340 
INERT E 
[AuGusT 10, 1899 
and that a book which enters into questions of entropy 
and thermodynamic relations might pass a little more 
rapidly over baby mechanics. This remark applies 
specially to the illustrations, some of which are of the 
most elementary character and even childish. 
This brings me to the second point I wish to submit 
to the consideration of authors. A number of illus- 
trations in modern books seem to me to be put in for the 
sake of interrupting the text by a picture rather than for 
the sake of explanation. There is, for instance, the 
usual illustration which pretends to illustrate the fact 
that all bodies fall in vacuo with the same velocity. A 
long glass tube with a tap at the lower end, two hands 
holding it, and about a third of the way downward a 
small black dot and another dot a little bigger about a 
millimetre higher up. I suppose that the dots represent 
bodies, and that their closeness is intended to show their 
falling together. Unfortunately, in the present instance 
the stopcock at the bottom is open according to English 
ideas (though closed if they mean to be French taps), so 
that the intelligent student unacquainted with the habits 
of the French plumber would carry away the idea that 
bodies fall together in air at atmospheric pressure. But 
without laying stress on this, I should like to know the 
opinion of my colleagues, whether they seriously believe 
that students are assisted by illustrations of this nature. 
Some psychological freak may account for its being so ; 
but it seems odd to me, and is worth investigating. I 
have marked several other instances of illustrations 
which seem to me to be of the same type. On the other 
hand, the diagrams illustrating graphic methods in 
thermodynamics are clear and well chosen. 
Finally, I am not quite sure I like the introduction of 
exercises and examples. Examinations, no doubt, are a 
necessity, and I have no objection to books written 
specially to push boys through them, but the present 
book is too good to serve in this manner, and one 
does not quite like being constantly reminded of the 
fact that ninety-nine per cent. of students only study 
physics because they are obliged to do so, and I have 
never yet seen a student, or seen any one to my 
knowledge who knows a student, who will work through 
an example without the stimulus of examinations upon 
him. I should prefer to see the examples collected in a 
special appendix at the end. Two small points I may 
draw attention to, as the author may wish to correct 
them in another edition. Speaking of solar heat, Lord 
Kelvin’s theory of falling meteorites is mentioned, but 
nothing is said about the now generally accepted theory 
of Helmholtz that the sun’s contraction by his own gravi- 
tation is sufficient to account for the keeping up of his 
temperature. 
Speaking of the fact that the surface of liquid at rest is 
a horizontal plane, the author considers it in § 127 to be a 
sufficient proof that the image of a plumb line is observed 
to be a prolongation of the line itself, for it is said that 
“an object and its image are symmetrical only when 
the reflecting surface is plain.” Will not a spherical 
surface do equally well, if the plumb line passes 
through the centre of the sphere? If I add that in the 
figure on p. 108 the meniscus of a mercury column is 
wrongly drawn, inasmuch as its curvature diminishes as 
it approaches the glass sides, I have exhausted all the 
NO. 1554, VOL. 60] 
blemishes which the critical mind can discover. But I 
started to praise rather than to criticise, and must conclude 
with the hope that the volumes on light and electricity 
will soon be ready for publication. 
ARTHUR SCHUSTER. 
OUR BOOK SHELF. 
The Tides Simply Explained: with Practical Hints to 
Mariners. By the Rev. J. H. S. Moxly, B.A., T.C.D:, 
Chaplain to the Forces ; Chaplain to Chelsea Hospital. 
Pp. vili + 151. (London: Rivingtons, 1899.) 
THIS is a paradoxical work which may do harm owing 
to the standing of its author. He openly avows himself 
at war with the scientific world :— 
“What is this strange hallucination that has taken 
possession of the minds of great mathematicians? I have 
quoted several truly absurd statements and arguments of 
our teachers in my first chapter. I wished to show my 
readers, by many infallible proofs, that the idols of 
authority, to which we have been bowing down, are not 
the correct thinkers we have supposed them to be” 
(p. 58). 
rie could not be much more severe if scientific men 
were a general-staff. His method of “infallible proof” 
of the fallibility of these idols is simple ; he quotes a 
sentence or a paragraph, and then says : 
“ This is, of course, sheer nonsense! It is too absurd 
a statement to deserve any answer” (p. 8). 
Having disposed of existing theories by this drastic 
process, he proceeds to give his own theory of the 
tides : 
“The moon and earth are being drawn together by the 
attraction of gravity, yet they do not come together. 
There must therefore be a force equivalent to the force 
of attraction, but acting in an exactly opposite direction, 
which keeps the earth and moon asunder. It does not 
matter what we call it! ‘Centrifugal force’ will do fora 
name for it, if you like. The point for us is that the force 
does exist—must exist, and that it is exactly equal to the 
attractive force, but opposite in direction. Wed/, then, i7 
the attractive force ratses a tide under the moon, the force 
opposite the attractive force will produce a similar effect 
on the opposite side of the world” (p. 52). 
The sentence in italics (which are mine) is one of the 
neatest things in paradox I have come across. It is 
scarcely surprising that the man who could invent it 
should be able to deduce from this amazing premiss the 
correct expressions for the tide-generating force at any 
point on the earth’s surface. But then he throws this 
advantage to the winds, by despising the horizontal com- 
ponent as insignificant, and electing to work with the 
vertical component only, because it suggests to him an 
attractive but hopelessly false analogy. We are to 
imagine a gigantic power taking the world in its grasp, 
as a schoolboy would squeeze a ball between his finger 
and thumb. The horizontal component of tide-generating 
force is compared to a butterfly harnessed to Nelson’s 
Column ; but, to suit his own ideas as regards vertical 
force, Mr. Moxly makes the butterfly a schoolboy and 
Nelson’s Column an india-rubber ball. 
After stating this general theory, Mr. Moxly examines 
some cases of what have been unfortunately called 
“ abnormal” tides, and triumphantly gives explanations 
of them ; partly wrong, and partly such as any one could 
deduce from a general knowledge of the locality ; and, as 
this is done with some skill, it is to be feared the book 
may mislead some of the “mariners” to whom it is ad- 
dressed. It is to be hoped that before trusting Mr. 
Moxly they will wait until he has produced detailed and 
successful tide-tables for any given port deduced fairly 
from his own theories. JeG slat, lle 
——S ss 
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eR ant eee ert alltel 
———s 
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