e owing to an increase of
its density and moisture. Upon such a principle, the whole earth is
animated by the breath of life; the souls of brutes, which differ from
one another so much in intelligence, are only air in its various
conditions of moisture and warmth. He explained the production of the
world through condensation of the earth from air by cold, the warmth
rising upward and forming the sun; in the stars he thought he recognized
the respiratory organs of the world. From the preponderance of moist air
in the constitution of brutes, he inferred that they are like the
insane, incapable of thought, for thickness of the air impedes
respiration, and therefore quick apprehension. From the fact that plants
have no cavities wherein to receive the air, and are altogether
unintelligent, he was led to the principle that the thinking power of
man arises from the flowing of that substance throughout the body in the
blood. He also explained the superior intelligence of men from their
breathing a purer air than the beasts, which carry their nostrils near
the ground. In these crude and puerile speculations we have the
beginning of mental philosophy.

[Sidenote: Modern discoveries as to the relations of the air.]

[Sidenote: Inter-dependence of animals and plants.]

[Sidenote: Agency of the sun.]

I cannot dismiss the system of the Apollonian without setting in
contrast with it the discoveries of modern science respecting the
relations of the air. Toward the world of life it stands in a position
of wonderful interest. Decomposed into its constituents by the skill of
chemistry, it is no longer looked upon as a homogeneous body; its
ingredients have not only been separated, but the functions they
discharge have been ascertained. From one of these, carbonic acid, all
the various forms of plants arise; that substance being decomposed by
the rays of the sun, and furnishing to vegetables carbon, their chief
solid ingredient. All those beautifully diversified organic productions,
from the mosses of the icy regions to the palms characteristic of the
landscapes of the tropics--all those we cast away as worthless weeds,
and those for the obtaining of which we expend the sweat of our
brow--all, without any exception, are obtained from the atmosphere by
the influence of the sun. And since without plants the life of animals
could not be maintained, they constitute the means by which the aerial
material, vivified, as it may be said, by th