process of winding up, while the formation of an
animal is a process of running down. This is
the rhythm of nature as applied to animal and
vegetable life. Plants are the economisers,
animals are the spendthrifts, of vital energy
derived from the sun.

Measured by human standards, writes Dr.
Mayer, the sun is an inexhaustible source of
physical energy. This is the continually wound–up
spring which is the cause of all terrestrial
activity. The vast amount of force sent by the
earth into space in the form of wave motion
(radiation) would soon bring its surface to the
temperature of death. But the light of the
sun is an incessant compensation. It is the
sun's light, converted into heat, which sets our
atmosphere in motion, which raises the water
into clouds, and thus causes the rivers to flow.
The heat developed by friction in the wheels of
our wind and water mills, was sent from the sun
to the earth in the form of vibratory motion.

Nature stores up the light which streams
earthward from the sun—converting the most
volatile of all powers into a rigid form, and
thus preserving it for her purposes—by means
of plants. The vegetable world constitutes the
reservoir in which the fugitive solar rays are
fixed, suitably deposited, and rendered ready for
useful application. With this process the existence
of the human race is inseparably
connected. The physical force collected by plants
becomes the property of another class of
creatures—of animals. The living animal
combines combustible substances belonging to the
vegetable world, and causes them to reunite
with the oxygen of the atmosphere. Parallel
to this process, runs the work done by animals,
which is the end and aim of animal existence.

The question is naturally asked, Has not the
human will, power to create strength, energy,
and endurance? Look at the different
conduct of different individuals, under difficulties,
whether moral or physical. Look at two men
upon a mountain-side, with equal health and
bodily strength. The one will sink and fail;
the other, with determined effort, scales the
summit. Has not volition, in this case at least,
a creative power, a faculty of calling up force out
of nothing—that is, out of no material source?

As a climber ascends a mountain, heat
disappears from his body; the same statement
applies to animals performing work. For every
pound raised by a steam-engine, an equivalent
quantity of its heat disappears; for every
step the climber ascends, an amount of heat,
equivalent jointly to his own weight and the
height to which it is raised, is lost to his body.
It would appear to follow from this, that the
body ought to grow colder in the act of climbing
or working; whereas universal experience
proves it to grow warmer. The solution of the
seeming contradiction is found in the fact, that
when the muscles are exerted, augmented
respiration and increased chemical action set in.
The bellows which urge oxygen into the fire
within are more briskly blown; and thus, though
heat actually disappears as we climb, the loss is
more than compensated by the increased activity
of the chemical processes. Nevertheless,
if our frame be heated by bodily exercise, we
must not forget that it is at the expense of our
stock of fuel. Physically considered, the law
that rules the operations of the steam-engine
rules the operations of the climber. The strong
will can draw largely upon the physical energy
furnished by the food; but it can create nothing.
The function of the will is to apply and direct,
not to create. The proof lies in the need of rest,
and in the prostration often felt after unusual
effort, even when successful.

When we augment the temperature of the
body by labour, a portion, only of the excess of
heat generated is applied to the performance of
the work. Suppose a certain amount of food to
be oxidised, or burnt, in the body of a man in a
state of repose; the quantity of heat produced
in the process is exactly that which we should
obtain from the direct combustion of the food
in an ordinary fire. But, suppose the oxidation
of the food to take place while the man is
performing work; the heat then generated in the
body falls short of that which could be obtained
from direct combustion. An amount of heat is
missing, equivalent to the work done.
Supposing the work to consist in the development of
heat by friction, then the amount of heat thus
generated outside of the man's body, would be
exactly that which was wanting within the body,
to make the heat there generated equal to that
produced by direct combustion.

It is easy (by means of the "mechanical
equivalent") to determine the amount of heat
consumed by a mountaineer in lifting his own body to
any elevation. The Professor—may his shadow
never grow less!—when lightly clad, weighs one
hundred and forty pounds. What is the amount
of heat consumed, in his case, in climbing from
the sea level to the top of Mont Blanc?

The height of the mountain is fifteen thousand
seven hundred and seventy-four feet; for
every pound of his body raised to a height of
seven hundred and seventy-two feet, a quantity
of heat is consumed, sufficient to raise the
temperature of a pound of water one degree Fahr.
Consequently, on climbing to a height of fifteen
thousand seven hundred and seventy-four feet,
or about twenty and a half times seven hundred
and seventy-two feet, he consumes an amount of
heat sufficient to raise the temperature of one
hundred and forty pounds of water, twenty and a
half degrees Fahr. If, on the other hand, he
could seat himself on the top of the mountain
and perform a glissade down to the sea level,
the quantity of heat generated by the descent
would be precisely equal to that consumed in
the ascent.

Measured by one's feelings, the amount of
exertion necessary to reach the top of Mont
Blanc is very great. Still, the energy which
performs this feat would be derived from the
combustion of some two ounces of carbon. In
the case of an excellent steam-engine, about
one-tenth of the heat employed is converted into
work; the remaining nine-tenths being wasted in