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of Atmospherical Phenomena. 37 
the higher regions of the atmosphere in the tropics the air is not 
always flowing regularly from S. W. to N. E., but that this usual 
and regular direction is sometimes interrupted by currents from 
east to west. I think I have indicated the probable cause of such 
anomalous currents in the above described barometric relations of 
the region of the monsoons compared with that of the trades. 
If we suppose the upper portions of the air ascending over Asia 
and Africa to flow off laterally, and if this takes place suddenly, 
it will check the course of the upper or counter current above the 
trade wind, and force it to break into the lower current. An east 
wind coming into a S. W. current must necessarily oceasion a ro- 
tatory movement, turning in the opposite direction to the hands of a 
watch. A rotatory storm moving from S. E. to N. W. in the lower 
‘current or trade, would in this view be the result of the encounter 
of two masses of air impelled towards each other at many places 
in succession, the further course of the rotation (originating pri- 
marily in this manner) being that described by me in il i 
memoir “On the Law of Storms,” translated in the Scientific 
Memoirs, vol. iii, art. 7. Thus it happens that the West India 
hurricanes and the Chinese typhoons occur near the lateral con- 
nes on either side of the great region of atmospheric expansion, 
the typhoons being probably occasioned by the direct pressure of 
the air from the region of the trade winds over the Pacific into 
the more expanded air of the monsoon region, and being distinct 
from the storms appropriately called by the Portuguese “ ‘Tempo- 
rales,” which accompany the outburst of the monsoon when the 
direction of the wind isreversed. The fact of the rotatory storms 
being of much more rare occurrence in the South Atlantic Ocean 
the Old World presents all the characteristic marks of the region 
of calms, being a centre towards which all adjacent masses of 
air are drawn. Hence there is no complete sub-tropical zone, in 
the sense of a zone encompassing the globe. The region over 
which the heated air ascends does not therefore move up and 
down, or north and south, parallel with the sun’s change of de- 
clination, but has rather a kind of oscillatory movement, in which 
the West Indies represent the fixed point, and the greatest ampli- 
