are indispensable to the fertility of the earth. Without
suitable arrangements for their diffusion and distribution, and within the
limits of certain minima and maxima, it would not have been habitable, or
the design of its Creator perfected. These arrangements therefore exist,
and "while the earth remaineth seed time and harvest shall not cease." Few
and simple in their character, though necessarily somewhat complicated and
irregular in their operation, the ultimate result is always attained. A
beautiful system of compensations supplies the losses of every apparent
irregularity in one section or crop, by the abundance of others.

From the operation of these few, simple, connected, and intelligible
arrangements for the diffusion of heat and the distribution of moisture
over the earth, result all the phenomena which constitute the weather; and
by studying them, and their operation, we may acquire an accurate
knowledge of its "_Philosophy_."

The necessary heat is furnished, or produced, mainly by the direct action
of the sun's rays; and the most obvious feature in the arrangements for
its diffusion is that by which the sun is made to shine successively and
alternately upon different portions of the earth. Nothing animate or
organic could endure his burning rays, if they shone continuously or
vertically upon one point, or could exist without their occasional
presence. Hence the provision for a diurnal rotation, to prevent the
exposure of any portion of the globe to the action of those rays for
twenty-four consecutive hours, except for a limited period, and at a
considerable angle, in the polar regions. But the earth is spheroidal, and
a diurnal revolution would still leave that portion which lies under the
equator too much, and the other too little, exposed to the action of the
sun. This is obviated by an annual revolution of the earth around the sun,
and an obliquity of its axis, by reason of which the northern and southern
portions are alternately and, as far as the tropics vertically, exposed to
the sun; and it is made to travel (so to speak) from tropic to tropic,
producing summer and winter, and other important phenomena.

This obliquity and consequent change of exposure are in degree precisely
what the wants of the earth would seem to require. If it was greater, the
sun would travel further north and south, but the alternate winters would
be longer and more severe. If it was less, the end would not be as
perfectly