THE OCEAN IN WHICH WE LIVE. 
93 
ing against it. By means of broom-wire the board 
was attached to a small spring balance fastened upon 
a horizontal rest. This indicated the pressure of the 
wind in pounds to the square foot. 
The rate at which the air moves is its velocity, and 
is expressed in miles per hour. It is determined with 
an anemometer (wind- 
measure). By means of 
the table it was not diffi¬ 
cult to learn the velocity 
from the pressure. Mul¬ 
tiply the number of 
pounds of pressure by 
two hundred, and the 
square root of the prod¬ 
uct will equal the veloc¬ 
ity. I found that the 
pressure was greater on 
high buildings or on a 
hill than in a valley. The 
wind is also stronger on 
the ocean or open prairie. 
The air seldom moves at uniform rate, but in 
waves or gusts. It seems to come in great waves, 
with little waves upon them, as we often see upon 
the water. 
Gentle breeze. 4 oz. 7 miles per hour. 
Light wind. 1 lb. 14 “ 
Stiff breeze. 2 lbs. 20 “ “ 
Gale. 8 “ 40 
Heavy storm. 18 “ 60 
Tornado. 50 to 200 lbs. 100 to 200 “ “ 
Fig. 51.—Anemometer. Wind 
blowing into the cups whirls 
them around. The velocity 
is indicated by the hand on 
the dial. 
