arth
in latitudes higher than that in which the surface or trade winds
flow. Thus along our Atlantic coast, and even in the body of the
continent, at times when the air is not controlled by some local
storm, the counter trade blows with considerable regularity.

The effect of the trade and counter-trade movements of the air on the
distribution of temperature over the earth's surface is momentous. In
part their influence is due to the direct heat-carrying power of the
atmosphere; in larger measure it is brought about by the movement of
the ocean waters which they induce. Atmospheric air, when deprived of
the water which it ordinarily contains, has very little
heat-containing capacity. Practically nearly all the power of
conveying heat which it possesses is due to the vapour of water which
it contains. By virtue of this moisture the winds do a good deal to
transfer heat from the tropical or superheated portion of the earth's
surface to the circumpolar or underheated realms. At first, the
relatively cool air which journeys toward the equator along the
surface of the sea constantly gains in heat, and in that process takes
up more and more water, for precisely the same reason that causes
anything to dry more rapidly in air which has been warmed next a fire.
The result is that before it begins to ascend in the tropical
updraught, being much moisture-laden, the atmosphere stores a good
deal of heat. As it rises, rarefies, and cools, the moisture descends
in the torrential rains which ordinarily fall when the sun is nearly
vertical in the tropical belt.

Here comes in a very interesting principle which is of importance in
understanding the nature of great storms, either the continuous storm
of the tropics or the local and irregular whirlings which occur in
various parts of the earth. When the moisture-laden air starts on its
upward journey from the earth it has, by virtue of the watery vapour
which it contains, a store of energy which becomes applied to
promoting the updraught. As it rises, the moisture in the air gathers
together or condenses, and in so doing parts with the heat which
caused it to evaporate from the ocean surface. For a given weight of
water, the amount of heat required to effect the evaporation is very
great; this we may roughly judge by observing what a continuous fire
is required to send a pint of water into the state of steam. This
energy, when it is released by the condensation of water into rain or
sn