Mr Joseph J. Murphy on Revolving Storms. 237 
of rarefaction will be deflected toward W, that from W 
towards §, that from S towards H, and that from E towards 
N. As these deflections are all in the same direction round 
a circle, they combine and produce a vortex. All these 
directions are, of course, reversed in the opposite hemi- 
spheres. The rotation of the storm ts in the opposite direction 
to the deflection, or 
what Dové calls the N 
gyration, of the sepa- 
rate winds, as will 
be obvious from the 
diagram, where the 
cross represents the 
converging paths 
which the winds 
would take in the 
absence of any de- 
flecting force, and 
the arrows the di- 
rections in which 
they are deflected. Ss 
Of course it is not 
accurate to draw the arrows straight. Were there no friction, 
the velocity would be regulated by the law of the conserva- 
tion of areas, and its tangential component in any part of 
the cyclone would be inversely as the distance from the 
centre. Cyclones never cross the equator, and are never 
formed on it, because the deflecting force is in opposite direc- 
tions in opposite hemispheres, and null on the equator. 
Such are the forces that move the cyclone. But the 
manner in which it is originally set agoing has not hitherto 
been fully explained. The following explanation is founded 
on that contained in Dové’s recently translated ‘ Law of 
Storms,” and is partly identical with it :— 
Cyclones are local and temporary phenomena: they occur 
chiefly in, 1st, The West Indian Seas ; 2d,.The Indian Ocean 
west of India ; 3d, The South Indian Ocean ; 4th, The Chinese 
Sea; and dth, The Bay of Bengal: in all these they occur 
oftenest in the end of summer, except in the last, where 
they are most frequent twice a year, at the change of the 
NEW SERIFS.—VOL. XVIII. NO, 11.—OcTOBER 1863. 2H 
W E 
