of animals; a change in her orbitual translation
round the sun, as determining the duration of the year, would, in like
manner, give rise to a marked effect. If the year were shorter, we
should live faster and die sooner.

[Sidenote: Animal and vegetable life interbalanced by material
conditions.]

In the present economy of our globe, natural agents are relied upon as
the means of regulation and of government. Through heat, the
distribution and arrangement of the vegetable tribes are accomplished;
through their mutual relations with the atmospheric air, plants and
animals are interbalanced, and neither permitted to obtain a
superiority. Considering the magnitude of this condition, and its
necessity to general life, it might seem worthy of incessant Divine
intervention, yet it is in fact accomplished automatically.

[Sidenote: And also appearances and extinctions determined.]

Of past organic history the same remark may be made. The condensation of
carbon from the air, and its inclusion in the strata, constitute the
chief epoch in the organic life of the earth, giving a possibility for
the appearance of the hot-blooded and more intellectual animal tribes.
That great event was occasioned by the influence of the rays of the sun.
And as such influences have thus been connected with the appearance of
organisms, so likewise have they been concerned in the removal. Of the
myriads of species which have become extinct, doubtless every one has
passed away through the advent of material conditions incompatible with
its continuance. Even now, a fall of half-a-dozen degrees in the mean
temperature of any latitude would occasion the vanishing of the forms of
warmer climates, and the advent of those of the colder. An obscuration
of the rays of the sun for a few years would compel a redistribution of
plants and animals all over the earth; many would totally disappear, and
everywhere new comers would be seen.

[Sidenote: Permanence of organisms due to immobility of external
conditions.]

The permanence of organic forms is altogether dependent on the
invariability of the material conditions under which they live. Any
variation therein, no matter how insignificant it might be, would be
forthwith followed by a corresponding variation in the form. The present
invariability of the world of organization is the direct consequence of
the physical equilibrium, and so it will continue as long as the mean
temperature, the annual supply of