the Royal Institution of Great
Britain.

A comparison of the volume before us with any of the previously
published treatises on Heat will afford a striking and almost startling
proof of the present activity of inquiry, and the rapid progress of
scientific research. The topics treated are the same. The first seven
lectures of the course deal with _thermometric_ heat, expansion,
combustion, conduction, specific and latent heat, and the relation of
this force to mechanical processes; while the remaining five treat of
_radiant_ heat, the law and conditions of its movement, its influence
upon matter, its relations to other forces, terrestrial and solar
radiation, and the thermal energies of the solar system. But these
subjects no longer wear their old aspect. Novel questions are presented,
starting fresh trains of experiment; facts assume new relationships, and
are interpreted in the light of a new and higher philosophy.

The old view of the forces, which regarded them as material entities,
may now be regarded as abandoned. Light, Heat, Electricity, Magnetism,
etc., which have hitherto been considered under the self-contradictory
designation of "Imponderable Elements," or immaterial matter, are now,
by common consent, beginning to be ranked as pure forces; having passed
through their material stage, they are regarded as kindred and
convertible forms of motion in matter itself. The old notions, that
light consisted of moving corpuscles, and that heat, electricity, and
magnetism were produced by the agency of various fluids, have done good
service in times past; but their office was only provisional, and,
having served to advance the philosophy of forces beyond themselves,
they must now take rank among the outgrown and effete theories which
belong to the infantile period of science. This change, as will be seen,
involves the fundamental conceptions of science, and is nothing less
than the substitution of dynamical for material ideas in dealing with
the phenomena of Nature.

The new views, of which Professor Tyndall is one of the ablest
expositors, are expressed by the terms "Conservation and Correlation of
Forces." The first term implies that force is indestructible, that an
impulse of power can no more be annihilated than a particle of matter,
and than the total amount of energy in the universe remains forever the
same. This principle has been well characterized by Faraday as "the
highest law in physical science which our