J 
be said to have been abandoned. 
a SEPTEMBER 7, 1916] 
THE KINETIC THEORY REVIVED. 
The Dynamical Theory of Gases. By J. H. Jeans. 
Second edition. Pp. vii+436. (Cambridge: 
_ At the University Press, 1916.) Price 16s. net. 
VP ORE than eleven years have elapsed since 
q the first edition of this work was reviewed 
in Nature (April 27, 1905). Most of the pioneers 
of the attempted rigorous mathematical theory 
have passed away, and the attempt to reconcile 
-Boltzmann’s minimum theorem with the properties 
of an aggregate of perfectly reversible units may 
On the other 
hand, the recently developed quantum hypothesis 
has, to some extent, had the opposite effect of 
leading us to believe that something more than 
_ the equations of reversible dynamics is needed to 
account for the phenomena of Nature. 
Equi- 
partition may be characteristic of molecular 
systems, but the celestial universe shows no ten- 
dency towards Maxwell’s law, and would probably 
refuse to obey it even if started according to this 
distribution. 
__ The plan which Prof. Jeans now adopts in his 
book is probably the best one in the circumstances. 
The kinetic theory cannot be proved mathematic- 
ally, neither can the data determined from a calcu- 
lable mathematical theory be made to serve as more 
than approximations to the results of experiments. 
Thus arises a school of slipshod students of 
physics, who, when they cannot prove a result 
mathematically, state that it “has been shown 
experimentally,” and if they cannot get their ex- 
periments to verify they state that it “may be 
proved” (from theory). This danger is largely 
obviated by the division of the earlier chapters 
into four sections, entitled “Mathematical Theory 
of a Gas in a Steady State,” “ Physical Properties 
of a Gas in a Steady State,” ‘Mathematical 
Theory of a Gas not in a Steady State,” “ Physical 
Phenomena of a Gas not in a Steady State.” 
Among the miscellaneous applications it is 
interesting to note Prof. Jeans’s remarks on the 
rate of escape of gases from planetary atmo- 
spheres. It will be remembered that the late Dr. 
Johnstone Stoney attempted to account for the 
loss of gases by the motion of the molecules which 
describe hyperbolic orbits under the attraction of 
the primary; and by assuming the absence of a 
particular gas from a particular member of the 
system he deduced the absence of other gases from 
other systems. It was, however, subsequently 
shown that, under the assumptions made by Dr. 
Stoney, the gases in question would not escape, 
and Dr. Stoney advanced the opinion that the 
methods of the kinetic theory on which his own 
investigations were based were inapplicable to the 
problem to which he had applied them. Accord- 
ine to Prof. Jeans’s views, hydrogen does not at 
present escape, but it did so when the earth was 
at a far higher temperature than at present. On 
the other hand, the brief discussion on our exist- 
ing knowledge regarding the upper and lower 
tegions of the atmosphere will help to reconcile 
theory with experiment. 
NO. 2445, VOL. 98] 
NATURE 
ere Rs A Oa ea ce 
eee 
3 
The book thus contains as much information 
as an ordinary physics honours student can profit-. 
ably study. But, of course, this is nothing like 
the whole of the kinetic theory, whether studied 
mathematically or experimentaily. 
MENDELISM ON THE FARM. 
A Manual of Mendelism. 
Pp. 152. (London: A. 
1916.) Price 2s. 6d. net 
pane WILSON has prepared an exposition 
of Mendelism which will be of special interest 
to stock-breeders and serious students of agricul- 
ture. It is a model of clearness and directness, 
and bears the marks of the teacher as well as of 
the investigator. After explaining Mendel’s ex- 
periments, his rule and his theory, the author 
passes to a discussion of various disturbing 
causes which account for abnormal distributions 
of characters. Thus there are cases in which the 
effects of the individual factors cannot be iden- 
tified separately; cases of the suppression of the 
effect of one factor by that of another; cases of 
incomplete or absent dominance; cases where a 
factor is believed to combine indifferently with 
more than one other; cases where two or more 
factors seem to be linked together so that they are 
handed on from generation to generation as one; 
and cases in which two different factors produce 
a similar effect. 
These are some of the reasons for results which 
are not typically Mendelian, and they might have 
been added to. Thus it has been convincingly 
shown by Morgan and others that environmental 
and developmental influences may have a profound 
effect on the outcome of Mendelian factor-differ- 
ences. Prof. Wilson goes on to illustrate the im- 
provements which have rewarded careful experi- 
mentation, e.g. as regards yield of wheat and of 
milk. That Mendelian formule can be used 
towards an increased production of material 
wealth has been proved by the results of workers 
like Nilsson-Ehle and Pearl, and these are but 
indications of what might be achieved. The aver- 
age yield of wheat in Britain is about 32 bushels 
to the acre; it might be raised to go or even 50 
bushels. ‘For every day by which the life of a 
variety of wheat is shortened between seed-time 
and harvest, the wheat-growing area in Canada 
reaches fifty or sixty miles farther northwards.” 
The work done in Denmark shows how the 
wealth of Britain, so far as it proceeds from dairy 
cattle, might be very nearly doubled. Those who 
wish to know how such exceedingly desirable 
results can be attained will be well advised if they 
study a book like Prof. Wilson’s. It will show 
them how they may act with circumspection and 
foresight. The book would have been the better 
for pictures and its terse style is perhaps a trifle 
severe, but it is a book for the times, competently 
and carefully executed, which those whom it espe- 
cially concerns should.run to read. 
By Prof. James Wilson. 
and. C. Black, Ltd., 
