324 Relations of Storms to Contiguous Winds. 
tendency to rotation is commonly shown in some degree, in the 
successive phenomena and phases of the trade winds, in the re- 
gion near St. Helena and in other tracts of ocean which are ex- 
empt from severe storms. In some other regions, as in the west- 
ern portions of an oceanic basin in the tropical latitudes, the In- 
dian ocean near Mauritius, and in the south Pacific from the Socie- 
ty to the Navigator’s Islands, this tendency to a vorticular rotation 
appears to be directly promoted by local or specific causes, the 
most -efficient of which are found in the actual courses of the 
several local winds or aérial currents, either in the same plane of 
the horizon, or at different elevations. Thus, Mr. Thom main- 
tains that the hurricanes of the Indian Ocean are due to the op- 
posite or tangential action of the N. W. and S. E. monsoons on 
each other in that sea; and I apprehend that the earliest activity 
and violence of the iitertneipicnl hurricanes may often be rightly 
explained in this manner.* 
This, however, cannot ane: explain the sisfonnitet of the 
direction of rotation, nor the continued: activity of the storms in 
their progress to other regions and in higher latitudes, where their 
greatest violence is sometimes developed.t | Nor is the extraneous 
and tangential force of contiguous winds or currents at all neces 
sary to the continued activity of the storm, when once the fall 
of the barometer and the involute vortical movement has been 
produced; for the pressure of the external atmosphere, around 
the basin of the storm, constantly aids or impels the involute 
movement at the earth’s surface, and may be sufficient to mail- 
tain the existing vortical ae ad be seen in the case of a 
common vortex or whirlwind. whe 
_ We have seen that the two Cuba storms, as’ ose as the Mexi- 
can Northers, have appeared to come from the contiguous border 
of the Pacific ocean. Now, are there any peculiarities in the 
winds and aerial currents of those regions which may serve to in- 
duce or support a leftwise rotation invextensive portions of. 
lower atmosphere, while moving on or-near the earth’s surface? 
™~ 
I apprehend there are such eRe e mécogiente: tole xteeatty 
chnetant and. rene influence. 
ae fee 
. ‘In ‘such cases a suppose that ex . of these different 0 or ri 
winds ma may coale esce in a vast. erie: oer of pursuing their 
, Stratiform without ‘interference of: 
