. 
¥874.| The Iowa and Illinois Tornado. 389 
through a space of 481 feet. The power, therefore, gene- 
rated by this mass of air moving with the given velocity 
amounts to— 
5330,020,875,922 x 481 
33,000 
The latent heat of evaporation amounts to about 1000’. 
Consequently the condensation of 1,452,000,000 lbs. of vapour 
is accompanied by the evolution of 1,452,000,000 X 1000 ca- 
lorics or pound degrees of heat. The specific thermal capa- 
city of air, as compared with water, is as 0°237to 1. The 
number of degrees, therefore, which this amount of heat 
would raise 1 lb. of air is— 
1,452,000,000,000 X Baa 6,126,582,278,481 degrees. 
= 77,089,092,161,166 horse-power. 
But the pressure remaining the same air expands zi; part of 
its volume for every accretion of 1 degree of temperature. 
This amount of heat would therefore expand 1 Ib. of air 
6,126,582,278,481 
491 
air at 30 inches pressure, 60° temperature, and having a re- 
lative humidity of 65 per cent, weighs 538°6 grains. A 
pound of such air, therefore, occupies— 
7000 
538°6 
A pound of air, therefore, in doubling its volume must— 
the pressure remaining 15 lbs. per square inch—raise a 
weight 13 X 144 X 15 =28,080 lbs. through 1 foot. The total 
amount of work, therefore, performed by 1 lb. of air, while 
expanding—under a pressure of 15 lbs. per square inch—to 
12,477,764,315 times its original bulk, is 12,477,764,315 x 
28,080 foot-pounds. This amount of work accomplished 
per minute demands— 
12,477,704,315 x 28,080 
33,000 
We thus see that the power generated by the condensation 
of the amount of vapour estimated as having been precipi- 
tated is much less than that calculated to have been produced 
by the velocity of the centripetal winds. Theoretically, this 
power should be diminished by the amount of expansion 
counteracted by the removal of so large a mass of vapour. 
Practically, however, it seems probable that this removal of 
vapour, while increasing the specific gravity of the air, serves 
rather to increase the rarefaction when taking place with 
great rapidity. 
VOL, IV. (N.S.) 20 
= 12,477,764,315 times. A cubic foot of 
=12-99—13 Cubic feet very nearly. 
= 10,617,443,089°8 horse-power. 
