Mr Joseph J. Murphy on Revolving Storms. 239 
by the meeting of the N.H. trade wind and the 8.W. mon- 
soon; this takes place over the Chinese Sea in summer, 
and over the Bay of Bengal after the equinoxes. 
Besides their rotation, cyclones have a motion of transla- 
tion, and this, within the tropics, is always towards W. ; 
sometimes N.W., sometimes §.W., but always W. In the 
Chinese Sea this is contrary to the prevalent wind at the 
time they occur, which is the §8.W. monsoon. This has 
not hitherto been accounted for. It is probably due to the 
fact that the rotation of the earth round an axis drawn per- 
pendicular to its surface, as illustrated by Foucault's pen- 
dulum, varies as the sine of the latitude, and is consequently 
most rapid in the highest latitude; so that the higher the 
latitude from which the air in any part of a cyclone is 
drawn, the more it will have been deflected, and the greater 
will be its centrifugal force. Now, a glance at the diagram 
will show that the air on the west side of every cyclone comes 
from a higher latitude, and that on the east from a lower; 
the former has consequently the most centrifugal force, and 
determines the motion of the whole cyclone towards west. 
It might be supposed that the motion in question is a 
resultant of the motions of the upper and lower currents 
of air, which in the tropical regions are usually different. 
This, however, could scarcely be reconciled with the fact 
that in the West Indian region the lower current (the trade 
wind) is from N.E., while in that of the Chinese Sea, 
during the prevalence of cyclones, it is from 8.W. Little 
is known of the direction of the upper current in either 
case; 1t is probably rather fluctuating, but more nearly 
opposed to the lower currents than coincident with them. 
It appears probable that the resultant of the motions of the 
upper and lower currents in the West Indian region is more 
likely to be in the opposite direction to the same resultant 
in the Indian and Chinese region, than in nearly the same 
direction. 
The cyclones of the West Indian Sea and South Indian 
Ocean, besides their motion to west, generally move towards 
the Pole. On reaching a latitude of about 28°, they lose 
much of their force, widen rapidly, and, losing their motion 
towards west, drift eastward and Pole-ward, with nearly the 
