bscure. It would seem that subjects so simple and beautiful as these
could not be rendered difficult of comprehension, except by the most
awkward treatment; and yet we know of no work previous to that of Dr.
Youmans which does not utterly fail to give the general scientific
reader any idea whatever of their nature and theory. Here, however, they
are explained with clearness and elegance, and their bearing on the
undulatory theory of light is distinctly shown. As other instances of
most admirable exposition, we may call attention to the paragraphs on
crystallization, on the atomic theory, on isomerism and allotropism, on
diamagnetism, magnetic induction, and electric "currents," on the
sources of heat, on the chemical and thermal spectra, on the correlation
and equivalence of the forces, on the theory of ozone, on the
exceptional expansion of water and the supposed complexity of its atom,
on the structure of flame, on the constitution of salts, on the colloid
condition of matter, on types and compound radicles, on the dynamics of
vegetable growth and the production of animal power, and, above all, to
the passage which describes the phenomena of latent heat. Throughout, in
treating of these subjects, the author's felicity of exposition never
fails him. The most difficult phenomena are rendered perfectly easy of
comprehension, and their mutual relations are not left out of account.
Each set of facts is treated, not as forming an isolated body of truth,
but as an integral portion of the complex and logically indivisible
universe. In this respect Dr. Youmans's work is far superior to the
recent production of Dr. Hooker, in which, for example, the mere
existence of such a doctrine as that of the correlation of forces is
grudgingly noticed, and its ultimate significance entirely overlooked.

Far different is Dr. Youmans's treatment of the same doctrine. Indeed,
we think that the chapters on chemical physics form the most
interesting portion of his work, and their value consists chiefly in the
constant reference to the modern ideas of force which pervades them. In
a work intended for the education of youth, such a feature cannot be too
highly praised. It is time that the old material superstitions about
force were eradicated from men's minds, and as far as possible from
their language. It is already more than half a century since Count
Rumford demonstrated the immaterial nature of heat, and Young
established the undulatory theor