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Born in Holland, 1845. 
From a photograph by Hanfstaengl, Frankfort-on-the-Main. 




OF THE'"' 





Mem. Amer. Inst. Elec. Eng. 

Mem. Amer. Soc. Mech. Eng. 

Author of "Inventing as a Science and an Art." 




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. 




Cooyright, tSge, 


Temple Court Building, New York. 

^t 7 


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 

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- 


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 


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- 


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 

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- 


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. 

August, 1896. 




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 

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. 


20. Relation of Light to Electricity. The Square Root of the Dielectric 

Capacity Equal to the Refractive Index. 


21. Hermetically Sealed Discharge Tubes with Platinum Leading-in 


22. Luminosity of Discharge Tubes Produced by Rubbing. Increased 

by Low Temperature GEISSLER 

23. Different Vacua Needed for Luminosity by Friction and by Dis- 


24. Phenomena of Discharge around the Edges of an Insulating Sheet. 


25. Highest Possible Vacuum Considered as a Non-conductor. ..MORGAN 

26. Constant Potential at the Terminals of a Discharge Tube. 


260. Polarity of Discharge-tube Terminals in Secondary of Ruhmkorff 
Coil. Mathematical Deductions , KLINGEN-BERG 

27. Pressure in Discharge Tube Produced by a Spark. 



28. Actions of Magnetism upon the Arc and Flame. 


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 

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 


34. Electric Images RIESS 

35. Electrographs on Photographic Plate by Discharge. 


36. Positive and Negative Dust Pictures upon Lines Drawn by Elec- 


360. Photo-electric Dust Figures HAMMER 

36^. Dust Portrait HAMMER 

37. Electrical Images by Discharge Developed by Condensed Moisture. 

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 



41. Discharge Tube in Primary Current. Striae. Least E.M.F. Required. 


42. Current Interrupted Inside of Discharge Tube instead of Outside. 


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. 


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 


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. 


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. 


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 




-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. 

65, end of page 53. Properties of Cathode Rays in Open Air. ... ..LENARD 

66. Phosphorescence by Cathode Rays Outside of the Discharge Tube. 

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. 


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 


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. 


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 


\ 84. X-rays Characterized. Fluorescence and Chemical Action. 


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 .ROENTGEN 

87. Non-double Refraction Proved by Iceland Spar and Other Materials. 


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. 


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 

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. 


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. 


98. Negatively Charged Bodies Discharged by Light. Discharge from 

Earth's Surface Explained by Inference and Experiment. 


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 


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. 


loirt. Sciagraph Produced through 150 Sheets of Photographic Paper. 


102. Discharge Tube Adapted for Both Unidirectional and Alternating 

Currents ........................... THOMSON, E. , and, SWINTON 

103. X-rays. Opalescence and Diffusion. 

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. 


107. Source of X-rays Determined by Projection through a Small Hole 

upon Fluorescent Screen Adjustable to Different Positions. 

io7<z. Use of Stops in Sciagraphy .................... LEEDS and STOKES 

107^. X-rays from Two Phosphorescent Spots. 


108. Source of X-rays Determined by Shadows of Short Tubes ..... STINE 

109. Instructions Concerning Electrical Apparatus for Generating X-rays. 

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. 


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. 


115. X-rays Equally Strong during Fatigue of Glass by Phosphorescence. 


\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 


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. 


122. External Electrodes Cause Discharge through a Higher Vacuum 

than Internal EDISON 

123. Profuse Invisible Deposit from Aluminum Cathode. 

f s *24. Possible Application of X-rays. Fluorescent Lamp. 


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. 


^28. Differences between X-rays and Light Illustrated by Different Pho- 
tographic Plates. Times of Exposure. 


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. 


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. 



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. 

139/5. Penetration of Molecules into the Glass of the Discharge Tube. 


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 


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. 


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 


151. Sciagraphic Plates Combined 'with Fluorescent Salts. 


152. Penetrating Power of X-rays Varies with the Vacuum. 


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. 

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- 

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. 


161. Mineral Substances Detected in Vegetable and Animal Products. 


162. Hertz Waves and Roentgen Rays Not Identical ERRERA 

163. Non-mechanical Action by X-rays Determined by the Radiometer. 


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 


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. 



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. 


209. Osteomyelitis distinguished from Perriostitis. 


210. Concluding Miscellaneous Experiments Relating to Similar Applica- 

tions of X-rays. 



Theoretical Considerations, Arguments, and Kindred Radiations. 



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. 


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. 


(Due to defective setting.) 


FIG. 3. RIBS. 


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 

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. 


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. 

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. 

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. 

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. 

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. 

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. 

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. 

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. 

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. 

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. 

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 


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. 

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. 

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 

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 


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. 

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. 

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. 

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. 

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 


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. 

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 


in connection with other results, especially those obtained, that 
his theory is probably correct. 

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. 

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. 

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. 

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 


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. 

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- 


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. 

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. 

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 


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 


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. 


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. 


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. 

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. 



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. 

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." 

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 / 



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 

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. 


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. 

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 

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. 




Taken by Prof. McKay. 


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. 

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. 



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. 

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. 


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. 


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. 

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 


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. 

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 ? 

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. 


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- 



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." 

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- 

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 


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. 

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. 

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. 

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 


By Prof. Miller. 



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 

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- 


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. 

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. 

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 


-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. 


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. 

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. 

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,. 


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. 

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- 


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." 

co> % 


M o 

X c 
M g 


U u 



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 


-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. 

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. 

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 


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. 

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. 

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. 

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 ? 


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. 


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. 



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. 

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, 


deduction of their principles and formulation of an ingenious 

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." 



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." 

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 




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 


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 





a 1 er ff 




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. 

ULAR CHEMICALS BY CATHODE RAYS. Nature, Lon. Feb. 21, '95, 


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 

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 

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. 

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. 



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 

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- 



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. 

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. 

63^. The conclusion arrived at by mounting the phosphore- 
scent screen in different positions and at different angles as well 


as by observance of the gaseous luminosity, was that the alum- 
inum window scattered the rectilinear parallel cathode rays in 
all directions, 57. 

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. 


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 

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 


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. 

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- 


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. 

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, 


Copyright, 1896, by William Beverly Harison, pub. of X-ray pictures, 
59 Fifth Ave., New York City. 


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, 


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. 

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. 


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 


By Leeds and Stokes. 


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 

FUSED. He discovered the remarkable property, contrary to his 


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. 

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 


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, 

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 


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. 



137, p. 136. 


Wurz. Physik. Med. Gesell. Jan. '95 ; Nature, Lon. Jan. '96 ; The 
Elect. Lon. April 24, 96; Sitz. Wurz. Physk. Inst. D. Uni. Mar. 
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. 

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. 



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. 

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^. 


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. 

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. 

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 


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. 

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. 

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. 


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. 

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 

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. 


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,' 


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. 

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. 

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. 

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. 


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. 

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. 


9, '96, an account of his focus tube, the Kings College published 
a description of an exactly similar one, represented in the cut. 


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. 

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. 


(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 

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 


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- 


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- 

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. 


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. 


OF LIGHT. Berlin Akad. II 
p. 983. English translation of the 

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 



were afterwards confirmed by many, and sub-ordinate discov- 
eries originated. 98-99 T. 


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. 

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- 


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. 

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 


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. 

GLOWING ELECTRIFIED BODY. Wied. Ann., XXXIII., p. 454, '88. 

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. 

PRODUCED BY LIGHT. Note 2-4, Rend. R. Acad. die Lincei, May 
6, 20, and June 3, '88. 

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. 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. 

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. 

SION THROUGH AIR, Comptes Rendus. CVI, pp. 1,349 to 51. 
88. They employed arc lamps whose carbons had aluminum 

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. 

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 


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. 

CX, pp. 751 to 754. '90. 

DUCED BY ILLUMINATION. Luer's Rep. XXV, pp. 380 to 
382. '89. 


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 

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. 

SMALL FLAME EMPLOYED. Bihang till K. Svenska Vet.-Akad. 
Hand. 15, Afd. i, No. 4, p. 30, '89. 

FICATION BY FLAMES. Brit. Asso. Rep., '90, p. 225. 

VACUA. 99^/, near end. Proc. Ro. So., LXVII., p. 118. 

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. 

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. 

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. 

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. 


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- 

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 ; 





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. 

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 : 

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 


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 


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. 

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. 

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- 


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. 

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. 


_>^ PLATE 

^ 5 | 

RICE'S EXPERIMENT. FIG. i, 106, p. 99. 

RICE'S EXPERIMENT. FIG. 2, 106, p. 99. 

Taken with the above apparatus. 


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. 

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. 

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- 


STINE'S EXPERIMENT. FIG. i, 108, p. 103. 

STINE'S EXPERIMENT. FIG. 2, 108, p. 103. 


produce but one strong focus upon the platinum. Elect. World, 
N. Y., May 23, '96. 

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. 

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- 

n ' 

( > i 

1 A 

1 r 





. ' i 


1 1\ 

1 ^ 


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 


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. 


159. NON- REFRACTION. Refraction was attempted with pris- 
ims of paraffine and of wax, but no refraction was noticed. 

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 


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. 

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 


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). 

Comptes Rendus, Mar 23, '96. From Trans, by Louis M. Pigno- 
let. He also confirmed that X-rays radiate from the phosphor- 
escent spot. 

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. 

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 


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." 


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, 


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 


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. 

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. 

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. 

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." 

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. 


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. 

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- 


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 


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. 


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.) 

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.) 



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, 



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 


was thought, to the fact that the construction embodied the 
combination of internal and external electrodes. 121. 

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 


24 hours, after which X-rays coulu not be generated until the 
discharge had been continued for 4^ hours. 

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. 


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 


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 


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. 


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. 

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. 

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 


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. 

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." 

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. 



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. 

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- 

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. 

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. 

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, 


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. 

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 


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 


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. 

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- 


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..^ 


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. 

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. 

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. 

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 


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 


By Leeds and Stokes. 


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. 

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 


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. 


137. TESLA'S EXPERIMENTS. Elec. Rev., N. Y., March n, '965, 
page 131, March 18, page 147, April i, page 171, and April 8, 
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 

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 


(CUT AT p. 81) AND TESLA SYSTEM. 137, pp. 136 and 138. 


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. 

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. 

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 


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. 

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. 

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 

Observed by means ol a photograph, in 1882, by William J Hammer. 


From sciagraph by Prof Miller. 


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. 

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- 


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. 

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 


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.). 

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 


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. 

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 


In the course of Tesla's experiments, he observed that the 

By Prof. Miller. 


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. 

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 

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 


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 


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 


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. 

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." 

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- 


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. 


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 

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 


By Prof, Goodspeed. Photo. Times, July, '06. 


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 

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. 


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 


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. 

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. 

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- 

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. 

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. 



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 

By Prof. Miller. 


fluorescent bodies in combination with the photographic plate,, 
and found that potassium platino cyanide was decidedly the best. 

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. 

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. 

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." 

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. 

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. 



Comptes Rendus, Feb. 24, 96. From trans, by Louis M. Pigno- 
let. Sciagraphs taken by the X-rays showed that diamonds be- 


By Prof. McKay, Packer Institute. 


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 

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. 

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. 

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. 

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. 

THEREIN. Comptes Rendus, Mar. 23, '96. A sciagraph taken with 


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. 

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. 


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 

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 

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). 

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. 

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 


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 

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. 




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 



fc> B 

o ,j 

M O 


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 

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, 



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. 

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. 

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. 

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 


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. 

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. 

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^ 

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. 

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.+ 


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. 



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 


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 




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 


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- 

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 


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 



Inter. Med. Mag-,, June, 96. 

The cervical vertebrae are distinguishable in the original, but barely so in the half-tone. 
Fillings are located. 


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 


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 
DEC 26 1935 

, o>G W 
tf R *" 


DEC 18 193i 

7 1969 7 4 

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LD 21-50w-l,'33 


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