position of the earth on its axis and its movement in its elliptical
orbit influence the general amount of heat, it is rather to the
consequences of these in detail that we are called when we speak of
temperature. If the sun shone on a uniformly level surface, everywhere
of the same conducting and radiating power, there would be but little
difficulty in tracing the monotonous effects of temperature.

The reformer Luther, as eccentric as he was learned and sincere, is
reported to have said, that, if he had been consulted at the Creation,
he would have placed the sun directly over the centre of the world and
kept it there, to give unchanging and uniform light and heat! It is
certainly much better that he was not consulted. In that case, every
parallel of latitude would have been isothermal, or of equal mean
annual temperature. The seasons would have been invariable in
character. Some portions of the earth would have been scorched to
crispness, others locked up in never-changing ice.

Vegetation, instead of being universal, would have been confined to a
narrow zone; and the whole human race would have been driven together
into one limited habitable space, to interfere with, incommode, and
destroy each other. The arrangement is best as it is.

We find very important modifications of temperature, occasioned not
only by astronomical influences, but by local causes and geographical
characteristics. For while, as a general rule, the nearer we approach
the equator, the warmer we shall be, yet temperature is greatly
affected by mountains, seas, currents of air or water, by radiation,
by forests, and by vegetation. It is found, in fact, that the lines of
temperature, (the happy conception of Humboldt,) when they are traced
upon the map, are anything but true zones or circles.