66 On the Rotary Action of Storms. 
rotary is by far the most violent, and has an uniform direction of 
revolution, being from right to left if the storm is in the northern 
hemisphere, and the reverse if it is in the southern hemisphere. 
That is to say, on our side of the equator the rotation is about 
the centre through the points of compass, in the order of N. W. 
S. E., or contrary to the movement of the hands of a watch lying 
on its back; and south of the equator the rotation is through the 
points in the order of N. BE. S. W., or conformable to that of the 
hands of a watch. 
These propositions, although authorized by induction, have 
encountered doubts or gained a feeble faith in many minds, for 
the want of a good cause to assign for the production of the 
alleged phenomena. Hence the occurrence of rotary storms, and 
the uniformity of direction of revolution, have been too readily 
attributed to mere accident; and the notion that a whirlwind, 
once started by mere chance, contains the elements of growth 
and stability of motion, has been too easily admitted. An active 
whirlwind, great or small, undergoes a constant change of sub- 
stance. As the central portions waste into the ascending column, 
supplies from the adjacent tranquil air must be drawn into the 
vortex and set in motion; and if the fresh air is neutral to the 
circular movement and must acquire velocity from the whirling 
mass itself, then since “action and reaction are equal and in op- 
posite directions,” the whirling mass itself must lose just so much 
velocity as the fresh supply gains. By such a process the forces 
of the whirlwind would be rapidly exhausted, and its existence 
must speedily cease. A stable source of momentum, adapted to 
originate and sustain the uniform rotary movement, is still re- 
quired : and it is now proposed to develop such a source of mo- 
mentum in the forces generated by the earth’s diurnal revo- 
lution. 
The velocity of the earth’s surface in the daily revolution being 
at the equator more than one thousand miles an hour, in latitude 
60° half as much, at the pole nothing, and varying in interme- 
diate places as their perpendicular distances from the earth’s axis, 
and the atmosphere near the ground every where taking in part 
or wholly the motion of the surface it rests on, important conse- 
quences upon aerial currents must follow. A body of air set in 
motion from the equator northward maintains the equatorial east- 
ward velocity, and when it passes over regions of slower rotation 
