aving been first lifted to the elevation from which it springs by the
power of the sun. The energy of winds is also due entirely to the
same power.

But there is still another work which the sun performs, and its
connection with which is not so obvious. Trees and vegetables grow
upon the earth, and when burned they give rise to heat, and hence to
mechanical energy. Whence is this power derived? You see this oxide
of iron, produced by the falling together of the atoms of iron and
oxygen; you cannot see this transparent carbonic acid gas, formed by
the falling together of carbon and oxygen. The atoms thus in close
union resemble our lead weight while resting on the earth; but we can
wind up the weight and prepare it for another fall, and so these atoms
can be wound up and thus enabled to repeat the process of combination.
In the building of plants carbonic acid is the material from which the
carbon of the plant is derived; and the solar beam is the agent which
tears the atoms asunder, setting the oxygen free, and allowing the
carbon to aggregate in woody fibre. Let the solar rays fall upon a
surface of sand; the sand is heated, and finally radiates away as much
heat as it receives; let the same beams fall upon a forest, the
quantity of heat given back is less than the forest receives; for the
energy of a portion of the sunbeams is invested in building the trees.
Without the sun the reduction of the carbonic acid cannot be effected,
and an amount of sunlight is consumed exactly equivalent to the
molecular work done. Thus trees are formed; thus the cotton on which
Mr. Bazley discoursed last Friday is produced. I ignite this cotton,
and it flames; the oxygen again unites with the carbon; but an amount
of heat equal to that produced by its combustion was sacrificed by the
sun to form that bit of cotton.

We cannot, however, stop at vegetable life, for it is the source,
mediate or immediate, of all animal life. The sun severs the carbon
from its oxygen and builds the vegetable; the animal consumes the
vegetable thus formed, a reunion of the severed elements takes place,
producing animal heat. The process of building a vegetable is one of
winding up; the process of building an animal is one of running down.
The warmth of our bodies, and every mechanical energy which we exert,
trace their lineage directly to the sun.

The fight of a pair of pugilists, the motion of an army, or the
lifting of his own body by an Alpin