493 THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. [December 21,1S72. 
gested between different potentials and different levels. 
Positive electricity tends to run down from higher to 
lower potentials,‘and when it.does so run down, there is a 
loss of potential energy equal to the product of the 
quantity which runs down, and the difference of potential 
through which it runs down. When the quantity which 
runs down is unity, the loss of potential energy is equal 
to the loss of potential. It is usual to assume, as the 
zero of potential, the potential of the earth at the place 
of observation; but this assumption is not rigorously 
consistent with itself, since the existence of earth currents 
demonstrates that different potentials may exist at dif¬ 
ferent parts of the earth. Electrical potential is rigor¬ 
ously zero at places infinitely distant from all electricity. 
An equipotential surface is the surface over the whole of 
which there is the same value of potential.” We refrain 
from quoting any more, as we are afraid that the re¬ 
currence of the word potential will by this time have 
nearly exhausted our reader’s patience as well as our 
printer’s type. 
Whilst Professor Everett has thus raised the character 
of the work, we miss, to some extent, the clear and con¬ 
cise language of the Erench author. There are some 
parts, too, in which we fear the student is likely to be 
puzzled or misled. In sect. 97 we are told that capillary 
phenomena cannot be attributed to the action of the 
atmosphere, as they take place alike in air and in vacuo. 
But further on in sect. 97 D we read that two parallel 
vertical plates are _ urged together by capillary action, 
because “ the portion of liquid elevated between them 
is at less than atmospheric pressure, and therefore, is 
insufficient to resist the atmospheric pressure which is 
exerted on the outer faces of the plates.” The ex¬ 
planation of the charging of the prime conductor by an 
electric machine is also ambiguous; all that is said on 
the subject is that the rubbed glass “ gives off its elec¬ 
tricity through the points to the prune conductor, or, 
what amounts to the same thing, the conductors give off 
negative electricity, through the points to the positively 
electrified glass.” We do not think these two state¬ 
ments do amount to the same thing ; moreover, nothing 
is ^ said about the inductive influence exerted by the 
rubbed glass on the points, and which, necessarily, pre¬ 
cedes the discharge of the opposite electricity from their 
extremities. In current electricity there is no description 
of (Trove’s battery, andj in the explanation given of 
of Bunsen s no notice is taken of the chemical changes 
going on in the cell. Surely, also, it is a mistake to say 
in England that Bunsen’s form of voltaic battery is the 
one chiefly used for class experiments, though it may be 
true enough on the Continent. 
The weakest part of the original work to us appears to 
be the article on magnetism ; though Professor Everett 
has much improved it, more remains to be done. The 
whole of the large subject of diamagnetism and magneto- 
crystallic action are dismissed in a couple of short 
sections, and there is no mention whatever of diamag¬ 
netic polarity. We notice also one or two little inac¬ 
curacies and omissions that we are surprised to find have 
escaped Professor Everett s observation. Eor example, 
in sect. 80S an ingenious mode of determining the law 
of inverse squares as applied to radiant heat, is ascribed 
to Professor Tyndall, in both the French and English 
editions, when really it is due to Melloni. It will be 
found fully described in his famous work ‘ La Thermo- 
chrose.’ A reference to Professor Tyndall’s ‘ Heat as a 
Mode of Motion,’ at once shows how the mistake has 
arisen. There is a very good account of Melloni’s ex- 
periments in radiant heat, but an extremely poor record 
of v> uud has been done since. In this respect Atkinson’s 
edition of ‘ Gfanot’s ^Physics ’ is far superior. In the 
treatise on sound tnere are one or two noticeable omis¬ 
sions, we find no reference whatever to sensitive flames, 
noi to A\ heatstone s Ivaleidophone, nor to a recent and 
more perfect form of this same instrument known as the 
T onophant, which might well have been described in the 
paragraph relating to the various moles of producing- 
Lissajous’ figures. 
These are, however, but slight blemishes in a work of 
real excellence. Indeed, it is not too much to say that 
this work may be regarded as the best text-book in 
Experimental Physics that we possess in the English 
language. As we write this we cannot but feel that 
English physicists, and also English draughtsmen, ought 
to be ashamed of themselves. Why should we have to 
go to our continental neighbours for physical handbooks, 
and for cuts to illustrate them P Even in the two or three 
treatises on Physics written by Englishmen, the illustra¬ 
tions are in nearly every case almost unintelligible. 
Compare, for example the woodcuts in Balfour Stewart’s- 
‘ Physics,’ or Airy’s ‘ Magnetism,’ with the cliches 
of the exquisite French engravings to be found in the 
volume before us. How is it that with our South Ken¬ 
sington Schools of Art we cannot get a bit of apparatus 
decently engraved in England ? Illustrations are by no- 
means an unimportant adjunct to scientific text-books. 
Instrument-makers have to construct many pieces of 
apparatus solely from w T hat they see figured in a new 
work. To them, therefore, much depends on this matter. 
And those w r ho have not access to apparatus, are often 
misled in their conception of things by the rude unmean¬ 
ing cuts which are the common offspring of the English 
wood-engraver. 
Science and Commerce : their Influence on our 
Manufactures. A Series of Statistical Essays and 
Lectures, describing the Progressive Discoveries of 
Science, the Advance of British Commerce, and the- 
Conditions of our Principal Manufactures in the 
Nineteenth Century. By P. L. Simmonds. London 
Hardwioke. 1872. . 
Only a few persons comparatively have any idea of 
the mass of valuable, yet crude and undigested, informa¬ 
tion that is locked up in what are popularly known as 
“blue books.” Not many tasks, however, are more 
repulsive than to have to hunt for it through page after- 
page of consular reports or revenue returns, although 
many of them contain matter pregnant with interest to 
the public. Therefore when a book is published by so 
indefatigable a labourer in the field as Mr. Simmonds, 
the critic’s favour is already bespoken on its behalf. But 
even a desire to speak well of the work bearing the 
rather ambitious title placed at the head of this notice, 
cannot blind us to the fact that, as a whole, it is but a 
sorry specimen of book-making, and that a considerable 
proportion of it has little other raison d'etre than that it 
consists of lectures delivered by the author before various- 
audiences during the last twenty years. 
We say “ as a whole,” because taken apart there are- 
several essays containing valuable information upon 
various subjects, which information is made more readily 
available by an index. That this measure of praise can¬ 
not be extended to the whole book is the more regrettable, 
since the evil that vitiates it was one that was foreseen.. 
In the Preface the author says that his literary and pro¬ 
fessional engagements have prevented him from re¬ 
writing and condensing some of the treatises, but that he 
has supplemented them, and brought down the statistical 
and general information to the present time. The result 
is unfortunate, as, we think, will presently appear. 
The book opens with two lectures upon the obligations- 
of science to commerce, and on the vegetable, mineral 
and animal products entering into commerce, which 
formed the Travers’ course of Lectures at the London 
Institution in November, 1871. These lectures are based 
upon information of comparatively a recent date. But 
the next is a lecture on almost the same subject delivered 
in 1859, or twelve years previously , and the effect of 
reading this one after the other is sufficiently perplexing. 
To give a typical instance, after being told on p. 32 
that we import annually nearly 21,000,000 rattans, on 
