"Train's just a going, sir," said he. " You've
not a minute to lose."

So Saxon bowed again, stammered something
about being "very sorry," and vanished.

Just as he had taken his seat, however, and
the train had begun to move, the guard appeared
at the window, tossed in a card, said something
which was lost in the shrill shriek of the driver's
whistle, and dropped out of sight.

Saxon picked up the card, which was rather
small for a lady's use, and read:

Then he was about to throw the card out of the
window; but checked himself, looked at it again,
and put it in his waistcoat-pocket instead.

She was very pretty," he thought; "and her
voice was very sweet. How glad I am that I had
no card about me!"

IS HEAT MOTION?

PROFESSOR TYNDALL has produced a book of
science, Heat considered as a Mode of Motion,
which has been pronounced more entertaining
than a novel; being, to most other books of its
class, what a dramatic judicial trial is to a printed
romance; what, a self-experienced adventure is to
a tale that is told. It is like penetrating into an
unknown country, in comparison with driving
along a hackneyed highway. The reader, like
the traveller, is conscious of the presence of an
Alpine region partially hidden by a curtain of
mist. But, through the influence of the
enchanter's wand and under the beaming rays of
his genius, the cloudy veil gradually rises,
displaying to us whole chains of facts, mountains
of truth, long perspectives of consequences, and
an expanse of horizon which is nearly boundless.
We peruse the exposition slowly, just as we
leisurely sip good wine, careful not to drink it
in too quickly. We dally with his statements
and linger over his argument, lest the pleasure
they give us should be too fugitive.

"What," it may perhaps be asked, "can
there be so very taking in the subject of heat?"

There is this: that you cannot consider heat
without glancing at the whole of the forces of
nature, and becoming acquainted with the
latest efforts of modern thought. A new
philosophy has recently arisen respecting the general
energies of the universe; and this philosophy
Professor Tyndall has endeavoured to bring
within the reach of persons of ordinary intelli-
gence and culture. Heat is one of those ener-
gies, and the connexion of this agent with the
rest is such, that if we master it perfectly, we
master all.

In the last volume of Household Words* a
sketch is given of this new philosophy, as set
forth in two admirable treatises, "The Correlation
of Physical Forces," by Mr. Grove, and
"The Monogenesis of Physical Forces," by Mr.
Smee; the sum of the whole being that the
various affections of matter which constitute
the main objects of experimental physics, viz.
heat, light, electricity, magnetism, chemical
affinity, and motion, are all correlative, or have
reciprocal dependence; that either may produce
or be convertible into any of the others. Thus,
heat may mediately or immediately produce
electricity, electricity may produce heat; and
so of the rest. In scientific manuals, only
scanty reference has, as yet, been made to the
modern philosophy of heat; and thus, the
public knowledge regarding it remains below
the attainable level. More than three years
ago† we attempted to popularise the newest
speculations as to what fire is, and what it is not.
* See Physical Force, p. 354
† All the Year Round, vol. vi., p. 393

That heat is motion is Mr. Tyndall's thesis.
The achievements of heat through the steam-
engine, he says, forced the question upon
thinking minds, "What is this agent, by means
of which we can supersede the force of winds
and rivers, of horses and men? Heat can
produce mechanical force, and mechanical force can
produce heat; some common quality must therefore
unite this agent and the ordinary forms of
mechanical power." This relationship once
established, the generalising intellect could pass
at once to the other energies of the universe.
It now perceives the principle which unites
them all; and that is the new philosophy which
sweeps before it the cruder notions of bygone
times. Calorie, the old-fashioned fluid of heat,
is abolished for evermore.

The instances given of the connexion between
heat and motion, are many of them absolutely
startling. Heat is developed in a muscle when
it contracts, as was proved by MM. Becquerel
and Breschet, by means of a modification of the
thermo-electric pile. MM. Billroth and Fick
have found that, in the case of persons who die
from tetanus or locked-jaw, the temperature of
the muscles, in consequence of the convulsive
strain, is sometimes nearly eleven degrees
Fahrenheit in excess of the normal temperature.
M. Helmholtz has found that the muscles
of dead frogs in contracting produce heat.
Arterial blood, we know, is charged with oxygen;
when this blood passes through a muscle at rest,
in an ordinary uncontracted state, it is changed
into venous blood, which still retains about
seven and a half per cent of oxygen. But
Professor Ludwig of Vienna and his pupils have
proved that if the arterial blood pass through a
contracted muscle—a muscle at work—it is
almost wholly deprived of its oxygen, the
quantity remaining amounting, in some cases,
to only one and three-tenths per cent. As a
result of the increased warmth and augmented
combustion within the muscles when in a state