318 
NATURE 
[JANUARY 31, 1907 
and if he only received eleven replies it cannot be 
denied that the writers of these replies fairly repre- 
sented all sorts and conditions of men, and that the 
subject has been discussed, (1) in its academic aspect, 
(2) from the point of view of the experienced school- 
master, and (3) from the standpoint of the engineer. 
The book contains a reprint of the recommendations 
of the Committee of the Mathematical Association on 
the Teaching of Elementary Mechanics. 
What conclusions can the average reader infer from 
the divergent opinions expressed in this boolx? 
(1) There is a general consensus of opinion that 
the teaching of mechanics should be more experi- 
mental and less dogmatic. 
(2) Prof. Perry condemns the use of costly and 
complicated laboratory apparatus, and considers that 
more can be learnt from a cheap screw jack and a 
rusty old pulley than from costly Atwood’s machines. 
In this he is perfectly right. 
(3) If the teaching of mechanics is to be made more 
practical, greater attention should be paid to friction 
and other resistances which occur in nature. So long 
as friction is shelved into the background, mechanics 
cannot be anything but the study of what would 
happen under impossible conditions. 
(4) The advocates of the poundal and the advocates 
of the slug will never agree. 
(s) The academic side does not wish the poundal 
adopted for practical purposes (p. 13). In examina- 
tion papers answers are never—well hardly ever— 
asked for in poundals, and generally a candidate 
would lose marks by giving the pull of a railway 
engine in poundals or tonals. But the academic 
teacher strongly objects to swallowing the slug, and 
not without reason. 
(6) The engineering side is trying hard to force 
the slug down the throat of the academic teacher, 
its main plan of campaign consisting in attacking 
the poundal as unit of force. 
(7) Both sides seem willing, up to a certain point, 
to allow beginners to solve elementary problems by 
the use of Newton’s laws, according to which change 
of motion is proportional—not equal to the impressed 
force—a method which avoids both the poundal and 
the slug. But they still cling tenaciously to the 
modern substitute for Newton’s statements. 
(8) The engineering side has had to accept the 
C.G.S. dynamical units, and there seems no reason 
why schoolboys should not leave the equation F=ma 
until they learn to worl* with the metric system. 
(9) The universal adoption of the metric system 
affords the most probable direction for a compromise. 
(10) Prof. Perry advocates (p. 61) teaching 
mechanics through force rather than through mass 
as the fundamental notion; and yet some remarks 
seem rather to indicate that he wishes every school- 
boy to realise that force is the vector time flux of 
momentum. 
(11) Many teachers condemn tonals, velos and celos, 
others strongly advocate them. One critic (p. 55) 
goes so far as to express regret ‘‘ that for units of 
momentum and mass-acceleration we have no suitable 
NO. 1944, VOL. 75] 
names at all’?; but does not the poundal meet his 
requirements when regarded as’ the unit of mass- 
acceleration? Surely it is the use of this unit for 
measuring forces (by naval engineers and others) that 
is open to the serious objections raised on p. 64. 
(12) The same differences exist in regard to centri- 
fugal force. 
We have no wish to reopen controversies on these 
questions, but we cannot help thinking that if every 
schoolboy is to know the laws of motion, it is also 
important that every schoolboy should know a great 
deal about the laws of the country he lives in. He 
should also learn something about economics, some- 
thing about choice and chance, in order that he may 
not develop into a gambler, some experimental and 
geometrical optics, and many other things besides, 
which he does not now learn. That ‘‘it must be 
good for all boys to learn something of measurement 
and how to use their hands ”’ is a point on which all 
can agree with Prof. Perry. G: HeaB: 
OUR BOOK SHELF. 
What Are We? By Leonard Joseph. Pp. xiii+394. 
(London: Kegan Paul, Trench, Triibner and Co., 
Ltd.; 1906.) Price 15s. net 
“THEY say the owl was a baker’s daughter. Lord, 
we know what we are, but know not what we may 
be.”? A certain incoherence in Ophelia’s words would 
have prevented us at one time from regarding her 
as a possible authority on the metaphysical questions 
raised by the title to this book, but she is soundness, 
suggestiveness, and lucidity themselves when com- 
pared with Mr. Joseph. 
Three peculiarities in this pretentious work will 
strike the observant reader:—(1) Excellent as 
‘“Chambers’s Encyclopedia’? and the paper called 
Answers are in their own place—and Prof, York 
Powell is said to have thought highly of the latter— 
we doubt if there are many scientific works of the 
first rank in this country in which these are paraded 
in the foot-notes or in the list of books consulted. 
(2) Mr. Joseph poses in the opening paragraphs as an 
orthodox believer whose motto is *‘ Search the Serip- 
tures, watch and pray,’’ but confesses in the end, 
with much pride, that this is merely a device to 
secure for his pages a reading from unreasonable and 
stubborn church-goers. It would have been more 
tactful to assume that all his readers were reason- 
able human beings, or that, at any rate, the weight 
of the arguments adduced would of itself overcome 
all initial distrust. (3) Mr. Joseph argues soberly— 
if the term sober can be applied without contempt to - 
one who apparently abhors total abstainers as amongst 
the most depraved of men—for sexual promiscuity. 
This is bad; indeed, it is even worse than the un- 
sound physiology that defaces the last page, or than 
the wealth of padding which surrounds and encom- 
passes what might have received adequate treatment 
in a sixpenny pamphlet. 
The Human Mechanism, its Physiology and Hygiene 
and the Sanitation of its Surroundings. By Prof. 
Theodore Hough and Prof. W. T. Sedgwick. Pp. 
ix+564. (Boston and London: Ginn and Co., 
1906.) Price 8s. 6d. 
Many writers of text-books on physiology for the lay 
public are quite incompetent to act as teachers of their 
fellow men, because they are unacquainted with the 
