DEAD OTe 
97 
THURSDAY, NOVEMBER 29, 1906. 
ALTERNATING CURRENTS. 
Alternating Currents: a Text-book for Students of 
Engineering. By C. G. Lamb. Pp. vi+325. 
(London: Edward Arnold, n.d.) Price ros. 6d. net. 
HIS book is designed to be a text-book for 
students of engineering, more particularly for 
those who are going through a course at the engineer- 
ing laboratory at Cambridge. In any attempt to 
write an account of alternating currents for such a 
purpose, the question arises at once, Out of all the 
materials at the disposal of the author, what should 
be selected as being most suitable, or on what prin- 
ciple should such a selection be made? The answer 
to this question may perhaps be best given by consider- 
ing the requirements of engineering students. 
Chiefly, perhaps, the mind must be trained to accurate 
thought; but, apart from this, which is common to 
all scientific education, a student should acquire a 
thorough knowledge of fundamental principles in 
such a way that he may have confidence in himself 
when he is faced with the various problems that con- 
stantly arise in the course of his professional career. 
Beyond this, he should be taught sufficient of the 
methods of procedure in common use, so that when 
he takes up his first appointment in a subordinate 
position he will be able to follow with intelligence 
the methods of practice used by his superiors. As Mr. 
Lamb remarks in his preface, details of actual prac- 
tice are unsuitable in such a book, and are best learned 
by actual contact with drawing-office work. 
If the book in question be examined in the light of 
these principles, it will be seen that the statements 
of the fundamental ideas are very clear, and are 
logically followed up. It might, perhaps, be sug- 
gested that there is a tendency to explain various 
actions by means of equations rather than by physical 
conceptions. One is somewhat reminded of the mathe- 
matical coach lecturing on optics, who introduced the 
subject of optical instruments with the remark that 
a telescope is defined by the equation K=o. Many 
students are naturally inclined to view physical 
problems in this way, and such a tendency should be 
checked, especially among intending engineers. 
With regard to the methods of procedure in common 
use, it cannot be said that this book is irreproachable. 
In particular, practically no mention is made of the 
necessity of designing apparatus to meet a given tem- 
perature specification. This necessity makes itself 
felt throughout almost the entire range of electrical 
apparatus, and yet with the exception of one brief 
paragraph the subject of temperature rise is not 
mentioned. A student reading this book with no 
other source of information at his disposal might be 
excused for imagining that apparatus was usually 
designed without any definite ideas as to its capacity, 
and was only rated after it had been manufactured 
and tested to see what it would stand, This must be 
regarded as an unfortunate omission. 
Turning now to the consideration of the book in 
detail, it should be remarked that a certain extent 
of previous acquaintance with elementary theory is 
NO. 1935, VOL. 75 | 
assumed, chiefly the theory of magnetism, including 
hysteresis and eddy currents, and a knowledge of 
vectors. The author has not attempted to introduce 
any symbolic treatment, no doubt very wisely. 
The first seven chapters cover the preliminary 
statements of the usual methods of treating alternate- 
current problems in general, also of measuring in- 
struments, and discuss the theory of the single-phase 
transformer. This piece of apparatus is regarded first 
of all in the light of a choking coil, for which the 
fundamental vector diagrams are obtained. Follow- 
ing this the analytical expressions for an actual trans- 
former are worked out, and methods are described 
whereby the regulation can be calculated. The fifth 
chapter concludes with a paragraph giving a few 
constants for a modern type, which might have been 
more valuable if some indication had been given as to 
how such constants vary. over a range of transformers 
for different outputs and frequencies, and with different 
load factors. Special types of transformer occupy 
the sixth chapter, in which mention might have been 
made of sucking—or booster—transformers, to be 
quite up to date; while the seventh chapter is devoted 
to efficiencies. 
Apart from the points mentioned, which are not 
important, the foregoing chapters may be said to be 
excellent both in matter and in manner. Unfortu- 
nately, the same cannot be said of the very brief 
mention of single-phase commutator motors which 
occupies the eighth chapter. This part gives one the 
impression of having been put in as an afterthought; 
neither the repulsion motor nor the compensated re- 
pulsion motor is mentioned, and the type of series 
motor illustrated is already antiquated; moreover, the 
self-induction of the whole motor cannot be reduced 
to that of the field coils alone (p. 95). 
The rest of the book is devoted to the considera- 
tion of alternators both as generators and motors, 
and of induction motors. Without following the 
treatment too closely, it may be remarked that wave 
forms are considered with reference to the presence of 
harmonics, the properties of concentrated and dis- 
tributed windings are set out, and towards the end of 
the book armature reaction is considered in detail. 
The treatment of the latter subject is based chiefly 
on the method of synchronous reactance, in which 
the whole reaction is considered simply as due to a 
single internal self-induction. This method has 
several drawbacks, and for practical work it is better 
to look upon the action of the armature as partly a 
demagnetising effect and partly a_ self-induction. 
This treatment is very simple, and sufficiently accu- 
rate if proper constants are taken. In chapter 
xxi. of Mr. Lamb’s work the armature reaction is 
dealt with in greater detail, and is split up into three 
components, viz. stray field reactance, cross and back 
reactances, each of which has its own magnitude and 
its own phase. It is stated that this method leads to 
very good results, but it is more cumbersome, and 
seems to contain as much liability to error as the 
method above alluded to. 
Space will not permit of more than a brief reference 
to many of the subjects dealt with. Induction motors 
are discussed with reference to the well-known Hey- 
FE 
