698 

Carr adds a new edition of his valuable book, which he 
has extended by a new chapter giving a more detailed 
description of Einstein’s theory. Then there is a group 
of bare expositions of Einstein’s theory, following closely 
his published work, with little digression or reflection. 
To this class belong the works of Drs. Silberstein and 
Kopff, which are mainly a record of lectures given by 
the authors in Toronto and Heidelberg respectively. 
Einstein’s own volume, entitled “The Meaning of 
Relativity,” is disappointing, as it falls straight into 
the same group, and gives us little more light on the 
meaning of relativity, save a re-emphasis that it is 
mainly a matter of mathematics. Prof. Murnaghan 
in his volume is more specially concerned with the 
pure mathematics, and seeks to lessen the difficulties 
of ‘*The Absolute Differential Calculus” in any 
number of dimensions by tracing the whole subject 
through in an elementary manner. Prof. Drumaux 
writes a bright, readable, and well-balanced account 
of the theory ; his genera! conclusions are admirable. 
But the latest works of Profs. Eddington and White- 
head have characters of their own. We are exceed- 
ingly glad to have kept Prof. Whitehead’s book 
by us until we have had an opportunity of seeing in 
book form the matured results of Prof. Eddington’s 
mathematical investigations and his speculations as to 
the interpretation to be placed upon it all. We should 
recommend all those who are puzzled by the higher 
flights of his imagination to sit down to Prof. White- 
head’s book, and after worrying through his first four 
chapters on physical principles to come back to Prof. 
Eddington and reconsider what he has to say. For 
while we yield to no one in our admiration for the 
work which the latter has done in emphasising the 
necessity for a thorough revision of the basic ideas of 
physical science, there remains an obstinate feeling 
that some of the more fascinating glimpses which he 
gives us may not stand a thorough logical examination. 
Prof. Whitehead, on the other hand, is a conservative. 
He acknowledges and presupposes the magnificent 
stroke of genius by which Einstein and Minkowski 
assimilated time and space, but, as he says, “ The 
worst homage we can pay to genius is to accept un- 
critically formulations of truths which we owe to it.”’ 
Accordingly, the major part of his book is devoted 
to a logical consideration of the spatio-temporal 
character of events. Chapter II. consists of a lecture 
on “ The Relatedness of Nature,” given to the Royal 
Society of Edinburgh. It emphasises the fact that in 
our contemplation of Nature we are regarding events 
and processes. Descartes considered “stuff” (matter, 
ether) as being separable from the concept of process, 
realising itself at an instant, without duration ; and 
“extension” was an abstract from the more 
NO. 2795, VOL. 111] 
to him 
NATURE 

[May 26, 1923 

concrete concept of “stuff.” Space is thus essentially 
dissociated from time. But if, as Prof. Whitehead does, 
we find in events the ultimate repositories of the varied 
individualities in Nature, then we obtain the four-dimen- 
sional space-time as an abstra€t from those events. 
Space and time are thus correlative abstractions which 
can be made in different ways, each way representing 
a real property of Nature. The “event” or “ point- 
event” which is made fundamental by many writers — 
is therefore a pure abstraction, a fundamental element 
in the deductive and synthetic conceptual model which 
we have formed of Nature, holding the same place in 
it as the “ point ” in Euclid’s elements of geometry. 
So far we should find complete agreement between 
Einstein, Minkowski, Eddington, and Whitehead. It 
is when we come to the next chapter that we begin to 
feel that new ground is being broken, for Prof. White- 
head has perceived that the careful scrutiny of funda- 
mental ideas necessitated by this unification of space 
and time has not yet been thoroughly carried out. 
The whole question of the nature of measurement and 
how it is at all possible has to be tackled, and we must 
begin by analysing the notion of “ equality.” In 
accordance with the ideas above, the fundamental 
step must be the matching, not of permanent bodies, 
but of passing events. “‘ How time is to be got from the 
relations of permanent bodies completely puzzles me.” 
“Why this pathetic trust in the yard measure and the 
clock?” he exclaims. So, starting from the simple 
idea of equality, we are led on into all those speculations 
concerning the character of the universe which have 
; been raised by Einstein’s theory. 
We are left at the end of this chapter with a sense 
that “ equality ” and ‘‘ measurement,” far from being 
the sure foundation of physics, are either crude and 
primitive modes of experimentation or else the finishing 
touches to a wonderfully wrought conceptual picture of 
Nature. Here we think Prof. Whitehead and Prof. 
Eddington will be in sharp disagreement, and here we 
think remains still much room for clear exposition and 
hard thinking. While we welcome Prof. Eddington’s 
authoritative exposition of the mathematical theory 
of relativity, our doubts as to the logic of his fascinat- 
ing general account of the theory are confirmed. 
In the first section the fundamental hypothesis is 
stated that “ everything we can know about a con- 
figuration of events is contained in a relation of ex- 
tension between pairs of events. This relation is 
called the interval.” The equality of intervals is to 
be tested observationally. We are told to take a 
configuration of events, namely, a measuring-scale, and 
lay it over a distance AB, and observe that A and B 
coincide with two particular events P, Q (scale-divi- 
sions). It seems to us that a scale-division is not an 
