210 DOVE ON THE LAW OF STORMS. 
parallels of latitude, they would move towards g h if the space 
d bh were a vacuum; but if there be in this space air not in ~ 
movement, then the particles in 6, as they move towards d, will 
be continually coming in contact, in the space d 6 h, with par- 
ticles of air of inferior rotatory velocity, and thus their own east- 
ward velocity will be diminished. Thus the point J will move 
towards f instead of towards h; but the particles at a have near — 
them, on the side of 4, particles of originally equal rotatory ve- 
locity with their own; they move therefore as they would do 
in vacuo, i. ¢. towards g. Therefore if a 6 be a mass of air im- 
—- 
pelled from the south towards the north, then the direction in — 
which the storm is blowing will be much more southerly on its — 
eastern side than on its western side, where it will be more west- — 
erly, and thus there will arise a tendency to rotate in the sense 
S.E.N.W. This rotatory tendency would not be produced at 
all if there were no resisting mass in the space d bh; it will 
therefore be proportionate to the resistance thus opposed to | 
the westerly deflection of the storm, and the force of the ro- — 
tatory movement of the storm will be the greater the more the 
original direction of its path is preserved. In the zone of the © 
northern trade winds, the space d 6 his filled with air which 
is flowing from N.E. to S.W.; the resistance will here be the — 
greatest, so that the air in 6 may be so checked in its westward 
tendency, that it may preserve its direction towards d almost 
unaltered, whilst a@ tends toward g; the rotatory motion of the 
storm will therefore be the most violent, whilst at the same time 
its course will be rectilinear, and its breadth unaltered. But 
when it reaches the temperate zone there will be in the space 
d bh air which is already moving from 8.W. to N.E.; the re- 
sistance hitherto encountered at 4 will therefore be suddenly 
greatly diminished, or altogether removed ; and hence the direc- 
tion 6 d is suddenly changed into the direction b h, so that the 
storm is suddenly deflected almost at right angles, and at the 
same time its breadth increases rapidly from the cessation of the 
difference between the movements of the points in @ and the 
time to time had always come from the north-west, from which he concludes 
that they came from the mountains of Santa Martha, although all that is really 
indicated is that the islands are situated on the southern side of a rotating storm, 
in which the movement is in the opposite sense to that of the hands of a watch, 
or from east to west, which agrees perfectly with the observations referred to 
above. ‘The frontispiece of the sixth volume of Raynal’s work is a vivid pic- 
ture of a West Indian hurricane. 
