a 
Fan. 18, 1883] 
forgotten the very important preliminary operation of 
blowing aside the froth and scum which accumulates on 
long standing, and which an injudicious skimmer is very 
apt to obtain and exhibit as his sole result. 
The book appears almost contemporaneously with 
Prof. S. P. Thompson’s little work on the same subject, 
which we noticed some months back, and may be taken 
as complementary to it. Although both are of the same 
scope, yet the area open to them was so wide that it 
seldom happens that they both contain equally full infor- 
mation on precisely the same subjects. 
The second volume which we here notice, viz. the 
compilation entitled “Electric Illumination,” is of very 
different appearance and scope. It isa handsome large 
octavo, well printed, and with admirable illustrations. It 
is not addressed to students, but to engineers and practical 
men, and it is a most useful summary of notices which 
have appeared in the pages of Ezgzneering, concerning 
dynamo machines, electric lamps, and the other parapher- 
nalia connected with the practical applications of electri- 
city. It aims, of course, more at completeness than at 
- judicious selection; and it therefore naturally includes a 
number of contrivances which are hardly likely to come 
into any notorious existence. 
While it is very useful as a book of reference, therefore 
itis scarcely calculated for ordinary reading, the style of 
the descriptions being not seldom tiresome, and giving 
one the usual dismal feeling of “letterpress’’ written up 
to a picture. Some of the sections are very full, as for 
instance that relating to the manufacture of Jablochkoff 
candles, where the account is so complete that the usual 
form of the Wheatstone bridge is depicted and carefully 
explained as if it were a specialty of the Jablochkoff 
system : while some other sections are distinctly meagre. 
At the same time it is only natural that some kinds of 
information should be easier of access than others, and 
that all that came to hand should be utilised. At the be- 
ginning of the book we havea sketch of the early history of 
dynamo machines, several admirable sketches of lines of 
force, and a very clear elementary exposition of the prin- 
ciples of magnetic induction. There are also very excellent 
and instructive skeleton figures of the Gramme and Sie- 
mens armatures, as designed by the late Antoine Breguet, 
though the writer of the article rather absurdly seems to 
take them as embodying researches which throw a new 
light on the action of the machines, instead of as useful 
and interesting illustrations of what was perfectly clear to 
every physicist. 
Throughout the book, in fact, one comes across various 
curious statements, which, if read hypercritically and 
pressed, would be either annoying or misleading; but still 
more frequently one is in the presence of a cautious 
vagueness which conceals the want of exact knowledge by 
the turning of a phrase, and one notices a laudable 
desire to avoid the ascription of either praise or blame 
and to take the odiousness out of all comparisons. 
But to say that some of the writers are often only half 
acquainted with their subject, and that they accordingly 
take precautions to avoid mistakes, is only to say that the 
book belongs to modern periodical literature; to that kind 
of literature, namely, which is written and read with the 
tacit understanding on both sides that in a few years at 
most it is sure to be out of date and forgotten, and that 
NATURE 
- THESE seven numbers form parts 6 to 12, 
265 
accordingly any serious labour expended on either its 
production or its assimilation would be labour misspent. 
Taken for what it is, however, it is difficult to imagine 
a more complete and handy publication of information 
for which at the present time there is a great demand, 
and the book will be welcomed by all who take an inte- 
rest, professional or otherwise, in those applications of 
electricity which are now so evidently imminent, and 
which must ultimately assume such vast proportions. 
OPN eA 
OUR BOOK SHELF 
Introductory Treatise on Rigid Dynamics. By W. Stead- 
man Aldis, M.A. (London: G, Bell and Sons, 1882.). 
THis little work is truly characterised by its above title. 
The portions of the subject selected by the author will be 
best indicated by the headings of the several chapters. 
An introductory chapter on kinematics is followed by one 
on D’Alembert’s principle ; general equations of motion 
of a rigid body ; impulsive forces. Chapter iii. treats of 
moments and products of inertia; Chapter iv. of motion 
round a fixed axis (centres of suspension, oscillation, and 
of percussion) ; Chapter v. of motion of a body with one 
point fixed ; and Chapter vi. of the motion of a free body. 
Chapter vii. discusses certain general principles, as con- 
servation of linear momentum, of moment of momentum, 
and of energy. In Chapter viii. miscellaneous problems 
are investigated, as of moving axes, initial motions, small 
oscillations, and “tendency to break.” As might have 
been expected from so accomplished a teacher, the expo- 
sition of the general principles is most clear, and these 
principles are fully illustrated by a capital selection of 
exercises, many of which are solved, and for the solution 
of many others hints are given at the end. We know of 
no better introduction to this difficult branch of study. 
The text is most carefully printed. 
Encyklopedie der Naturwissenschaften. UHerausgegeben 
von Prof. Dr. G. Jager (and seven other gentlemen). 
Erste Abtheilung (Parts 16, 19, 20, 22, 24, 26, 27). 
(Breslau : E. Trewendt, 1880, 1881.) 
z.e. the second 
volume of a “Handbuch der Mathematik,” edited by 
Dr. Schlémilch, the several treatises being written by 
Dr. R. Heger, Professor at Dresden. The pagination is 
continuous (1-963 pp.), and there are 235 woodcuts. 
The first treatise is on “Analytical Plane Geometry ” 
(pp. 1-194). The first 164 pages are devoted to the conic 
sections ; the mode of treatment, or rather the order of 
arrangement of propositions, is different from that of any 
English text-book with which we are acquainted, but 
approximates most closely to that of Dr. Salmon’s classi- 
cal work. It is a full, able, and interesting presentment 
of the properties of these curves. The remaining thirty 
pages are devoted to a rapid sketch of the principal 
known properties of curves of the third order, in which 
are embodied most, if not all, of the results of modern 
research. 
The second treatise is on “ Analytical Geometry of 
Three Dimensions’”’ (pp. 195-380); the third is on the 
“ Differential Calculus’? (pp. 381-568) ; and the last is on 
the ‘‘Integral Calculus’’ (pp. 569-902). 
This last work is broken up into three parts, of which 
the second treats of elliptic functions, the theta functions, 
and of elliptic integrals; the third is devoted to dif- 
ferential equations. 
There are two smaller works, one (pp. 903-928) on the 
method of least squares (Ausgleichungs-rechnung), and 
the other (pp. 929-957) on insurances (Renten-, Lebens-, 
und Aussteuer Versicherung). A list of works on the 
different subjects treated of in the “ Handbook” is given 
