ow, becomes again heat, and tends somewhat, as does the fire in the
chimney, to accelerate the upward passage of the air. The result is
that the water which ascends in the equatorial updraught becomes what
we may term fuel to promote this important element in the earth's
aerial circulation. Trades and counter trades would doubtless exist
but for the efficiency of this updraught, which is caused by the
condensation of watery vapour, but the movement would be much less
than it is.

WHIRLING STORMS.

In the region near the equator, or near the line of highest
temperature, which for various reasons does not exactly follow the
equator, there is, as we have noticed, a somewhat continuous uprushing
current where the air passes upward through an ascending chimney,
which in a way girdles the sea-covered part of the earth. In this
region the movements of the air are to a great extent under the
control of the great continuous updraught. As we go to the north and
south we enter realms where the air at the surface of the earth is, by
the heat which it acquires from contact with that surface, more or
less impelled upward; but there being no permanent updraught for its
escape, it from time to time breaks through the roof of cold air which
overlies it and makes a temporary channel of passage. Going polarward
from the equator, we first encounter these local and temporary
upcastings of the air near the margin of the tropical belt. In these
districts, at least over the warmer seas, during the time of the year
when it is midsummer, and in the regions where the trade winds are not
strong enough to sweep the warm and moisture-laden air down to the
equatorial belt, the upward tending strain of the atmosphere next the
earth often becomes so strong that the overlying air is displaced,
forming a channel through which the air swiftly passes. As the
moisture condenses in the way before noted, the energy set free serves
to accelerate the updraught, and a hurricane is begun. At first the
movement is small and of no great speed, but as the amount of air
tending upward is likely to be great, as is also the amount of
moisture which it contains, the aerial chimney is rapidly enlarged,
and the speed of the rising air increased. The atmosphere next the
surface of the sea flows in toward the channel of escape; its passage
is marked by winds which are blowing toward the centre. On the
periphery of the movement the particles move