slowly, but as they win
their way toward the centre they travel with accelerating velocity. On
the principle which determines the whirling movement of the water
escaping through a hole in the bottom of a basin, the particles of the
air do not move on straight lines toward the centre, but journey in
spiral paths, at first along the surface, and then ascending.

We have noted the fact that in a basin of water the direction of the
whirling is what we may term accidental--that is, dependent on
conditions so slight that they elude our observation--but in
hurricanes a certain fact determines in an arbitrary way the direction
in which the spin shall take place. As soon as such a movement of the
air attains any considerable diameter, although in its beginning it
may have spun in a direction brought about by local accidents, it will
be affected by the diverse rates of travel, by virtue of the earth's
rotation, of the air on its equatorial and polar sides. On the
equatorial side this air is moving more rapidly than it is on the
polar side. By observing the water passing from a basin this
principle, with a few experiments, can be made plain. The result is to
cause these great whirlwinds of the hurricanes of higher latitudes to
whirl round from right to left in the northern hemisphere and in the
reverse way in the southern. The general system of the air currents
still further affects these, as other whirling storms, by driving
their centres or chimneys over the surface of the earth. The principle
on which this is done may be readily understood by observing how the
air shaft above a chimney, through which we may observe the smoke to
rise during a time of calm, is drawn off to one side by the slight
current which exists even when we feel no wind; it may also be
discerned in the little dust whirls which form in the streets on a
summer day when the air is not much disturbed. While they spin they
move on in the direction of the air drift. In this way a hurricane
originating in the Gulf of Mexico may gradually journey under the
influence of the counter trades across the Antilles, or over southern
Florida, and thence pursue a devious northerly course, generally near
the Atlantic coast and in the path of the Gulf Stream, until it has
travelled a thousand miles or more toward the North Atlantic. The
farther it goes northward the less effectively it is fed with warm and
moisture-laden air, the feebler its movement becomes, until at length
i