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\_Sept. 18 , 1879 

sation' corresponds to blue and yellow, the blue rays ex¬ 
citing it in one direction and the yellow rays in the other. 
The other source corresponds to red and green, and is 
excited in like manner. It will at once be seen with what 
admirable simplicity this will explain colour-blindness, 
avoiding the violence done to the evidence by the Young- 
Helmholtz doctrine. Normal-eyed persons possess both 
sources of sensation ; colour-blind persons possess only 
one. The usual case is when the red-green source is 
absent, the patient seeing only blue and yellow; but the 
other defect is possible, giving blindness to blue and 
yellow, and vision only of red and green; and Dr. Stilling, 
who strongly espouses the theory, states that rare examples 
of this have been found. If both sources of sensation 
are absent, the patient sees only light and shade, and 
this case also is said to have been practically known. 

It is a pity Dr. Jeffries has omitted to mention this 
theory, which, if it should be substantiated by further 
inquiry, 1 bids fair to be a most valuable, contribution to 
our knowledge. In the meantime the phenomena of 
colour-blindness, from the important bearing they have 
on the nature of colour-perception generally, require much 
further careful investigation. 

William Pole 


Elementary Lessons on Sound. By Dr. W. H. Stone, 

Lecturer on Physics at St. Thomas’s Hospital. (London: 

Macmillan and Co., 1879.) 

SINCE the publication, some five and twenty years ago, of 
Helmholtz’s great work on musical acoustics, the study of 
the nature of sound has become popular. The ordinary 
phenomena of hearing must interest every one ; but it is 
to the thoughtful student of music that the subject pre¬ 
sents its chief attractions. We cannot imagine any intel¬ 
ligent musician who will not be desirous to know some¬ 
thing of the foundation of the wonderful fabric he has to 
deal with, and to learn how the principles of science bear 
on the practice of the art. 

It is well, therefore, that Messrs. Macmillan have in¬ 
cluded among their School Class Books one which gives, 
in a very small compass, a large amount of information 
as to the law's and phenomena of sound. The author has 
not only extracted the essence of what is contained in 
bulky and expensive treatises, sometimes in foreign lan¬ 
guages, but he has also given much additional information 
from memoirs and transactions of scientific societies out 
of the reach of the ordinary public. 

The application of acoustics to musical instruments is 
a useful addition, the subject being one which the author 
has made specially his own. He has also stated some 
of the simplest facts of the connection between acoustical 
phenomena and the structure of music ; but this is too 
wide a subject, and involves far too complicated con¬ 
siderations to be fully dealt with in an elementary work of 
this kind. 

We notice a few trifling errors, as, for example, on page 
3, the monochord can hardly be said to be “ named after” 
Pythagoras; and Tartini’s terms suono was intended by 
him rather as a guide to correct double-stopping than 
“tuning.” On page 11, line 7, the expression “first 
partial” is probably meant to be “first overtone.” On 
page 76 a pretty contrivance, by Mr. Francis Galton, is 
ascribed to Capt. Douglas Galton. These things are, 
however, of little consequence. 

It may be mentioned that one of the main points in the theory has iately 
received unexpected and powerful support from the brilliant discoveries of 
.oeli and Kuhnein regard to the physiology of the retina. 


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Local Colour-Variation in Lizards 

The interest which some notes by Messrs. Wallace and' 
Giglioli (published in Nature) have "called forth with regard 
to the local variation of colour in reptiles causes me to publish 
these few lines. 

Since the year 1874 I havebeen carefully studying this subject, 
and therefore wish to remove the generally prevailing opinion 
that no endeavours have yet been made to explain it. 1 have 
not thought it necessary to write this before, thinking that my 
works touching this subject were known to naturalists, or -would 
have become known through the mention Mr. Carpenter makes 
of them. Such, however, is not the case. Neither English 
nor Italian zoologists have taken any notice of the newer German 
publications concerning the local variation of colour in lizards. 
They content themselves with merely mentioning many new and 
truly interesting instances of this variation, but leave unnoticed 
all attempts made to obtain an explanation of the same. 

The first effort to explain this appearance was made by Mr. 
Eimer in 1872, at the time that the beautiful black and blue lizard 
was discovered on the Faraglioni rocks, near Capri. Prof. 
Eimer tries to explain this change of colour in the Lo.certa 
muralis (which is green both on the Continent and the Island of 
Capri) by attributing it to an adaptation to the colour of the 
Faraglioni rocks. However, as those rocks are not of a bluish- 
black, but rather a yellowish-reel colour, intermixed with a little 
gray, and as, moreover, the lizards there have no enemies against 
which they require protection, and therefore no adaptation is 
necessary, I considered Prof. Elmer’s explanation a failure, and 
at the same time I tried to confirm by fresh facts my hypo¬ 
thesis made in 1874 (“ Usher die Entstehung der Farbenbei den 
Eidechsen,“ Jena, 1874). This hypothesis, which, it is true, has 
till now met with little approval, is as follow's :—The skin of the 
lizard has two layers of pigment. The black pigment, which 
lies lowest, gets the power, under the concentrated influence of 
the sun, to leave its motionless state, and is made to rise by the 
contraction which the nerves exercise on the cells containing it, 
and by forcing itself more or less upwards through the elements 
of the pale layer of pigment, gives us the impression of different 
colours. That change of colour which we are able to observe in 
chameleons in a short space of time, under the condition of a 
frequent change of light, takes place with lizards only in the 
course of ages, embodying itself in manifold degrees of develop¬ 
ment, and provided the animal does not change the locality, 
remains as a distinguishing characteristic of the form. If, how¬ 
ever, the lizard changes its locality, if it is isolated on a rock 
or islet which has separated itself from the mainland, and is en¬ 
tirely and constantly exposed to the rays of the sun, as must 
naturally be the case on rocks which, like the Faraglioni or the 
Island of Ayre, are void of all vegetation, in that case, I say, the 
black layer of pigment is set in motion, and by constant suc¬ 
cessive risings to the surface at last gains a definite superposition 
over the yellow pigment, as has been the case with the black 
Faraglioni and Lilfordi lizards. 

This phylogenetic development of colours can be traced (as I 
have already mentioned in the year 1874) by the individual deve¬ 
lopment of colour ill the lizard, but necessarily only under the 
constant strong influence of the sun on young individuals. Dr. 
Braun, in his work on the Lacerta lilfordi, informs us that the 
young lizard of the Island of Ayre has exactly the same colour as 
its typical form on the larger Balearic islands, and only turns 
black in the course of its growth. 

Though we can only observe the turning black of these lizards 
in the individual growth of the animal, we can obtain a returning 
of the full-grown animals to their original paler colours by arti¬ 
ficial means, that is, by preventing the rays of the sun from 
falling on them perpendicularly. By these means ’I completely 
discoloured numbers of the Faraglioni lizards and the brown ones 
from the island of Ponza. The former turned bluish-green, the 
latter brownish-green. 

Before I pass on to an enumeration of the above-named trails- 

© 1879 Nature Publishing Group 


Sept . 18 , 1879 ] 

formed lizard--, I shall just mention a third endeavour which has 
been made to explain the black colour of the lizards inhabiting 
small islets. 

In his interesting book, “ Beitrage zur Descendenz-Tkeorie,” 
Leipzig, 1876, Seidlitz has tried to introduce the belief that the 
black colour serves as an armour or protection to the animal 
against the burning rays of the sun,' Thereupon. I sought to 
prove that reptiles inhabiting the desert would need such a pro¬ 
tection more than the others, yet they are not black. 

As some might perhaps draw, from what I have said, the 
conclusion that, according to my hypothesis the reptiles of the 
desert should be also black, I must remark that the scorching 
rays of the sun in the desert effect so strong rn elevation in the 
temperature of the soil, that it brings forth a relaxation in the 
animal, and slackens the energetic movement of the pigment, 
consequently the extreme heat counteracts the effect which the 
light produces, whilst on the islets of the Mediterranean the heat 
is alleviated by the sea breezes and by a certain degree of damp¬ 
ness. As we already know, all our European species of lizards 
carefully avoid the desert. 

The dark-coloured lizards at present known, which inhabit 
small islands, are the following ones :—- 

1. Lacerta muralis, var. archipelagic a, De Bedriaga: “Die 
Faraglioni-Eidechse.” {Heidelberg, 1876; pp. 19.) L.muralis, 
var. B. Erhard : “ Fauna der Cykladen,” (Leipzig, 1858; pp. 
80.) L. muralis, var. C., Sclireiber: “ Herpetologia europsea.” 
(Braunschweig, 1875 ; pp. 408.) L. muralis, var. archipelagica, 
V. Bedriaga : “ Herpetologische Sfudien,” im Archiv fiir Natnr- 
geschickte, 1878. 

Back and extremities black, covered with rows of green spots. 
Belly and tail black. Inhabits the Cyclades. 

2. Lac. muralis. var. melisdlensis, Braun : Lacerta lilfordi 
and L. muralis; “Arbeiten aus dem zoolog. zootom. Institut in 
Wurzburg, 1877.” 

Back brown, ornamented with six light longitudinal stripes. 
Belly dark blue, chin rather lighter. Length 130 mm. Inhabits 
the islet Meliseilo near the island of Lissa, in the Adriatic Sea. 

3. L. muralis, var. filflaensis, De Bedriaga : “Die Faraglioni 

Eidechse.” (Heidelberg, 1876.) Braun, v. Bedriaga: 

“ Herpetologische Studien,” in Archiv f Naturg., 1879. 
Gunther : “ Description of a new European Species of Zootoca,” 
Annals and Magazine of Natural History, 1S74. 

Back black covered with small green spesks, the under parts 
are deep blue. Length 212 mm. Inhabits Filfla, near Malta. 

4. L. muralis, var.faragttoniensis, De Bedriaga : “ Ueber die 
Entsteiiung der Farben bei den Eidechsen.” (Jena, 1874.) 
L. muralis var. ccerulma, Elmer: “Zoologische Studien auf 
Capri.” (Leipzig, 1874.) Braun, l.c. 

Back black, the sides blue spotted with black ; the belly a 
brilliant blue. Length 220 mm. Inhabits the Faraglioni Rock, 
near Capri. 

5. L. muralis, var. Latastei, De Bedriaga: “Herpetologische 
Studien,” in Archivf. Naturg., 1879, pp. 264. 

Back and sides brown, or dark brown covered with black 
spots, sometimes with bluish green spots on the sides. Above 
the root of the forelegs a bluish spot. Length 205 min. In¬ 
habits Ponza near Gaeta. 

6. L. muralis, var. Lilfordi, Gunther : “ Description of a New 
European Species of Zootoca,” l.c. Braun, l.c. 

Upper parts of a deep glossy black, lower parts of a beautiful 
sapphire blue. Length 175 mm. Inhabits the Island of Ayre, 
near Minorca. 

7. L. muralis, var. Gigliolii, De Bedriaga : “Herpetologische 
Studien,” 1879, l.c. 

Forepart of the back covered with alternately green and blue 
stripes. The hind part of the back is dark blue. The sides 
are light brown with green and blue spots. The belly brick-red 
with (sometimes without) small blue stripes. Colonring varies. 
Length 175 mm. Inhabits Isla del Dragoneras near Majorca. 

8. A. muralis, var. Rasquineti, De Bedriaga: “Herpeto¬ 
logische Studien,” 1878, l.c. 

Back olive brown with a black pattern. Blue eye-spots orna¬ 
ment the sides. Belly brick-red. The first longitudinal rows of 
the ventral scales are blue. Length 185 mm. Inhabits the islet 
La Deva near Arnao (Spain), J. VON BEDRIAGA 

Heidelberg, August 28 

Insect Swarms 

This year being remarkable for “insect swarms,” it is im¬ 
portant that all possible information about them should be gained, 

46 I 

so as to satisfactorily account for these phenomena. As to 
Vanessa cardui, which has been abundant throughout the spring 
and summer, it is possible that some of those specimens which 
occurred in the spring were the result of a migration from the 
Continent, but there is no doubt that the specimens which are 
now seen are nearly, if not all, bred in this country from ova de¬ 
posited by the spring specimens, quite sufficient time having 
elapsed for the metamorphosis. With regard to Plusia gamma, 
I am of opinion that all the specimens seen, and they have been 
in profusion here from about August 10 till the present time, 
have been bred in this country. My reason for so believing is 
that the larva: were most abundant in the spring, doing damage 
in gardens to a great extent. Some of these larvae I fed lip, the 
perfect insects emerging at the time P. gamma first appeared in 
abundance. My experience of the swarms of P. gamma is that 
they moved in no particular direction, merely passing in numbers 
from flower to flower, flowers being scarce this year, any 
apparent migration being simply a search for more flowers. In¬ 
stead of putting the cause of these swarms down to “migra¬ 
tion,” endeavours should be made to discover the causes of the 
extraordinary periodical fecundity. It is quite probable, too, 
that next year, P. gamma and V. cardui will be scarce, as is 
frequently the case with Colias edusa and hyale after a year of 
abundance. J. H. A. Jenner 

Lewes, September 13 


I have observed, in several recent numbers of Nature, 
various notices of earthquakes, so frequent as to suggest the 
idea to me (perhaps incorrect) that for several months past they 
have been more numerous than usual. Since my arrival in West 
Java 1 have experienced several severe shocks. On March 28, be¬ 
tween 7 and S P.M., I was startled by a peculiar shivering as I sat in 
my chair. At first I imagined I was seized with a terrible fever¬ 
less ague, but I was soon undeceived by the increased bumping ancl 
the clashing of my bottles, See., and the vehement beseeching of 
Tuhan Allah, and the loud exclamations of the natives of, “ We 
are here ! ” “We are all here!” I learned in a few days that 
several villages lying at the base of the peccant volcano, Gecle, 
had suffered ; in particular the town of Ijandjoer, in which 
numerous houses were destroyed, many bridges broken down, 
the telegraph apparatus entirely thrown out of gear, and six or 
seven persons killed. The ground also opened and emitted 
volumes of smoke, while the Gede itself burst out with extra 
vigour, throwing out, in addition to the usual white steamy vapour, 
large quantities of smoke and ashes, fortunately to no great 
distance. Throughout the 28th and 29th there was a succession 
of shocks. On June 3 I experienced a second earthquake, un- 
duiatory but not very severe ; and again on the 5th, undulatory, 
of considerable duration, and severe enough to thoroughly shake 
the whole house and throw down unfixed objects. These have 
done no damage to life, as far as I have heard, and, beyond, 
some houses being cracked in Batavia, little to property. Since 
the beginning of March there have been numerous shocks, but 
none so violent as those of March 28 and June 5. Immediately 
preceding the shock of June 5 there was a sudden and heavy 
fall of rain, the drops being very large. The direction of the 
wave was from east to west. " Henry O. Forbes 

Kosala, Bantam, July 

Leaping power of Mantis 1 

I CAN state from my own observations of several different 
species, both in Ceylon, South Africa, and Fiji, that the power 
is possessed by many, chiefly in the larval stage, and that the 
distances they can spring from branch to branch are very consi¬ 
derable for the size of the insect. E, L. I.AYARD 

British Consulate, Noumea 


The Outer Satellite of Mars.— The following 
positions of Deimos, the exterior satellite of Mars, are 
deduced from the data published in Prof. Asaph Hall’s 
memoir, in which he determines the elements of the 

1 Nature, vol. xx. p. 595. 

© 1879 Nature Publishing Group