried on a long
series of experiments with tourmaline, and also arrived at the
conclusion that polarization of X-rays is practically impossible,
97, at end.
167. In the same paper Prof. Thompson showed conclusively
that there is a diffuse reflection of X-rays. Si and 103. A
H'
.5?
fc> B
o ,j
M O
172
curious experiment consisted in his obtaining dust figures, 36,
by the discharge of an electrified body by X-rays. In another
experiment he caused reflection of the rays from the surface of
sodium located in a vacuum. The amount reflected was a mini-
mum for normal incidence and increased at oblique incidence.
168. Prof. Oliver). Lodge, F.R.S., reported in The Electr.,.
Lon., June 5, '96, further detail experiments in the line set out
in 113. He proved conclusively, as stated by the editorial in
The Electrician, that a positive charge has increasing effect upon
the ray-emitting power of the surface exposed to the cathodic
radiation.
169. At Eton College, T. C. Porter (Nature, June 18, '96) con-
firmed the experiments of others by showing that the blackened
face of the thermopile connected with a very sensitive galvan-
ometer was not influenced in any manner by X-rays.
170. Prof. William F. Magie, of Princeton, N. J., made a care-
ful experiment in relation to diffraction. Princeton College Bul-
letin, May, '96. The experiment would certainly prove that if
X-rays are due to vibrations, the latter are of a different order
from those occurring in light rays, for the slits exhibited light
diffraction very well, but there was no evidence, by a widening
of the image on the plate, that X-rays had been diffracted in the
slightest degree. no and 1100.
171. Prof. Haga, of Groningen University, at the suggestion
of Mr. J. W. Giltay, (Nature, June 4, '96,) made some very
crucial tests, with numerous precautions, in reference to the-
action of X-rays upon selenium, and the results were so positive
that they thought that a practical application could be made by
using selenium for detecting X-rays, both qualitatively and
quantitatively. In repeating the experiments, it must be borne
in mind that one half hour or so is required for selenium to re-
turn to its former degree of ohmic resistance after being struck
by light or heat or X-rays.
Total number of to this place,
CHAPTER XIII.
A FEW TYPICAL APPLICATIONS OF X-RAYS IN ANATOMY, SURGERY,
DIAGNOSIS, ETC.
200. HOGARTH'S EXPERIMENT. NEEDLE LOCATED BY X-RAYS
AND REMOVED. The Lancet, Lon., Mar. 28, '96. Dr. Hogarth
is the medical officer of the general hospital, Nottingham.
A young woman was suffering with a pain in her hand near
the metacarpal bone of the ring finger. A slight swelling
existed. Ten weeks before, a needle had entered the palm
while washing the floor. It had entered at the base of the
fifth metacarpal bone. Chloroform had been given and an in-
cision made, but no needle found and its presence doubted. A
sciagraph was taken and the needle was accurately located and
the next day removed.
201. SAVARY'S EXPERIMENT. NEEDLE LOCATED BY SCIASCOPE
AND REMOVED. The Lancet ', Mar. 28, '96. Dr. Savary located a
needle by a sciascope although efforts by all other methods had
failed. A line was drawn between two points intersecting the
needle at right angles. About half an inch below the surface
of the skin of the wrist the blade of the scalpel impinged upon
the needle, which was removed without difficulty.
202. RENTON & SOMERVILLE'S EXPERIMENT. DIAGNOSIS. The
Lancet, Lon., Apr. 4, '96. A writer for the Lancet reported that
Drs. Renton and Somerville made a diagnosis with the assist-
ance of the screen. In one, the suspected case of unreduced
dislocation of the phalanx, they saw that the parts were in the
proper position. He showed to medical men an old fracture of
the forearm where the fragments of the bones were distinct as
to the shadows.
203. MILLER'S EXPERIMENTS. LOCATION OF BULLETS. Elect.
World, Mar. 21, '96. Bullets were clearly located in the hands
of two different men by Prof. Dayton C. Miller, of the Case
School of Applied Science. In one, the bullet had been lodged
for 1 4 years and had always been thought to lie between the
bones of the forearm, but two sciagraphs from different direc-
tions located the ball at the base of the little finger. By means
173
sr H
<
" a s
3* *
o o >
of five sciagraphs from different directions, the ball in the other
hand was located at the base of the thumb.
204. INJURIES BY ACCIDENT AND MISCELLANEOUS CASES. The
Integral, Cleveland, Ohio, '96. Many fingers and hands were ex-
amined by Prof. Miller that had been injured by planing ma-
chines, cog-wheels, base balls, pistols, etc., and in each case the
nature of the injuries was determined. Several cases of frac-
tured arms were studied some through splints and bandages.
Some sciagraphs indicated that the ends of the broken bones
had not been placed in apposition. Subsequently, an operation
was performed to remedy the setting. In one case, he scia-
graphed the arm from which a piece of the ulna had been
removed five years previously. The necrosis had increased.
Two sciagraphs at right angles to each other clearly exhibited
the nature of the disease. The permanent set of the toes by-
wearing pointed shoes was clearly exhibited (p. 30.) The figure
on page 147 is the side view of a foot in a laced shoe. The out-
lines of the bones can be traced, also the eyelets and the pegs
in the heel, while the uppers scarcely appear. In Fig. i (intro-
duction) is shown ahead, only the skull being clearly reproduced.
In the negative, the teeth appear and places whence the teeth
have been extracted, also the jaw bones, nasal cavities and the
ragged junction of the bones and cartilage. The varying thick-
ness is represented in the cut, at the temples and ears. Fig. 2
(introduction) shows that a broken bone was badly set, the ends
overlapping each other instead of meeting end to end. A scia-
graph of an elbow is shown on p. 161. The flesh is scarcely
visible. Fig. 3 (introduction) is a picture which reproduced the
mere indication of the spine and ribs. In the original negative
the collar bones, pelvis, clavicles, buckle of clothing and location
of the heart and stomach were faintly outlined. Fig. 4 (intro-
duction) is a representation of the knee of a boy 15 years old, in
knickerbockers, showing the buttons clearly, and dimly a 32
caliber bullet which is imbedded in the end of the femur.
2040. NECROSIS. Mortification of the ulna is represented oa
p. 142. Necrosis of the bone corresponds to gangrene of the,
soft parts ; life is extinct.
205. MORTON'S EXPERIMENT. DIAGNOSIS. Elect. Eng., N. Y.,
June 17, '96. Lect. before Odontological So., N. Y., Apr. 24, '96;
repeated in Dental Cosmos \ June, '96. Dr. William J. Morton, of
New York, made several important examinations of the human
system by the use of X-rays.
In regard to application in dentistry, he stated : " Each
errant fang is distinctly placed, however deeply imbedded
I 7 6
within its alveolar socket ; teeth before their eruption stand
forth in plain view ; an unsuspected exostosis is revealed ; a
pocket of necrosis, of sappuration, or of tuberculosis is revealed
in its exact outlines ; the extent and area and location of me-
tallic fillings are sharply delineated, whether above or below the
alveolar line. Most interesting is the fact that the pulp-cham-
ber is beautifully outlined, and that erosions and enlargements
may be readily detected."
206. The author saw one of Dr. Morton's original photo-
graphed sciagraphs of the thorax, 15 inches by n inches, not at
all creditably reproduced at page 161. In the original, to the
surgeon's eye : " The acromion and coracoid processes of the
shoulder blade are clearly shown in their relations to the head
of the humerus, or arm bone, and also the end of the clavicle,
or collar bone, is shown in its relations to the shoulder joint.
We have, in short, an inner inspection in a living person of this
rather complicated joint, the shoulder, and there can be no
doubt that in defined pictures of this nature even very slight
deformities and diseases would be detected. It is noticeable
that the front portions of the ribs are not shown, only the pos-
terior portions lying nearest to the sensitized plate appear ; also
the breastbone was sufficiently dense to almost entirely obstruct
the X-rays. A collar button at the back of the neck is taken
through the backbone. In some of my negatives the dark out-
line of the heart and liver is shown as well as the outlines of
tumors in the brain ; but this is evidently for purposes of dem-
onstrating the location of organs, an over-exposure, and does
not, therefore, indicate the outlines of the heart."
The time of exposure was reduced by the use of a fluorescent
screen in conjunction with the photographic plate.
207. A woman was troubled with a stiffened wrist. Dr.
Morton took a single sciagraph of both wrists side by side as
shown at page 174, (the photographic print being presented for
this book by E. B. Meyrowitz, 104 East 23d Street, N. Y.) The
injured wrist in the picture exhibited the Colles' Fracture
the ulna and radius bones being telescoped into their
fractured ends by a fall upon the sidewalk a year before. By
knowing the cause, the manner of cure became evident, and,
accordingly, the patient is expected to bend the wrist backward
and forward and laterally several times a day.
Dr. Morton, in a lecture before the Medical Society of the
County of New York, to be printed in the Medical Record, re-
lated that another promising field of research and application is
in the detection of calcareous infiltrations involving, for instance,
From sciagraph of club foot of child by Prof. Goodspeed. Copyright, '96, by
William Beverley Harison, Pub. of X-ray pictures, New York. This linograph (v/ood-
-cut), engraved and donated by Stephen J. Cox, Downing Building, 108 Fulton St.,
New York, affords an exact likeness of the sciagraph, well-nigh impossible ^y an
untouched half-tone.
i 7 8
the arteries, or occurring in the lungs and other tissues. Cal-
culi in kidneys, in the bladder, in the salivany ducts have
already been successfully located. The stages of ossification,,
and the eppihyseal relations of the osseous structure in children,
may be pictured as is demonstrated in the picture of the entire
skeleton of an infant five monts of age. The sciagraph shows
plainly that it will be possible to detect spinal diseases, either
in children or in adults. {Not reproduced^
208. NORTON'S EXPERIMENT. DIAGNOSIS. Elect. World, N. Y.,.
May 23, '96. In conjunction with Dr. Francis H. Williams, Dr..
Norton examined several patients from the city hospital to de-
termine how an X-ray diagnosis would agree with that previ-
ously made by the hospital staff. (See also 142, at end.) The
outline of an enlarged liver, ,7 inches in diameter, was easily
distinguished, the two outlines, .one by percussion and one b)r
X-rays, agreeing better in favor of the latter by ^ inch. AIL
enlarged spleen was perfectly outlined. The tuberculosis of
one lung caused it to be more opaque than the ', sound lung. It
was found necessary to take into account the seams of clothing,,
buttons, buckles, etc. A bullet was found exactly under the
spot which they marked as being over the bullet. A foreign
metallic body can be easily detected in the sesophagus, because
the latter is quite transparent. They could see the shadows of
the cartilaginous rings in the trachea, glottis, and eppiglottis.
Younger persons, up to 10 years of age, are more transparent;
than older.
209. LANNELONGUE, BARTHELEMY AND QUDIN'S EXPERIMENTS.
OSTEOMYELITIS DISTINGUISHED FROM PERRIOSTITIS. Elec. Rev.,,
Lon., Feb. 14, '96. In a sciagraph of a person diseased with the
former, the surface of the bone was proved to be intact, while
the internal parts were destroyed. In the latter disease the
changes proceed from the surface to the interior.
The art of sciagraphy, more nearly, as every month passes,
becomes developed by means of improved .apparatus, screens,
photographic plates and other elements which at present are
only dimly predicted. Nevertheless, how can a better sciagraph
of bones, showing their thickness and porosity, be desired than
that reproduced on page 177, and taken by Prof. Arthur W.
Goodspeed, and representing a club foot of a child ? In the
race to excel in this new art, no one, to the author's knowledge,
has surpassed Prof. Goodspeed, of the University of Penn., con-
sidered jointly from the standpoints of priority, superiority, quan-
tity and variety. Dr. Keen, L.L.D., Professor in the Jefferson
Medical College, of Philadelphia, stated (Inter. Nat. Med. Mag.+
179
June, '96) that Prof. Goodspeed " has far eclipsed all others in
these most beautifully clear skiagraphs."
210. A book could be filled with the numerous cases of diag-
nosis by X-rays showing the utility. In closing this chapter,
let it suffice to mention some of the sources of literature relating
to this subject directly or indirectly : location of shot (by Dr.
Ashhurst, Phila.) in lady's wrist, not located by other means.
Dr. Packard's case of acromegaly ; Dr. Muller's (Germantown)
location of needle in boy's foot ; cause of pain not before known ;
needle subsequently removed ; a perfect thorax, or trunk, by
Prof. Arthur W. Goodspeed, University of Pennsylvania; Thomas
G. Morton's (M. D. Pres. Acad. Surg., Phila.) application to
painful affection of the foot, called metatarsaligia. All of the
above noticed in Inter. Med. Mag. y June, 1896. Case of a burned
hand with anchylosis of the fingers, by W. W. Keen, M.D.,
L.L.D. Bacteria not killed by X-rays. Normal and abnormal
phalanx distinguished. Fracture and dislocation sometimes
differentiated by X-rays. Amer. Jour. Med. Sci., Mar., '96.
CHAPTER XIV.
THEORETICAL CONSIDERATIONS.
Before attempting to discuss the facts now known in regard
to the Roentgen phenomena, it is well to review briefly the
known ways in which radiant energy may be transmitted.
By radiant energy is, of course, meant energy proceeding out-
ward from a source and producing effects at some distant point.
There are two well understood ways in which energy may be
transmitted, first, by an actual transfer to the distant point of
matter to which the energy has been imparted from the source,
as in the flight of a common ball, a bullet, or a charge of shot.
In this mode of transmission, it is evident that the flying par-
ticles, assuming that they are subject to no forces on the way,
will move in straight lines from the source to the distant point.
They constitute real rays, diverging from the source ; an ob-
stacle in their path, would, if the radiations proceeded from a
point, cast a shadow with sharply defined edges.
Second, by a transfer of the energy from part to part of an
intervening medium, each part as it receives the energy, trans-
mitting it at once to the parts around it, no part undergoing
more than a slight displacement from its normal position. This
mode of transmission constitutes wave motion. The source im-
parts its energy to the particles of the medium near it. Each
of those particles transfers its energy to the particles all around
it. Each of these particles in turn transfers its energy to the
particles around it, and so on through the medium. It is plain
that there are here no such things as genuine rays. As the
energy is transferred from particle to particle, each in turn be-
comes a centre of disturbance transmitting its motion in all di-
rections. It is only because the movements transmitted from
different points annul one another except along certain lines,
that we have apparent straight lines of transmission, and, there-
fore, fairly sharp shadows. But shadows produced by wave
transmissions are never absolutely sharp. The wave movement
is always propagated to some extent within the boundary of the
180
geometrical shadow, less as the wave lengths are shorter. With
sound waves whose lengths are measured in inches or feet, the
penetration into the shadow is considerable. With light waves
Yrfonr to TTrtanr of an incn m length, the penetration into the
shadow is very small and requires specially arranged apparatus
to show that it exists.
This penetration into the geometrical shadow is characteristic
of energy propagated by wave motion, and if the fact of such
penetration can be demonstrated, it is conclusive proof of pro-
pagation by waves.
Another characteristic of wave motion is found in the phe-
nomena of interference. This is the mutual effect of two
wave systems, which, when meeting at a given point, may
strengthen or annul each other according to the conditions under
which they meet. Either of those characteristics should enable
us to distinguish between propagation by wave motion and by
projected particles. But when wave lengths are very short and
radiations feeble, the tests are not easy to apply.
Again, a wave is in general propagated with different veloci-
ties in different media. This causes a deflection or deformation
of the wave as it passes from one medium into another, and re-
sults in refraction, as in the cases of light and sound. Absence of
refraction would be strong though not conclusive evidence
against a wave theory of propagation.
In wave propagation, each particle of the medium suffers a
small displacement from its equilibrium position and performs
a periodic motion about that position. This displacement may
be in the line of propagation longitudinal vibration or it may
be in a plane at right angles to that line transverse vibration.
All the phenomena mentioned above, diffraction, interference,
refraction, and also reflection, belong equally to either mode of
wave propagation. Other phenomena must be made use of to
distinguish between these.
When the vibrations are transverse they may all be brought
into one plane through the line of propagation. They may be
polarized, when the ray will present different phenomena upon
different sides. When the vibrations are longitudinal, no such
phenomena can be produced. Polarization, then, serves to dis-
tinguish between longitudinal and transverse vibrations.
Now let us consider briefly the Roentgen ray phenomena that
bear upon the question of the nature of the propagation.
It seems to be settled beyond question that the origin of the
Roentgen rays is the fluorescent spot in the discharge tube.
107, 108, in. The evidence seems overwhelming that within
/
FROM SCIAGRAPH OF NORMAL ELBOW-JOINT ; STRAIGHT, IN POSITION OF
SUPINATION.
By A. W. Goodspeed. Phot. Times, July, '96.
Copyright, 1896, by William Beverley Harrison, Publisher of "X-ray" Pictures, New York.
-i8 3
the tube, the phenomena are the result of streams of electrified
particles of the residual matter, shot off from the cathode in
straight lines, perpendicular to its surface. 57. This was
Crookes' original theory, 53, near centre^ and it seems to have
stood well the test of scientific criticism. These flying particles
falling upon anything in their path, give rise to X-rays. It is
preferable, but not essential, that the bombarded surface should
;"be connected electrically with the anode. 113, and 116.
The best results are obtained by using a concave cathode, and
placing at its centre the surf ace which is to receive the bombard-
ment, thereby concentrating the effect upon a small area.
Nearly all experimenters agree in locating the origin of the
X-rays at this bombarded spot. The energy here undergoes a
transformation, and the X-rays represent one of the forms of
energy developed.
What are the characteristics of this particular form of radiant
energy ?
It causes certain salts to fluoresce, 66, 84, and 132, and it
; affects the photographic plate. 70 and 84. In these respects,
it is like the short wave length radiations from aluminous source.
= It is, however, totally unlike these in its power of penetrating
numerous substances entirely opaque to light, such as wood,
paper, hard rubber, flesh, etc. In passing through hard rubber
and some other opaque insulators, X-rays are like the long wave
length radiations from heated bodies, but X-rays penetrate many
substances that are opaque to these long wave length radiations,
and they are especially distinguished from all forms of radiant
energy previously recognized, in their relative penetrating
power for flesh and bones which makes it possible to obtain the
remarkable shadow pictures which have become within three or
four months, so familiar to all the world.
But these phenomena, although they serve to distinguish the
X-rays from all other forms of radiant energy, do not furnish
any clew to the nature of the X-rays themselves.
In attempting to formulate a theory of X-rays, the idea that
first naturally presents itself is that they are due to some form
of wave motion.
The characteristics of wave motion are diffraction and inter-
ference phenomena. So far, no positive evidence of diffraction,
no, nor interference, 89, have been recognized, although
experiments have been tried "that would :have. shown plainly,
diffraction phenomena, had light been used in place of the
Roentgen radiations. 170. We must, therefore, conclude,
either that the Roentgen radiations in the experiments were
FROM SCIAGRAPH OF KNEE-JOINT, STRAIGHT, SIDE VIEW, SHOWING
PATELLA, OR KNEE-CAP.
By Prof. Goodspeed. Phot. Times, July, '96.
1 85
too feeble to produce a record of the diffraction effects, or, that
they are not due to wave motion at all, unless of a wave length
very small even when compared with waves of light. The
absence of refraction is also opposed to any wave theory of the
Roentgen radiations, for it is difficult to believe that waves of
any kind could travel with the same velocity through all media,
which they must do if they suffer no deviation. 86.
The next supposition naturally is, that the phenomena are due
to streams of particles. It has been suggested that the rays
may be streams of material particles, but this theory cannot be
maintained in view of the fact that the rays proceed, without
hindrance, through the highest vacuum. 72 b and 133, near
end. Neither is it consistent with the high velocity of propa-
gation. Molecules of gas could not be propelled through air with
any such velocity or to any such distance as X-rays are propa-
gated. Tesla has claimed 139, that the residual gases are
driven out through the glass of the vacuum bulb by the high
potential that he employs. This has not been confirmed by
other experimenters. It has been observed that the vacuum
may be greatly improved by working the bulb, 121, that is,
sending the discharge through it, but experimenters generally
have found that heating the bulb impairs the vacuum and
restores the original condition. The gases, were, therefore,
occluded during the electrical discharge, to be again set free by
heating the bulb. 139 . The rays may be ether streams,
perhaps in the form of moving vortices, but of such streams we
have no independent knowledge, and can only determine by
mathematical analysis, what their characteristics should be.
They would not suffer refraction, and would not produce inter-
ference nor diffraction phenomena. Whether they would do
what the X-rays do, go through the flesh and not through bone,
through wood and not through metal, excite fluorescence, or
affect the photographic plate, cannot be said. There is evidence
that there are at least two kinds of X-rays, 152, differing in.
penetrating power, though perhaps not differing in other re-
spects.
X-rays have their origin only in electrical discharges in high
vacua. They are absent from sun-light and from light of the
electric arc, and other sources of artificial illumination, 136.
Proceeding from the bombarded spot, they are not deflected by
a magnet, except in an evacuated observing tube, as proved by
Lenard, 720, and show no evidence of carrying an electric
charge like cathode rays, 61 b, p. 47. On the contrary, they
will discharge either a negatively or positively charged body in
FROM SCIAGRAPH OF NORMAL KNEE-JOINT, FLEXED.
Phot. Times, July, 96.
Copyright, 1896, by William Beverley Harison, Publisher of "X-ray " Pictures, New York.
i8 7
their path. The evidence seems conclusive (Chap. VIII.) that
the ultra-violet rays from an illuminating source also discharge
charged conductors. In this respect, therefore, there is a simil-
arity between the X-rays and ultra violet light.
The action of the waves of light upon a cell formed of selenium
lowers the resistance of the latter and herein is circumstantial
evidence at least, concerning the similarity of the properties of
X-rays and light, because the former are also found to increase
the conducting power of selenium. 171.
The experiments of Roentgen, 90, seem to show that the
discharging effect of X-rays is due to the air through which the
rays have passed.
It is certain that the discharge of electrified bodies by light
occurs more generally for negatively than for positively charged
bodies, 99 B, 99 /, and 99 S, that it depends upon the nature,
97 , and density, 97 a, of the gas surrounding the body, and
also upon the material of the charged body itself. 98. The
discharge would, therefore, seem to be connected with a chem-
ical action, 153, near end, which is promoted by the rays. This
seems all the more probable, since it was found, 98, that the
more electro-positive the metal, the longer the wave length that
would influence the discharge. In this connection, it is well to
note that Tesla found, 1460, that in their power of reflecting
(or diffusing X-rays), the different metals stand in the same or-
der as in the electric contact series in air, the most electro-
positive being the best reflectors. It would be interesting to
know whether connecting the reflecting plate to earth, would,
in any way, vary its reflecting power.
The X-rays seem to discharge some bodies, when positively
charged, and other bodies when negatively charged. They will
also give to some bodies a positive, and to others a negative
charge ( 90 c]. Is the order here also that of the electrical contact
series in air ? Are not all the phenomena of electrical charge
and discharge, of reflection or diffusion, and of X-rays, connected
with chemical action, as the apparent difference of potential, due
to contact, undoubtedly is? 153.
An experiment by La Fay ( 139 a) seems to show that X-rays,
in air, after passing through a charged silver leaf, acquire the
property of being deflected by a magnet, as are the cathode rays
inside the generating or exhausted observing tube, 720. If
this is confirmed, it would go far to support the theory that
these rays are streams of something.
The burden of proof, up to the present, seems to be against
any wave theory of the X-rays, for, although they are like the
FROM SCIAGRAPH OF HEAD BY PROF. GOODSPEED. NASAL BONES APPEAR
LIKE EYELASHES.
Inter. Med. Mag-,, June, 96.
The cervical vertebrae are distinguishable in the original, but barely so in the half-tone.
Fillings are located.
189
ultra-violet rays in producing fluorescence and in affecting the
photographic plate, and have some points of similarity to these
rays in their effect upon charged bodies, the X-rays are totally
unlike the ultra-violet, in respect to diffraction and interference
phenomena. In fact, the absence of such phenomena, if they
are really absent, is conclusive proof that the X-rays cannot be
wave motions, unless of a wave length extremely short even as
compared to waves of light.
Since writing the above, I have seen an account of experi-
ments in relation to diffraction of X-rays, presented to the
French Academy by MM. L. Calmette and G. T. Huillier, in
which the authors claim to have obtained evidence that diffrac-
tion occurs. The following translation of MM. Calmette and
Huillier's paper is taken from the Electrical Engineer, N. Y., for
July 22, 1896.
"We have the honor of submitting to the Academy some pho-
tographic proofs obtained with the Rontgen rays by means of
the following arrangement."
" Very near the Crookes tube there is a screen " E " (diagram
omitted}, of brass, perforated by a slit, the width of which has
rarely reached a half mm. A second metal screen, E', is formed
of a plate provided with two slits or pierced with a window in
which is fixed a metal rod of i mm. in diameter. This screen
is placed at the distance, a, behind the former. Lastly, a photo-
graphic plate, enfolded in two leaves of black paper, is placed at
the distance, b, behind the second screen, E'."
" The following table indicates, for each proof, what is the
screen E' used, and the value of a and b -\- a \
i. Rod of i mm. in diameter ................... 5 19.5
3- " " ... ................. 5-5 20
5- ................... 8.9 30
7. Two narrow slits, separated by a cylindrical
rod of i mm. in diameter ................. ? ?
" On the proofs i, 3, 5 the shadow thrown by the metallic rod
is bordered on each side by a light band which shows a maxi-
mum of intensity. Within this shade we observe a zone less
dark, which seems to indicate that the Rontgen rays penetrate
into the geometrical shadow. Lastly, in proofs 3 and 5 we see,
in like manner, a maximum of intensity along the margins of
Ihe window in which the rod is placed."
" In the proof No. 7 we perceive, in the middle of the two
190
white bands, a fine dark ray, while in the shadow of the rod
which separates the two slits there is seen a light ray."
" If we compare these results with those obtained with light
in the same conditions, the slit being relatively wide and the
intensity weak, it seems difficult not to ascribe them to the
diffraction of the Rontgen rays."
" The proofs obtained in these experiments which we pro-
pose to continue are not yet so distinct that we can measure
the wave length with any precision. But we are still led to
believe that this wave length is greater than that of the lumin-
ous rays. Comptes Rendus" Of course, if diffraction phenom-
ena can be demonstrated, the question as to the radiations
being wave propagations, is settled, though the question whether
the vibrations are longitudinal or transverse, is still open.
Before accepting any stream or vortex motion theory, we need
to know more about the X-ray phenomena, and more about
stream and vortex motion.
MAY 9 1933
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