: 
May 22, 1873] © 
Chap. III. is on acoustics ; Chap. IV. on light ; Chap. V- 
on magnetism ; Chap. VI. on electricity; Chap. VII. on 
heat. It may be remarked that the figures are drawn to 
scale, and further illustrations of the details are added 
whenever necessary. 
As a fair specimen of the illustrations and descriptions 
we may refer to Article 121, wherein is described Miiller’s 
apparatus for studying experimentally the free falling of a 
body. This beautiful contrivance is for the purpose of 
causing a point vibrating horizontally to trace a curve 
upon a board descending vertically. From the form of 
the curve the law of falling bodies is deduced. In Chap. 
IV. we meet with many interesting contrivances : for 
example, Fig. 433 represents an arrangement for showing 
the principle of the rainbow experimentally by the aid of 
spheres of glass. This chapter is concluded by a practical 
lesson in photography. Many of tl:e figures in Chap. VI. 
will be found to represent electric instruments which are 
manifestly great improvements on forms in ordinary use, 
As an example we refer to the Rheostat, Fig. 775. 
Considering the book has already reached such portly 
dimensions we can hardly complain of omissions. We 
are, however, of opinion that the space at the disposal of 
the author might have been more judiciously employed if 
some of the apparatus which he has described were 
omitted and some instruments which he has passed over 
were inserted instead. To illustrate this remark we may 
refer to the chapters on mechanics. We there find a 
number of ingenious contrivances generally pretty well 
known, but we also meet with toys like those described in 
articles 66 and 67 which could, we think, have been very 
well dispensed with. On the other hand we seek in vain 
in the same chapter for a full account of Willis’s system 
of mechanical apparatus. To say that this ingenious 
system would, with trifling additions, enable all the me- 
chanical experiments described by Dr. Frick to be per- 
formed is to give a very inadequate idea of its resources. 
In the hands of a competent experimenter Willis’s ap- 
paratus will be found to provide in a substantial form the 
principal parts necessary for nearly every conceivable ex- 
periment in mechanical philosophy. The framework of 
this apparatus is so useful in almost any physical research 
that we cannot conceive how it could have been omitted 
from “Physikalische Technik,” had the author of that work 
been acquainted with the writings of Prof. Willis. We 
think also that some of the host of merely qualitative ex- 
periments described for the purpose of illustrating centri- 
fugal tendency (Article 124) might very well be omitted. 
On the other hand, we miss Smeaton’s machine, which, 
admitting as it does of exact quantitative results being 
determined. is perhaps, next to Atwood’s machine, the 
most useful instrument we have for illustrating the truths 
of dynamics. 
We are tempted to think that Dr. Frick is not ade- 
quately acquainted with English scientific - literature. 
This opinion receives some confirmation when, on turn- 
ing over 238 closely-printed pages which describe 
electrical apparatus, we fail to see Sir William Thom- 
son’s beautiful instruments described ; nor on turning 
to the Index do we even find the name of that philo- 
sopher mentioned. 
, Although we decidedly think this book might have been 
better, yet. we decidedly think that it is very good, and we 
NATURE 
63 
cordially recommend it to the notice of physicists and 
lecturers, who will certainly find it useful. 
OUR BOOK SHELF 
Electricity. By R. M. Ferguson, Ph,D., F.R.S.E. (W. 
and R. Chambers.) 
WE regret that the Elementary Treatise on Electricity 
has not been revised by its author since its first appear- 
ance. For example, useful as is the chapter on the 
absolute measurement of an electric current, its useful- 
ness to students would be increased by a fuller and more 
detailed explanation. At the foot of p. 159 it is stated 
that “the heating effect (of the current) depends on 
the strength of the current and the-resistance.” It should 
be the sguare of the strength of the current into the 
resistance, as is correctly stated ina preceding paragraph. 
On p. 153 there is a mistake in the calculation of the 
quantity of water decomposed by a current ; 60c.c, X tan. 
514=75 c.c., and not 80 c.c., as is stated, and afterwards 
assumed. A description of the sine-galvanometer ought 
hardly to have been omitted, and a fuller explanation, 
together with an engraving of Thomson’s reflecting 
galvanometer, ought surely to be given. There is also 
but a meagre account of the induction coil, and the 
function of the condenser is not explained: the term 
rheotom instead of contact-breaker, looks pedantic, and 
may puzzle some readers. But the most faulty part of 
the book in our estimation is the singularly obscure 
and misleading manner in which the terms Electric 
Quantity and Tension are defined on p. 64. Tension is 
spoken of as synonymous with electric depth, or as the 
French say, electric thickness; whereas the tension, 
pressure, or power of discharge possessed by any electri- 
fied point, varies as the sgware of the electric depth at that 
oint. * 
. The first part of this text-book relates to magnetism 
and more evident care has been bestowed on this portion. 
The charts of isogonic and isoclinic lines are most useful, 
and so also are the chronological appendices, in which a 
brief scientific history of each subject is given. But why 
could not the dip and declination be given for a later 
year than 1865? It is said on page 16 that two magnetic 
needles are absolutely necessary to show “the power of 
the earth in determining the position of the needle,” and 
that “if it were possible to hang aneedle in the air so as 
to leave it perfectly free to take any position, it would show 
us fully the directive action of the earth.” Is it not pos- 
sible to buoy a magnetic needle in water, or sink it in 
mercury, so that the action of gravity may be neutralised, 
and the directive influence of the earth wholly come into 
play? Moreover, many dipping needles are made with a 
swivel pivot, by means of which the declination and dip 
are roughly shown at the same time. Two other blun- 
ders we notice in the part on magnetism. On page 4, 
speaking of a “small magnetic bar or needle,” Dr. Fer- 
guson says that “if both poles of the needle are attracted 
indifferently by any end of it [a bit of iron], it is not 
magnetic.” This is as slipshod in its science as it is in 
its English, for it is precisely the test of a magnetic body 
that it does attract either end of the needle ; magnetic 
should of course read magnetised, and so again a few 
lines lower down. The other blunder is on page 14, 
where it is said that “cobalt is attracted by the magnet 
at the highest temperatures.” It is well known, and can 
easily be shown as a class experiment, that cobalt loses 
its magnetic character at a white heat. But in spite of 
these errors, Dr. Ferguson’s “ Electricity” is a book that 
has been of much use to both teachers and students of 
science. Its obvious merits lead us to hope that a revise 
edition may find it free from the defects to which we have 
drawn attention. 
