132 SCIENCE. 
be taken through a course of study in the ana- 
lytical theory of the alternator, the transformer, 
etc., before beginning the practical study of 
alternating current appliances. 
The separation of theoretical and practical 
treatises seems to us to be highly desirable, for 
our experience is that nothing obscures an ele- 
mentary treatise (that is, the elementary part) 
so much as the introduction of practical matter 
not needed for purposes of illustration, and we 
conceive that nothing is so annoying to a well 
instructed engineer as to have his engineering 
literature highly diluted with elementary mat- 
ter. 
Alternating Currents, by Alfred Still, is an ex- 
cellent, clean cut, elementary treatise. Pages 
1 to 116 are devoted to the general principles 
of alternating currents and the remainder is de- 
voted to the theory of the transformer. In 
reading this book one has a desire to know what 
the author might have to say of the synchronous 
motor and rotary converter, and of the induc- 
tion motor, so simply and satisfactorily is the 
theory of the transformer worked out. One 
cannot of course judge whether or not the au- 
thor realizes the paramount importance of 
these machines and the need fora simple ex- 
position of their theory. 
In speaking of the expression B—yH the 
author says that ‘‘the point which is not gen- 
erally clearly explained is that there is no ne- 
cessity whatever, to consider the iron core re- 
moved, or even to imagine longitudinal holes 
drilled through the mass of the iron in drder to 
understand what is meant by H in the above 
relation.’? However, we do not know what 
actually takes place in magnetized iron and in 
the specification of the state of magnetization 
of a rod we can, and do, specify only what is 
happening outside the rod or in holes drilled 
through the rod. 
Tn speaking of magnetic leakage the author 
devotes his attention mainly to that case in 
which the trend of the useful magnetic flux 
would be but little altered by the removal of 
all iron parts the flux being, of course, reduced 
in value. In this case the magnetic leakage 
generally decreases with increasing excitation. 
The most frequent case in practice, however, is 
that in which the trend of the useful flux would 
[N. S. Von. X. No. 255. 
be greatly altered by the removal of the iron 
parts, as for example in the dynamo. In this 
case the magnetic leakage increases with in- 
creasing excitation. 
Mr. Still’s book ‘‘ has been written not only 
for engineering students, but also for those en- 
gineers who are but slightly acquainted with 
alternating current problems.’’ We cannot 
agree with the author that for this class of 
readers analytical methods are unsuitable for 
the solution of alternating current problems. 
The engineer who attempts the graphical 
method soon finds it to be impracticable ex- 
cept only as an aid in the formulation of analy- 
tical solutions. Steinmetz’ method seems to us 
to be the simplest method for obtaining numer- 
ical results and the only method to be called 
practicable. 
Alternate currents in practice, translated from 
the French by Francis J. Moffett, is a good dis- 
cussion of a great variety of practical alterna- 
ting current apparatus with comparatively little 
useless or misplaced elementary matter. Mr. 
Moffett says that to the best of his knowledge 
there is no work in existence in England at the 
present time which treats in a practical manner 
the whole range of alternating currents of elec- 
tricity and we do not know of any such work 
in America for the admirable works of Bedell, 
Jackson and Steinmetz are distinctly theoret- 
ical. 
W. S. FRANKLIN. 
Das Tierreich Sporozoa. By ALPHONSE LABBE. 
Eine Zusammenstellung und Kennzeichnung 
der rezenten Tierformen. Herausgegeben 
von der Deutschen Zoologischen Gesellschaft. 
5 Lieferung. Protozoa, Sporozoa. Berlin, 
Friedlander & Sohn. 1899. Pp. xx + 180. 
As indicated by the descriptive title of Das 
Tierreich, a zoological dictionary of which 
Franz Eilhard Schultze is the chief editor, it is 
no part of the undertaking to give a general 
account of the classes of animals considered, 
but merely recognizable descriptions of all 
known species. For the present volume—the 
Sporozoa—a better man than Alph. Labbé could 
not have been chosen, and, so far as the sporu- 
lation is concerned and the determination of 
species through spores, or the hosts of the 
