s being his own:--"What is heat? Is there any such
thing as an _igneous fluid_? Is there anything that with propriety can
be called caloric? We have seen that a very considerable quantity of
heat may be excited by the friction of two metallic surfaces, and given
off in a constant stream, or flux, in _all directions_, without
interruption or intermission, and without any signs of _diminution_ or
_exhaustion_. In reasoning on this subject, we must not forget that
_most remarkable circumstance_, that the source of the heat generated by
friction in these experiments appeared to be _inexhaustible_. It is
hardly necessary to add, that anything which any insulated body or
system of bodies can continue to furnish _without limitation_ cannot
possibly be _a material substance_; and it appears to me to be extremely
difficult, if not quite impossible, to form any distinct idea of
anything capable of being excited and communicated in these experiments,
except it be MOTION."

In style, Professor Tyndall's work is remarkably clear, spirited, and
vigorous, and many of its pages are eloquent with the beautiful
enthusiasm and poetic spirit of its author. These attractions, combined
with the comprehensiveness and unity of the discussion, the range and
authenticity of the facts, and the delicacy, originality, and vividness
of the experiments, render the work at once popular and profound. It is
s classic upon the subject of which it treats.

_My Days and Nights on the Battle-Field_. A Book for Boys. By
"CARLETON." Boston: Ticknor and Fields.

The literature of the war has already reached the dimensions of a
respectable library. The public mind at the instant of the outbreak felt
an assurance that it was to be one of the memorable epochs of mankind.
However blinded to the significance of the previous conflicts in the
forum and at the ballot-box, there was a sudden and universal instinct
that their armed culmination was a world-era. The event instantly
assumed its true grandeur.

The previous discussions seemed local and limited. They were squabbles,
we fancied, among ourselves, which did not touch the vitals of our
system, and in which the world without had neither lot nor interest.
Even when the fires of debate and division waxed hotter and hotter, and
began to break out in violent eruptions in Congress, Kansas, throughout
the South, and especially at Harper's Ferry, we still said, These are
political conflicts, mob-violences, raids,