NATURE 
[DECEMBER 17, 1903 
well to issue separately the chapter on graphs from 
their recent text-book of elementary geometry. The 
subject is well introduced, and the young readers are 
led on by easy stages and well selected examples. In 
connection with the plotting of sines, cosines and tan- 
gents, a short table of these functions, from which the 
pupils could take out their own values, would have 
been very instructive if it could have been provided. 
It seems a pity that no mention is anywhere made of 
the slope of a curve; comparatively few persons have 
yet recognised that the practice of graphing affords 
a valuable opportunity of helping to put into more 
tangible shape the idea of a rate which is certainly 
possessed in a greater or less degree even by the very 
young. 
A CAMBRIDGE TEXT-BOOK OF PHYSICS: 
Electricity and Magnetism. By R. T. Glazebrook, 
M.A., F.R.S. Pp. viiit44o0; diagrams. (Cam- 
bridge: University Press, 1903.) Price 7s. 6d. 
HE present work represents a first-year course of 
Dr. Glazebrook’s lectures in electricity and 
magnetism when at Cambridge. It forms one member 
of a series of which ‘‘ Mechanics,’’ ‘‘ Heat,’’? and 
“Light? have already appeared. The issue of these 
manuals was undertaken in response to a request that 
his lectures might be printed for the use, primarily, of 
the students attending the practical classes at Cam- 
bridge. Thus Dr. Glazebrook rather apologetically 
explains the publication of another book dealing with 
elementary electricity. 
It is true that the number of elementary text-books 
is legion, and a man may well hesitate before adding 
to their number. Yet we think that there is still 
room, and that if a book of superlative value appears 
it will not fail to find a welcome. 
In attempting to estimate whether the present 
volume is a noteworthy addition to elementary liter- 
ature, let us in the first place say that it has un- 
doubtedly many excellences. The method followed 
throughout is that with which we are already familiar 
in the other members of the series. 
This method consists in mingling the theoretic and 
experimental sides of the subject, so that in no place 
is a student very far from the experimental point of 
view. Many of the experiments are _ intended 
apparently to be done only by the lecturer, but fifty- 
seven are specially described as instructions to a 
student. This double method involves considerable 
repetition, as the same statement which is made in the 
general text often appears again in the description 
of the experiment. No doubt, however, Dr. Glaze- 
brook has found by experience that a junior student 
can hardly be told a thing too often, and repetition 
certainly does not err on the side of indefiniteness. 
Again, there is a considerable amount of repetition in 
the text itself. A general induction is made from some 
experiment, and this leads to a definition. The de- 
- finition in many cases consists only of a repetition of 
the previous statements in a rather more formal shape, 
This, again, may be an advantage from the student’s 
point of view, but it must be admitted that it tends to 
NO. 1781, VOL. 69] 
| quantities. 
| pp 38, 39, and there is no hint given of this. 
| course, to the ordinary student this does not matter— 
make the book rather slow. We cannot imagine any- 
one (except a reviewer) taking it up and reading until 
the small hours before putting it down. However, it 
is essentially a class book, and the student may acquire 
an enthusiasm for science from his teacher, who will 
amplify the somewhat categorically imparted inform- 
ation, hence the lack of more life is not so important. 
The statements made are usually clear and logical. 
In some cases we are not sure of the logic. Thus, take 
the following sentence :— 
““We have already seen that the electrification of a 
conductor may be the manner in which we recognise 
a state of stress set up in the dielectric round the 
conductor ’’ (p. 40). 
Should not the logic of this sentence be inverted? 
Is it not the stress in the medium which is directly 
investigated, and from which the state of electrification 
is inferred ? 
Again, in stating the law of electric force, it is 
asserted to follow 
“as a result of the experiments, that when two 
similarly charged bodies are at a distance apart which 
is great compared with their dimensions, there is a 
repulsion between them which is proportional to the 
product of their charges,’’ &c. (p. 44). 
Is it not more logical to say that we measure the 
electric charges of bodies as being proportional to the 
mechanical forces which arise in consequence of 
them ? 
Again, the ‘ joule’’ is defined in terms of electrical 
This reversal of the true logical order 
will mislead the student, who will fail to see that it 
is a purely mechanical quantity. 
These may seem merely finicking criticisms, but 
those of us who come largely into contact with students 
know how difficult it is to eradicate illogical notions 
acquired during their early training. 
In some cases the information given is not sufficient. 
Thus, while considerable use is made of lines of force, 
we are not told how they are drawn so as to represent 
the intensity of the field. 
Again, the lines in the diagrams on pp. 36, 37, are 
drawn on a completely different system from those on 
Of 
he is accustomed to consider physics an _ esoteric 
science; but how confusing to the real student who 
tries to make out what the diagrams mean. 
Again, tubes of force suddenly appear (without in- 
troduction) on p. 186 instead of lines. 
On p. 377 it is stated that 
‘“‘ the total E.M.F. round the secondary is proportional 
to the total change in the number of lines of induction 
linked with it.”’ 
The whole chapter on electromagnetic induction, — 
indeed, deals only with the total E.M.F. It is no- 
where defined—the student will think it identical with 
electromotive force. 
The figures are very good and instructive. Fig. 77, 
which shows the screening action of an iron ring, 
would be improved if the refraction of the lines at the 
surface of the iron were correctly represented. Again, 
the lines do not crowd between the cake and cover 
