116 
HAROLD’S DISCUSSIONS. 
Investigation has proved that winds are changed 
from their direction by another force, due to the 
spherical shape of the earth combined with its rota¬ 
tion. A French mathematician in 1837 computed 
that a freely moving body on the surface of a rotat¬ 
ing sphere will, or ought to, move toward the right of 
its course and describe a circle, and that the faster it 
moves the greater will be the circle it describes. 
The eminent French experimenter, Foucault, in 
1851, suspended a long, heavy pendulum so that it 
could oscillate freely in any direction. He found 
that if the pendulum was started in a certain plane, 
it gradually oscillated more and more toward the 
right, north of the equator, until it completed the 
circle. The same experiment proved that it would 
move toward the left in the southern hemisphere. 
This can be tested by almost any one. The pendu¬ 
lum should be at least twenty-five feet long in order 
to make the movement evident. 
Five years after Foucault’s demonstration Mr. 
Ferrel applied this idea to the air currents and worked 
out his theory of the winds, which is now generally 
accepted. 
This principle may be restated thus: If the ob¬ 
server stands with his back to the wind, the currents 
will gradually curve to the right, in the northern 
hemisphere, no matter wdiich way the wind blows. 
Thus a north wind would not remain north, but 
would gradually veer toward the west, becoming first 
a northeast wind, then east, then southeast, and so 
on, completing the circle. A south wind would not 
