April 27, 1882 | 
NATURE 
601 
of growth of the root, and that the loss of hydrotropism 
1S a consequence of the less vigorous growth in the root ; 
this is practically the same criticism as that which 
Wiesner has applied to our views on geotropism ; namely, 
that the lessened rate of growth caused by the injury to 
the punctum vegetationts interferes with the power of 
geotropic curvature. 
Wiesner has, however, himself observed the fact that the 
Zess turgescent roots are those which seem to exhibit bydro- 
tropism best, and as want of turgescence would certainly 
interfere with normal growth, fully as much as the grease 
on the tips of the roots, Wiesner’s criticism seems to be 
considerably weakened. 
In a notice of the present extent, it would be impossible 
to notice all Wiesner’s experiments and arguments, many 
of which possess much interest. To do so, would require a 
whole volume such as Wiesner has devoted to the subject, 
and to which I must refer those who wish to be better 
acquainted with his views. Finally, I would ask those 
who do so, not to forget to refer to ‘‘ The Power of Move- 
ment in Plants,” for it is only by studying the two books 
together, that an adequate opinion on the questions at 
issue can be formed. FRANCIS DARWIN 
OUR BOOK SHELF 
Catalogue of the Batrachia, Salientia and Ecaudata in 
the Collection of the British Museum. By George 
Albert Boulenger. (London: Printed by Order of the 
Trustees, 1882.) 
THIs volume is a proof of the steady though rapid pro- 
gress which our great Natural History Collection is 
making, and is a token as well that under the present 
keeper of the Zoological Department, the stores of speci- 
mens will be made fully available for scientific reference. 
To the working zoologist there can be no more acceptable 
gift than such carefully compiled catalogues, and by the 
publication of such the collection itself not only indirectly 
but even directly benefits, for an interest is awakened in 
the objects described, and thereby the stream of dona- 
tions begins to flow. The first edition of this Catalogue, 
published in 1858, contained the description of some 283 
species, and the collection consisted of some 1691 speci- 
mens. The present edition contains the description of 
800 species, of which the British Museum possesses 522, 
represented by some 4692 specimens. The first edition, 
by Dr. Gunther, without doubt gave a great impulse to 
the study of the tailless Batrachians, and as a result it is 
now out of date. For the present edition Dr. Giinther has 
been fortunate in securing the services of Mr. Boulenger, 
the assistant naturalist in the Royal Museum of Belgium, 
and exceedingly well has the jatter accomplished his task. 
The classification adopted is based on that of Mr. E. D. 
Cope, somewhat modified, and biologists in general will 
be pleased to know that this classification seems to har- 
monise not only with the natural affinities of the genera, 
but with all that is known of the geographical distribu- 
tion, development, and physiology of the group. The 
only serious objection urged against it is the supposed 
difficulty of ascertaining on the recent specimens the 
osteological characters, without sacrificing one or more 
specimens ; but, as Mr. Boulenger asserts, it requires only 
a moderate skill and two or three clean incisions to reveal 
all the required secrets of the structure of the vertebrze. 
One important feature in this catalogue is that we find 
in it an account of all the known species of the group, so 
that it toa great extent possesses the merit of being a 
monograph, and it thus indicates the species which are 
wanting in the National collection. 
considerable beginning made in the descriptions of the 
larval forms, and sometimes these are figured, the collect- 
ing of these forms we trust may receive a fresh stimulus 
from the publication of this work. 
Mr. Boulenger well merits the confidence with which 
Dr. Ginther writes that “zoologists will thankfully 
acknowledge the industry and ability with which the 
author has performed his difficult task.” 
It only remains to add that this catalogue is illustrated 
with numerous woodcut illustrations, and with thirty litho- 
graphic plates. 
LETTERS TO THE EDITOR 
[The Editor docs not hold himself responsible for opinions expressed 
by his correspondents. Neither can he undertake to retuin, 
or to correspond with the writers of, rejected manuscripts. 
No notice is taken of anonymous communications. 
[The Lditor urgently requests correspondents to keep their letters 
as short as possible, The pressure on his space ts so great 
that it 1s impossible otherwise to ensure the appearance even 
of communications containing interesting and novel facts. | 
On the Conservation of Solar Energy 
WiIrH your permission I should like to offer a few remarks 
upon the interesting paper of Dr. C. William Siemens on the 
‘*Conservation of Solar Energy,”’ published in NaTuRE (vol. 
xxv. p. 440). The main hypothesis upon which that paper is. 
based, that of a fan-like action of the sun, is not improbable ; 
nor are the consequences drawn illogical, if we could reasonably 
imagine space to be oceupied by such condensed molecules as he 
supposes. That space is everywhere occupied Ly matter, there 
is no just reason to doubt. The hypothesis of an ether, specifi- 
cally distinct from matter, is a gratuitous assumption, and one 
of the last surviving relics of eighteenth century science. Unless it 
can be proved that highly disintegrated matter is positively 
incapable of conveying light vibrations, there is no warrant for 
assigning this duty to a distinct form of substance. But that 
matter exists in outer space in the same conditions as in the 
planetary atmospheres is certainly improbable. Its duty as a 
conveyer of radiant vibrations seems to require a far greater 
tensity, and its disintegration is probably extreme. 
If we assume, then, that matter exists throughout the universe, 
here as condensed spheres, there as highly rarefied substance, 
with the atmospheric envelopes of the spheres gradually shading 
off into the excessively rare matter of mid space ; another hypo- 
thesis may be deduced, somewhat different to that offered by Dr. 
Siemens. The views which I desire to present have been already 
published, but they seem worthy of repetition in connection with 
his solar theory. 
On the Nebular hypothesis, the matter of the sun was once 
disseminated through space. Gravitative attraction has, there- 
fore, had a double effect. The greater portion of this matter is 
now drawn together into a contracted mass. The remaining 
portion yet occupies outer space, in a far more rarefied condition 
than the original. But an important consequence attends the 
condensation and rarefaction of gases. ‘This is, that condensed 
gases become heated, rarefied gases cooled, and this without the 
aid of heat exchange with outer material. In the one case a 
portion of the absolute heat of the gas, formerly latent, becomes 
sensible ; in the other a portion of the sensible heat becomes 
latent. If originally the absolute heat contents and the tempe- 
ratures were alike equal, condensation and rarefaction would 
not, of themselves, change the heat contents, but they would 
change the temperatures. In condensation, the latent heat is 
reduced, the sensible heat increased, aid the temperature rises. 
In rarefaction the opposite effect is produced, and the temperature 
falls. 
This consideration applies as well to the problem of the con- 
densation of nebulous as of terrestrial gases. The effect of 
contraction of nebulous gas into a dense sphere, must be a con- 
siderable rise in temperature if there be no diminution of absolute 
heat contents. The effect of rarefaction of the remaining matter 
of space must be a decrease in temperature. Thus if radiant 
cutflow of heat from the sun had been prevented during its con- 
densation, the eventual result must have been that the sun and 
the matter of outer space would have continued equal, mass for 
mass, in absolute heat contents, and yet have become immensely 
There is alsoa very | different in temperature. 
And from this must have come another interesting result, 
