42 
NATURE 
[May 15, 1873 
on — ———————————————————————————— 
gently for some broad scheme of reform which may be 
introduced without danger, which will render all fellow- 
ships unnecessary, which will at once provide for the pro- 
fessional student and the original investigator, and that 
in such a way that an ignorant Parliament shall have no 
excuse for tampering with it. And if they do this quickly, 
they may do it before the Association for Academical 
Organisation has begun to stretch its limbs. 
LONGMANS’ TEXT-BOOKS OF SCIENCE 
Electricity and Magnetism. By Fleeming Jenkin, 
F.R.SS. L. and E., M.I.C.E., Professor of Engineering 
in the University of Edinburgh. (London : Longmans 
and Co., 1873.) 
HE author of this text-book tells us with great truth 
that at the present time there are two sciences of 
electricity—one that of the lecture-room and the popular 
treatise; the other that of the testing-office and the 
engineer’s specification. The first deals with sparks and 
shocks which are seen and felt, the other with currents 
and resistances to be measured and calculated. The 
popularity of the one science depends on human 
curiosity ; the diffusion of the other is a result of the 
demand for electricians as telegraph engineers. 
The text-book before us, which is the work of an 
engineer eminent in telegraphy, is designed to teach the 
practical science of electricity and magnetism, by setting 
before the student as early as possible the measurable 
quantities of the science, and giving him complete in- 
structions for actually measuring them. 
“ The difference between the electricity of the schools 
and of the testing office has been mainly brought about 
by the absolute necessity in practice for definite measure- 
ment. The lecturer is content to say, under such and 
such circumstances, a current flows or a resistance is 
increased. The practical electrician must know how 
much resistance, or he knows nothing ; the difference is 
analogous to that between quantitative and qualitative 
analysis.” 
It is not without great effort that a science can pass 
out of one stage of its existence into another. To 
abandon one hypothesis in order to embrace another is 
comparatively easy, but to surrender our belief in a mys- 
terious agent, making itself visible in brilliant experi- 
ments, and probably capable of accounting for what- 
ever cannot be otherwise explained; and to accept the 
notion of electricity as a. measurable commodity, which 
may be supplied at a potential of so many Volts at so 
much a Farad, is a transformation not to be effected 
without a pang. 
It is true that in the last century Henry Cavendish led 
the way in the science of electrical measurement, and 
Coulomb invented experimental methods of great pre- 
cision. But these were men whose scientific ardour far 
surpassed that of ordinary mortals, and for a long time 
their results remained dormant on the shelves of libraries. 
Then came Poisson and the mathematicians, who raised 
the science of electricity to a height of analytical splen- 
dour, where it was even more inaccessible than before to 
the uninitiated. 
' And now that electrical knowledge has acquired a 
commercial value, and must be supplied to the telegraphic 
world in whatever form it can be obtained, we are per- 
haps in some danger of forgetting the debt we owe to 
those mathematicians who, from the mass of their unin- 
terpretable symbolical expressions, picked out such terms 
as “ potential,” “ electromotive force” and “ capacity,” re- 
presenting qualities which we now know to be capable of 
direct measurement, and which we are beginning to be 
able to explain to persons not trained in high mathe- 
matics. 
Prof. Jenkin has, we think, made great progress in the 
important work of reducing the cardinal conceptions of 
electromagnetism to their most intelligible form, and 
presenting them to the student in their true connection. 
The distinction between free electricity and latent, 
bound, combined, or dissimulated electricity, which 
occurs so frequently, especially in continental works on 
electricity, is not, so far as we can see, even alluded to in 
these pages ; so that the student who takes Prof. Jenkin 
as his sole guide will not have his mind infected with a 
set of notions which did much harm in their day, On 
the other hand, terms which are really scientific—the use 
of which has led to a clearer understanding of the 
subject—are carefully defined and rendered familiar by 
well-chosen illustrations. 
Thus we find that men of the most profound scientific 
acquirements were labouring forty years ago to discover 
the relation between the nature of a wire and the strength 
of the current induced in it. By the introduction of the 
term “electromotive force” to denote that which produces 
or tends to produce a current, the phenomena can now 
be explained to the mere beginner by saying that the 
electromotive force is determined by the alterations of the 
state of the circuit in the field, and is independent of the 
nature of the wire, while the current produced is mea- 
sured by the electromotive force divided by the resistance ~ 
of the circuit. To impress on the mind of the student 
terms which lead him in the right track, and to keep out 
of his sight those which have only led our predecessors, 
if not. ourselves, astray, is an aim which Prof. Jenkin 
seems to have kept always in view. 
To the critical student of text-books in general, there 
may appear to be a certain want of order and method in 
the first part of this treatise, the different facts being all 
thrown into the student’s mind at once, to be defined and 
arranged in the chapters which follow. But when we con- 
sider the multiplicity of the connexions among the parts 
of electrical science, and the supreme importance of never 
losing sight of electrical science as a whole, while en- 
gaged in the study of each of its branches, we shall see 
that this little book, though it may appear at first a mighty 
maze, is not without a plan, and though it may be diffi- 
cult to determine in which chapter we are to look for any 
particular statement, we have an excellent index at the 
end to which we may refer. 
The descriptions of scientific and telegraphic instru- 
ments have all the completeness and more than the concise- 
ness which we should look for from a practical engineer, 
and in a small compass contain a great deal not to be 
found in other books. The preface contains an outline of | 
the whole subject, traced in a style so vigorous, that we 
feel convinced that the author could, with a little pains 
bestowed here and there, increase the force of his reason- 
ing by several “ Volts,” and at the same time diminish by 
