332 Bain. 



result of Joule's experiments that to raise one pound of water 

 one degree Fahrenheit, requires a quantity of heat sufficient 

 to raise one pound to a height of 772 feet; and the further 

 experimental fact, that to raise a pound of water from the 

 liquid to the vaporous state, requires 9G7 times as much heat 

 as is required to raise the same pound one degree Fahrenheit 

 in heat. 



The amount of water required to cover one hundred square 

 miles to a depth of one inch is, in volume — 



1760xl760x3x3xlOO-M2 



cubic feet, and as one cubic foot of water weighs 1000 oz., or 

 nearly 63 pounds, we have in weight — 



1 760 x 1760 x 3 X 3 x 8| x 62$ pounds, 



and to raise this weight of water 1° F., would require as much 

 heat as would suffice to raise to a height of one mile a weight of 



1 760 x 3 X 8i x 621 X 772 pounds ; 



while to vaporize the same weight of water would require 967 

 times as much heat. Thus we obtain a force sufficient to raise 

 a weight of — 



1760 x 3 X 17 x 135 x 193 X 967 pounds, 



(that is, nearly 1,020,000,000 tons), to the height of one 

 mile. 



Such is the amount of force, whose effects are exhibited in 

 a day's steady down-pour over a region of 100 square miles — 

 for instance, over about one-third of Middlesex. 



The same amount of water falling in the form of snow, 

 would represent a yet greater expenditure of force. " I have 

 seen," says Tyndall, " the wild stone-avalanches of the Alps, 

 which smoke and thunder down the declivities, with a vehe- 

 mence almost sufficient to stun the observer. I have also seen 

 snow-flakes descending so softly as not to hurt the fragile 

 spangles of which they were composed j yet to produce, from 

 aqueous vapom*, a quantity which a child could carry, of that 

 tender material, demands an exertion of energy competent to 

 gather up the shattered blocks of the largest stone-avalanche 

 I have ever seen, and pitch them to twice the height from 

 which they fell." 



But it is when we come to estimate the fall of rain as a 

 terrestrial phenomenon — as a process continually going on 

 over large regions of the earth's surface, as a process in which 

 energies exhibited over one region are expended, frequently, 

 over regions thousands of miles away — that we see the full 



