
WLve2e.. 1On NATURE 
559 
ELECTRICITY AND MAGNETISM. type. _The usual accounts of magnetic phenomena 
1 i Electricit NG onetis By are given and the definitions here are normal. 
(1) plon i rehab s/h as a4 . eu Y | When electromagnetism is introduced a_ novel 
ie = Bee klin ae Macnu P. eed es definition of unit of current—the abampere—is 
(New York: The Macmillan Co.; London: given. This is defined as “the force per unit 
Macmillan and Co., Ltd., 1914.) Price 
1.25 dollars net. ' 
(2) Advanced Theory of Electricity and Magnet- 
ism. By W. S. Franklin and B. Macnutt. 
Pp. viit+300. (New York: The Macmillan 
Co.; London: Macmillan and Co., Ltd., 1915.) 
Price 2.00 dollars net. 
HESE books are written purely with a view 
to the practical application of electricity 
and magnetism. The choice of matter is excellent 
from this point of view, and it is all presented in 
a lucid, readable, and original manner, being 
illustrated with a large number of excellent 
diagrams. Experimental phenomena are usually 
described first, and to give students a grasp of 
their meaning mechanical analogies are given. 
Most of these analogies are excellent, but one 
gets the impression that on the whole too much 
attention is devoted to them, and that some of 
them could profitably be omitted. The introduction 
of the terms abampere, abvolt, and abohm for the 
absolute units of current, E.M.F., and resistance 
is a feature of the books. The electromagnetic 
system only is used, and in the advanced book 
the authors boldly declare that they are ignoring 
the electrostatic system altogether, a procedure 
that is perhaps wise, considering that the prac- 
tical aspect of the subject predominates. 
(1) The elementary book commences with a 
description of the most important phenomena in 
electricity from a practical point of view. Only 
the most elementary things in magnetism are 
described, and this part of the subject is of 
importance only in its relation to electricity. The 
action of electromagnets on wires carrying cur- 
rents is described very early in the book, and the 
reverse phenomenon—the action cf currents on 
magnets, which one is accustomed to find as a 
fundamental principle, does not appear till later. 
Great prominence is given to the “side push” on 
wires in a magnetic field (the term is the authors’), 
and, once described, its applications to the 
D’Arsonval galvanometer and to the dynamo 
follow. The tangent galvanometer is not 
described, as it is not a practical instrument. The 
“side push” is again employed in connection 
with magnetic intensity, which is defined as “the 
side force per abampere per unit length of wire.” 
The chief practical things to which attention is 
given are the dynamo, motor, transformer, and 
induction coil. 
(2) The advanced book is more of the usual 
NO. 2386, VOL. 95] 

length of wire per unit field intensity.” The 
meaning of the clear, but their 
wording is unfortunate, as they define current as 
the “force.” Whereas in the elementary book 
attention is devoted chiefly to the dyamo, etc., 
the advanced book seems to be written principally 
for telegraph engineers, as a very large amount 
of space is devoted to waves on wires. 
authors is 
As an 
application of permanent magnetism, a chapter is 
devoted to ships’ magnetism and the compensation 
of the compass. The chapters on electrostatics 
suffer from vagueness on account of the ignoring 
of the electrostatic system of units. For instance, 
the capacity of a parallel plate condenser is given 
as 
C (in farads)=1/B.a/x, 
is the area of one plate in sq. cm., 
x the distance apart of the plates, and B is a 
constant pan xITO.s again the 
practical aspect is kept in view, and space is 
devoted to such things as the design of insulators 
for cables and the capacity of a transmission line. 
Both books will be found of great value to 
students to whom the practical side of electricity 
and magnetism is the all-important thing, and in 
fact they will also be profitable to others if read in 
conjunction 
treatises. 
where “a” 
However, 
with some of the more abstract 
A large number of examples is given with each 
chapter. 15 Re 
OUR BOOKSHELF. 
By Prof. W. H. 
Mechanism of Steam Engines. 
James and M. W. Dole. Pp. viiit+170. (New 
York: ‘J. Wiley and Sons, Inc.; London: 
Chapman and Hall, Ltd., 1914.) Price 8s. 6d. 
net. 
THE purpose of the authors in producing this book 
has been to provide an elementary treatise on the 
kinematics of reciprocating steam. engines and 
steam turbines, and to make clear to the beginner 
the mechanical principles on which a steam engine 
operates. Special attention is given to valve gears 
and governing devices; the underlying heat theory 
is not treated. The book opens with a general 
discussion of a reciprocating steam engine, fol- 
lowed by types of single-valve engines. The 
valve ellipse, together with the Zeuner, Reuleaux, 
and Bilgram valve diagrams are described, and 
some typical single-valve problems are worked out. 
Centrifugal-throttling, crank-shaft and other 
governing devices are included, also riding cut-off 
valves and their governing devices. The book 
! closes with sections dealing with reversing gears, 
