34 W. Ferrel—Cyclones, Tornadoes and Waterspouts. 
eastward motions in the higher latitudes increase with increase 
of altitude, but nearer the equator the westward motions 
decrease with increase of altitude and at a certain altitude van- 
ish and become eastward motions. i 
The deflecting force depending upon the earth’s rotation 1s 
such that if the air on the parallel of 45° has a velocity of 54 
miles per hour, it gives rise to a gradient of pressure, increasing 
to the right of the direction of motions in the northern hem1- 
sphere, and the contrary in the southern, of 0°1 inch of mercury 
in the distance of one degree of a great circle of the earth. 
This force, and consequently the gradient, is as the velocity and 
the sine of the latitude, and hence it is a maximum at the pole 
and decreases toward and vanishes at the equator. The east- 
t 
ward motion, therefore, in the middle and higher latitudes gives 
The regularity of the general motions of the atmosphere and 
of the gradients depending upon them, is very much interfered 
with by irregularities in the distribution of the earth’s tempera- 
ture arising from ocean currents, and from irregularities of 
understand the theory of cyclones, tornadoes, etc. 
_ Oyclones.—Cyclones arise from more local disturbances of 
tem i 
: ’ 
eart 
other means exactly equals the amount received, and hence 
there cannot be uniformity of temperature even on the same 
