In the preceding chapter we have alluded to the difficulties, or exigences necessarily arising from the modes in which heat and light are distributed over our earth; and of these, before we proceed, it may be proper to specify some of the most striking.

Had the heat and light derived from the sun to the earth, not been in any way modified; the equatorial and the polar regions would have been alike inaccessible to organic life. The heat within the tropics, and the cold towards the poles, would both have been destructive; while the intermediate regions would have been exposed to a constant succession of violent and sudden alternations of temperature, which would have rendered the present state of things no less an impossibility. In order, therefore, to render this earth an appropriate dwelling-place for such beings as at present occupy its surface, it was necessary that these extremes, and sudden vicissitudes of temperature should be in some way diminished or alleviated. Accordingly, these objects have been effected with the most consummate wisdom. Indeed, some of the most splendid instances of design in nature, are offered by those subsidiary arrangements, by which the difficulties, necessarily arising from the primary arrangements, are obviated and mitigated; and by which the greater portion of the earth's surface, has been made accessible to organic beings of the same general character.