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NATURE 

"marshalling of the genera according to the number of 
their species is not merely that the percentage of 
_ monotypes is largest on islands (as might be expected), 
but that it is exceptionally high in S. America and in 
_ Africa. The corresponding curves from several other 
regions are altogether different. I do not wholly 
_ follow the argument by which these features of regu- 
_ larity are interpreted as giving strong support for the 
ve _ theory of Age and Area. Whatever be the meaning ° 
of the regularity of the curve of frequency of species 
- distributed according to genera, the occurrence of 
: order in this unexpected place does not readily accord 
with the Darwinian view that specific’ diversity” is 
primarily or closely dependent on fitness. That 
deduction, which looked so attractive in the super- 
ficial survey which was all that could be undertaken 
in Darwin’s time, became practically untenable so 
soon as the phenomena of variation were accurately 
explored, and it is not surprising that close investiga- 
tion of another part of the species-problem has revealed 
_a similar weakness. 
_ On the other hand, though the point is a minor one, 
the considerations collected under the title “ Size and 
_ Space,” though adduced as fatal to the theory of 
_ Natural Selection seem to have little cogency. On 
he average, genera with more species are shown to 
_ extend over greater space, and hence the area occupied 
tee a genus corresponds roughly with the number of 
species it contains. What else could we expect? A 
7 i = college, with a larger and more varied supply of 
competitors, commonly shows more successes (and 
_ indeed more failures) in more varied departments of 
_ activity than will be achieved by a smaller establish- 
aed 
~ One excellent purpose Dr. Willis’s book will certainly 
serve. It will renew the debate on the mode of 
_ evolution, which for many reasons has of late years 
languished. Whatever doubts arise regarding the new 
deductions, Dr. Willis once more makes geographical 
distribution a live study, showing quite unexpected 
_ lines along which it may be pursued. The delimitation 
_ of floral areas—or, for that matter, zoological areas too 
—was, as he says, a dull and almost futile exercise of 
 scholasticism. The introduction of statistical methods, 
here altogether appropriate, offers great possibilities. 
In stronger hands a still greater effect might have 
been produced. The style of presentation scarcely 
attains the level required of such works by an age not 
_ Over-exacting in that respect. Finish is no longer 
demanded of scientific authors, and we have come to 
_ suppose that loose writing is compatible with clear 
thinking. None the less it makes very difficult reading. 
‘3 Those who are not alienated by such blemishes will 
_ find the book interesting as a challenge. 
NO. 2776, VOL. 111] 
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How far 
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ef 
the new ideas are of value and how many of them are 
fallacious we shall scarcely know till they have been 
tried in practice over wide fields of experience, and 
examined in perspective from many aspects. 
W. Bateson. 
The Internal Combustion Engine. 
The Internal-Combustion Engine. By Harry R. 
Ricardo. Vol. 1: Slow-speed Engines. Pp. vii+ 
488. (London and Glasgow: Blackie and Son, 
Ltd., 1922.) 30s. net. 
N R. RICARDO has completed the first volume of 
his promised book on the internal combustion 
engine,and according to the preface ‘hopes shortly to be 
able to complete the second.”’ Seeing that the present 
volume deals entirely with the slow-speed engine, and 
was for the most part written many years ago, it is to 
the volume to come, dealing with the modern high-speed 
engine and embodying the results of recent researches, 
that the readers of Nature will turn with greater 
interest. Mr. Ricardo is giving us two books rather 
than two volumes of one book, and it is a pity there- 
fore that the volume now completed is not provided 
with an index. 
The development of the internal combustion engine 
coming so much later than the steam engine, it was 
natural that during infancy its progenitors should be 
more disposed to seek the aid of physics and chemistry 
as god-parents than had been those of its rival, the steam 
engine, which received this baptism only in riper years. 
It is refreshing to a student of science to see how— 
and in Mr. Ricardo’s contributions in particular—the 
limits of internal combustion engine design are studied 
in the light of modern knowledge of the detonation 
of compressed gases, flame temperature and flame 
velocity, the effect of change of specific heat, the effect 
of mass on dissociation. The results are very striking. 
The investigator of a new problem, instead of groping 
for a solution in the dense thicket of possibilities, is able, 
by using the laws of physics and chemistry as guides, 
to mark off the possible from the impossible, and so to 
reduce the area to be cleared to very much smaller 
dimensions. One catches the process at work in the 
volume before us, but for the culmination of its pro- 
ductiveness one has to wait for the stimulus of the war 
period with its impetuous demand for new engines 
for more and more effective flight. The impetuosity 
of this demand is illustrated by M. Rateau’s recent 
paper at the Institution of Mechanical Engineers : two 
long-unsolved problems of the internal combustion 
engine are the compounded engine and the gas turbine : 
the needs of aviation are shown by M. Rateau insistently 
to demand some sort of solution of both these problems 
