Pye SF 
ae a. 
June 30, 1923] 
NATURE 
873 

and men of science, he expresses himself clearly, so that 
any one who reads his book will discover at least one 
philosopher who does not “ tell us what every one knows 
in language that no one can understand.” 
Part 1 consists of an analysis of the conceptions of 
space and time in modern physics and leads up to an 
account of the special and general theories of relativity. 
This has all been done before, but not quite in the same 
way. The author starts at the beginning, or what 
ought to be the beginning of any such discussion, by 
giving a simple account of Prof. A. N. Whitehead’s 
“Principle of Extensive Abstraction.” This. prin- 
ciple provides a rational method of passing from the 
actual facts of sense-experience to the highly sophisti- 
cated conceptions, such as points and lines, that are 
necessary for geometry and mathematical physics, and 
is indispensable for any proper theory of space and time. 
Prof. Broad’s exposition provides a good introduction 
to Prof. Whitehead’s own decidedly difficult works. In 
the second chapter on time and change, with Prof. 
Whitehead’s treatment of time as a basis, some valu- 
able and original ideas are developed. This chapter 
is perhaps the most important in the whole book. The 
rest of Part 1 follows well-established lines and does not 
call for special comment, except in so far as it gives a 
clear account of a difficult subject. 
In Part 2 the author takes up his problem from a 
different point of view, that of the relation of the 
physical theory of material bodies to the facts of sense- 
experience. Here Prof. Broad is for the most part 
breaking new ground, and for that reason alone his 
argument is rather more difficult to follow. More- 
over, he is now dealing with problems which do not 
appeal greatly to the man of science, who may refuse 
to recognise them as problems at all. He will probably 
assent vaguely to the saying of Petronius standing at 
the head of chapter 7 : 
Fallunt nos oculi, vagique sensus 
Oppressa ratione mentiuntur. 
The man of science may even confess that the 
ridiculous theory of pp. 272 and 273 is not an unfair 
summary of his own and his friends’ views as to the 
nature of physical objects and their sensible appear- 
ances, but still he may be inclined to say, “‘ Why make 
all this fuss about it? I know it is easy for a philo- 
sopher, with his puzzles about pennies that are ‘ really’ 
round, though they ‘look’ elliptical, and about mirror 
images, and so on, to pick holes in the ordinary common- 
sense and scientific notion of material objects, but what 
does it all come to? The ordinary theory, however 
silly ultimately, is simple and familiar and works well 
in practice. The philosophical theories are not simple, 
there are several different ones, and there is nothing to 
-show that they are better for ordinary purposes.” 
NO. 2800, VOL. 111] 
- ever comfortable. 
Prof. Broad has not played his cards very well in 
order to refute such contentions as this and induce the 
man of science to read on, for he has kept his best 
arguments for his last chapter. The argument is, 
briefly, that the ordinary view only works in practice 
by leaving out the facts that do not fit in with it. It 
so happens that these inconvenient facts have not, up 
to the present time, been important and that the man 
of science has been well advised to forget them and get 
‘on with his work, but this happy state of affairs may 
not last for ever. The history of the theory of space 
and time supplies the moral. The traditional theory 
was simple and easy to understand and worked well ; 
the engineer and the chemist still ask for nothing 
better. It has only been gradually that the incom- 
patible facts have been forced on people’s attention in 
spite of struggles to ignore them; and some people 
still ask, “‘ Why all this fuss about the principle of 
relativity ?”’? The only answer is that clear ideas, if 
we can get them, are better than muddled ones, how- 
What is worth doing for space and 
time is also worth attempting for sense perception and 
material objects. 
It is impossible in the course of a short notice to 
make any detailed criticisms of this latter part of the 
book ; suffice to say it is the kind of thing scientific 
philosophers ought to write and philosophical men of 
science to read. 
The author shows wit and erudition in his chapter 
headings, though he might have translated King Alfred 
forus. The index is full and carefully compiled. As the 
author shows some pedantry in the matter of authors’ 
names and titles, it is not unfair to point out that 
Galileo is a Christian name, consequently there was no 
such person as “ Galileo, G.” A.D. R. 
Geology in War. 
(1) The Work of the Royal Engineers in the European 
War, 2974-19. Workin the Field under the Engineer- 
in-Chief, B.E.F. Geological Work on the Western 
Front. Pp. 71+7 plates+19 figs. (Chatham: W. 
and J. Mackay and Co., Ltd., 1922.) 
(2) The Work of the Royal Engineers in the European 
War, 1974-19. Workin the Field in other Theatres 
of War. Egypt and Palestine—Water Supply. Pp. 
vi+64+7 maps+1o plates. (Chatham: W. and J. 
Mackay and Co., Ltd., 1921.) 
N 1914 there was no geological organisation in the 
| British Army, though it would appear that the 
Germans had a definite geological establishment in 
connexion with each of their Armies. Very early 
during the War the need of geological advice was 
felt in connexion with the supply of water to the 
2CclI 
