the statements made in the correspondents’ replies. But 
we think that it will be admitted that as a whole those 
replies are eminently satisfactory. 
A circumstance quite noteworthy, however, strikes the 
reader who scrutinises the lists as tabulated recording the 
instances of zujred, and we would be glad to hear some 
explanation or interpretation of what at present seems 
inexplicable. Thus out of the first six races only three 
men are recorded as injured, while out of the next four 
races nine men are so recorded, five being mentioned in 
one race—that of 1845—and two more in the race 
of the following year. Again occurs a period of compara- 
tive immunity from injury, only one case being instanced 
in the next seven races. Once more is the order changed, 
for in the following four races four men are recorded as 
injured, while in the five remaining races of the series no 
injury whatever seems to have been sustained. The author 
does not seem to have instituted any inquiry on this 
point, yet surely it is one worth investigation, seeing that 
it is this very matter of liability to injury which is the 
sole subject of dispute, to settle which is the avowed 
object of his book. Was this injury-rate affected by the 
mode of training of the crews, the physical calibre or 
age of the individual men composing them, by the seve- 
rity of the contest itself, or by the character of the season 
when the men trained and rowed? J 
ARCHIBALD MACLAREN 
THOMSON & TAIT’S NATURAL PHILOSOPHY 
Elements of Natural Philosophy. By Professors Sir W. 
Thomson and P. G. Tait. Clarendon Press Series. 
(Macmillan and Co., 1873.) 
PeU RAL Philosophy, which is the good old 
English name for what is now called Physical 
Science, has been long taught in two very different ways. 
One method is to begin by giving the student a thorough 
training in pure mathematics, so that when dynamical re- 
lations are afterwards presented to him in the form of 
mathematical equations, he at once appreciates the lan- 
guage, if not the ideas, of the new subject. The progress 
of science, according to this method, consists in bringing 
the different branches of science in succession under the 
power of the calculus. When this has been done for 
any particular science, it becomes in the estimation of the 
mathematician like an Alpine peak which has been scaled, 
retaining little to reward original explorers, though per- 
haps still of some use, as furnishing occupation to profes- 
sional guides. ; 
The other method of diffusing physical science is to 
render the senses familiar with physical phenomena, and 
the ear with the language of science, till the student be- 
comes at length able both to perform and to describe ex- 
periments of his own. The investigator of this type is in 
no danger of having no more worlds to conquer, for he 
can always go back to his former measurements, and 
carry them forward to another place of decimals. 
Each of these types of men of science is of service in 
the great work of subduing the earth to our use, but 
neither of them can fully accomplish the still greater 
work of strengthening their reason and developing new 
powers of thought. The pure mathematician endeavours 
to transfer the actual effort of thought from the natural 
NATURE 
399 
= ee 
phenomena to the symbols of his equations, and the 
pure experimentalist is apt to spend so much of his 
mental energy on matters of detail and calculation, that 
he has hardly any left for the higher forms of thought. 
Both of them are allowing themselves to acquire an un- 
fruitful familiarity with the facts of nature, without taking 
advantage of the opportunity of awakening those powers 
of thought which each fresh revelation of nature is fitted 
to call forth. 
There is, however, a third method of cultivating physical 
science, in which each department in turn is regarded, 
not merely as a collection of facts to be co-ordinated by 
means of the formulz laid up in store by the pure mathe- 
maticians, but as itself a new mathesis by which new ideas 
may be developed. 
Every science must have its fundamental ideas—modes 
of thought by which the process of our minds is brought 
into the most complete’ harmony with the process of na- 
ture—and these ideas have not attained their most perfect 
form as long as they are clothed with the imagery, not of 
the phenomena of the science itself, but of the machinery 
with which mathematicians have been accustomed to 
work problems about pure quantities. 
Poinsot has pointed out several of his dynamical inves- 
tigations as instances of the advantage of keeping before 
the mind the things themselves rather than arbitrary 
symbols of them ; and the mastery which Gauss displayed 
over every subject which he handled is, as he said himself, 
due to the fact that he never allowed himself to make a 
single step, without forming a distinct idea of the result of 
that step. 
The book before us shows that the Professors of Natural 
Philosophy at Glasgow and Edinburgh have adopted this 
third method of diffusing physical science. It appears from 
their preface that it has been since 1863 a text-book in 
their classes, and that it is designed for use in schools and 
in the junior classes in Universities. The book is there- 
fore primarily intended for studeats whose mathematical. 
training has not been carried beyond the most elementary 
stage, 
The matter of the book however bears but small re- 
semblance to that of the treatises usually put into the 
hands of such students. We are very soon introduced to 
the combination of harmonic motions, toirratational strains, 
to Hamilton’s characteristic function, &c., and in every 
case the reasoning is conducted by means of dynamical 
ideas, and not by making use of the analysis of pure 
quantity. 
The student, if he has the opportunity of continuing 
his mathematical studies, may do so with greater relish 
when he is able to see in the mathematical equations 
the symbols of ideas which have been already presented 
to his mind in the more vivid colouring of dynamical 
phenomena. The differential calculus, for example, is at 
once recognised as the method of reasoning applicable to 
quantities in a state of continuous change. This is 
Newton’s conception of Fluxions, and all attempts to 
banish the ideas of time and motion from the mind must 
fail, since continuity cannot be conceived by us except 
by following in imagination the course of a point which 
continues to exist while it moves in space. 
The arrangement of the book differs from that which 
has hitherto been adopted in text-books, It has been 
