NATURE 
265 
; 
ALTERNATING ELECTRIC CURRENTS. 
(1) The Principles of Electrical Engineering and 
their Application, By Prof. Gisbert Kapp. 
Vol. i. © Pp. xii+356. (London: Edward 
__. Arnold, 1916.) Price 18s. net. 
(2) A Treatise on the Theory of Alternating 
Currents. By Dr. Alexander Russell. Vol. ii. 
‘Second edition. Pp. xiv+566.¢ (Cambridge : 
At the University Press.) Price 15s. net. 
(3) Alternating Currents in Theory and Practice. 
By W. H. N. James. (Cambridge Technical 
Series.) Pp. viit353.. (Cambridge: At the 
_ University Press, 1916.) Price ros. 6d. net. 
abs progress of electrical knowledge and in- 
vention is so rapid and the ground covered 
so extensive that the trend of its literature is for 
the most part in the direction of books or mono- 
graphs on special departments of it written: 
by experts.’ On the other hand, as the existing 
complete treatises become antiquated or too bulky 
by additions, the necessity arises for rewriting 
the subject from a more modern point of view. 
(1) The aim of Prof. Kapp’s book, the first 
volume of which is before us, is to furnish the 
engineering student with a-couple of volumes 
wherein the-principles. and modern practice of 
electrical engineering are treated compactly, yet 
completely, with reference to the needs of the 
engineer rather than to those of the physicist. 
Although, for the sake of distinction, we divide 
engineering into various branches, engineers of all 
kinds are constantly called upon to .use applied 
electricity in. various. ways... Thus, a mechanical 
engineer may have to put up a three-phase motor 
to work a* pump, or a civil engineer may have to 
lay out an electric tramway system. Hence no one 
practising any branch of engineering can afford to 
be ignorant of the principles and methods of elec- 
trical engineering. A very commendable feature 
of Prof. Kapp’s book is that the purely mathe- 
matical aspect of the subject is kept well under | 
Testraint. Such mathematics as is used rarely 
goes beyond simple algebra or a simple differentia- 
tion or integration. This is a distinct advantage, 
as most engineering students are rather repelled 
by a book which bristles with mathematical 
symbols. Again, the verbal explanations are 
clear and terse, whilst the diagrams have a re- 
freshing air of originality and have not done duty 
in other books. 
The volume under review deals with general 
principles, and is divided into fifteen chapters. 
The first six comprise the discussion of electric 
conduction and resistance, its measurement, and 
the electrical measurement-of current and voltage 
generally. It would have been better if the con- 
nections of the two types of plug Wheatstone’s 
bridge, viz. the series and dial patterns, had been 
more fully illustrated. and described. In’ the 
description on p. 20 of the “Thompson double 
bridge” the name should be “Thomson,” as the 
NO. 2458, VoL. 98] 
THURSDAY, DECEMBER 7, 1016. . 
Jate Lord Kelvin was, prior to his peerage, .Sir 
William Thomson, The name is correctly spelt in 
‘a previous section on the Thomson-Varley bridge. 
The chapter on potentiometric measurements 
‘.contains much useful information. It seems, 
' however, to be forgotten that the writer of this 
review was the first person to suggest “setting 
the potentiometer ’’ by means of a standard cell 
of known voltage and a divided potentiometer 
wire, so as to make it a direct-reading instrument. 
Curiously enough, this method was first described 
by the writer in a now extinct paper called 
Industries in July and August, 1886, which at that 
time was edited by Prof. Kapp. 
In the section on standard cells (p. 31) the 
name “Carhard’’ is a misprint for “Carhart.’’ 
Chap. v., on the distribution of continuous 
| currents, contains some valuable information not 
commonly given in text-books. The analogy 
between an electric main tapped off at various” 
intervals and a beam loaded at. intervals with 
weights is very instructive, and the application of 
the same graphical method of ‘solution is» sug- 
gestive. bats} 
Chap. vii. introduces the reader to the prin-. 
ciples of electrostatics, and although there: is, 
nothing, of the nature of great novelty in it, the 
facts are well. set out. Prof: Kapp defines the 
electrical capacity as the quotient of:charge and, 
potential difference. We think that. the definition 
is better given in the form that the capacity is. 
measured bythe. charge required. to, raise «the 
conductor to unit potential when all other sur- 
rounding conductors are at zero potential. 
In some of the formule given for capacities the 
student may perhaps be puzzled by the custom of 
writing Im for log, or the natural logarithm, and 
lg for logy, especially when the letter 1 appears, 
as in formula 66 on p. 116, in the same expression 
for the length of the conductor. Also the decision 
to employ e for the dielectric constant is not a 
happy one. This Greek letter has for ages past 
| been consecrated to denote the base of. the 
| Napierian logarithms, viz. 2:71828, etc. 
Chap. viii., on applied electrostatics, contains 
| much valuable matter of a practical kind, especi- 
ally on the subject of cable insulation. Chaps. 
ix. and x. deal with the subject of magnetism and 
electromagnetism in an _ interesting. manner. 
_ There is.on p. 162 another little misprint in a 
proper name in a reference to .“‘ Hatfield’s ” man- 
| ganese steel. This should, of course, be ‘ Had-. 
| field.” Chap. xi. covers elementary. electro- 
dynamics, and the information given is kept well 
in touch with practice, as, for instance, in the 
remarks on p. 223 on the method of reducing. the 
time constant of motor field circuits. On p. 208, 
second line, “Lenze’s law” should be ‘“Lenz’s 
| law.’’ pane 
The last chapter, xv., discusses alternating 
currents, and gives in compact form most of the 
necessary information. Altogether the book is 
one which can be strongly recommended, and we 
shall look forward with interest to the second 
volume as likely to contain much of great value 
Pp 
