1874.| The Iowa and Illinois Tornado. 387 
1. Pressure per square foot 41°7 lbs. Velocity of wind, 
g1°3 miles per hour. 
Pressure, 71°4 lbs. Velocity, 119°5 miles. 
Pressure, 56°8 Ibs. Velocity, 106°6 miles. 
f Eressure, 234°3 lbs. Velocity, 21675 miles. 
Pressure, 51 lbs. Velocity, r00’9 miles. 
Pressure, 46°9 lbs. Velocity, 96°8 miles. 
Pressure, 107°4 lbs. Velocity, 146°6 miles. 
Only one of these buildings was not, in addition to being 
pushed from its foundation, carried away, ViZ., case 4. It, 
however, was pushed through a dense mass of tough rub- 
bish, and its sides were bent from the perpendicular. 
Owing to its small surface and great weight, the force of the 
wind exceeded the minimum required to push the building 
from its foundations less in this case than in any of the 
others. Hence we have the great velocity of 216°4 miles 
per hour, or of 317°4 feet per second, in a horizontal direc- 
tion. It is also probable that in this case the kinetic friction 
was greater than the static, and that it increased every 
moment until the building came to a stand. 
The Amount of the Precipitation.—It was impossible to ob- 
tain more than generalities on this head. There were no 
rain-gauge measurements, so far as I could learn. At 
Davenport, however, a few miles from where damage was 
done on the Mississippi, there fell, on May 22, 1°35 inches, 
as shown by the Signal Service Reports. From the descrip- 
tion of the rain to the north of the funnel, in Washington 
County, a greater quantity than this must have fallen at 
many places. It is not, therefore, likely that we shall over- 
estimate the amount when we assume that 2 inches of rain 
fell over an area 10 miles in width. Since the tornado tra- 
velled 30 miles per hour, this gives a rainfall per minute of— 
2 X (10 X 2) X 3,097,600 X9 X 144 _ 
1728 
Tornado Dynamics.—A cubic foot of water weighs ro000 
ounces. The weight of water which fell per minute was 
therefore— 
23,232,000 X 1000 
16 
It is not, probably, an exaggeration to assume that this mass 
of water fell, on an average, 6 miles or more. This gives a 
horse-power oie 
14,522,000,000 X (6 X 5280) _ 
33,000 Hs 
generated by the falling water. 
WOYEY 
23,232, 000 cubic feer. 
=1,452,000,000 lbs. 
I,393,920,000, 
