6 
1 TREATISE ON ELECTRICITY.} 
ie the treatise on electricity referred to below 
the author aims at the production of “an 
advanced text covering both the theoretical and 
practical sides of the subject, so far as this can 
conveniently be done in a single volume.” A 
somewhat obscure statement in the preface in- 
Photographed by Prof.4J. Zenneck. 
ou Llecwichy 
Fic. 1.—Damped Oscillatory Discharge, 
forms us that “though complete in itself, the book 
is not intended for beginners, who may be sup- 
posed to have read one of the excellent elementary 
treatises available, such as Whetham’s ‘ Theory 
of Experimental Electricity.””’ As matter of 
fact, the first half of the book contains 
curious combination of advanced mathematics and 
elementary physics. In the present 
state of our public-school education, 
in which it is possible for a boy to 
a 
a 
complete his school course with 
practically no knowledge. of ele- 
mentary science, such a combination 
This part of the 
treatise might’ therefore be recom- 
mended to a mathematical honours 
student taking up for the first time 
the study of electricity. 
In the chapter, which is 
a mathematical introduction, the 
author discusses the transformation 
of Gauss, the theorems of Green and 
may be necessary. 
first 
of Stokes, the equation of wave- 
motion, and the Bessel functions. 
In the second ch ipter he gives an peRes— eto 
elementary -description of the be- 
haviour-of magnets and the plotting of lines of 
force with iron filings. This and the seven 
chapters -followi: have been kept fairly simple 
and ‘are intended to contain all the principles 
necessary for a right appreciation of the subject. 
rhe author is to be congratulated on the freshness 
(«c eT ar th Clee 6) Pac eae Berk 
NG. 2445, VOL. 98 | 
NATURE [ 
From 
SEPTEMBER 7, 
1916 
of his presentation even of familiar topics. 
Recent forms of apparatus are well described and 
illustrated, and some novel experiments are intro- 
duced. The method of exhibiting lines of electric 
force by scattering small crystals of oxalic acid 
on a cardboard sheet is interesting, and the result 
is well shown in Fig. 38. 
We notice that the term “electromotive force” 
(p. 110) is used as equivalent to “dif- 
ference of potential.” In our opinion 
this is a mistake; it is better to con- 
sider the E.M.F. as that which gives 
rise to a P.D. Thus in a cell on 
open Circuit the E.M.F. due to the 
chemical action of the constituents 
sets up a P.D, between the terminals 
which, inside the cell, is opposed to 
the E.M.F. When the terminals are 
joined by a conductor the P.D. 
between the terminals falls, but the 
E.M.F. of the cell (neglecting polar- 
isation) remains the same. In other 
cases an E.M.F. may arise from 
thermal effects or electromagnetic 
induction, 
One difficulty which always per- 
plexes a student of electricity is the 
significance of “magnetic induc- 
tion,” B. It was with a certain 
i atinuped se 
Treatise amount of pleasurable anticipation 
that we referred to Mr. Pidduck’s 
| treatment of this subject, only to be confronted 
1e Oscillatory Discharge of the Secondary of a Coupled Circuit. 
photograph by Prof. J, Zenneck. 
by the bald statement: “The vector B is called the 
magnetic induction, and the last equation may be 
written B=H-+ 471, where addition signifies addi- 
tion of rectangular components.” It is true that 
the reader is assured that he will appreciate the 
full importance of the vector B after reading the 
E ‘ ¢ From a 
From ‘ A Treatise un Electricity.” 
next chapter, dealing with the induction of cur- 
rents, but an appreciation of its importance is not 
the same as a‘clear realisation of its meaning. It 
is a remarkable fact that the term “ permeability ” 
is not mentioned in the index, nor does it appear 
to be once referred to in the text, 
The latter half of the book, containing chapters 
which form introductory accounts of special 
