wx 
X THE GEELONG NATURALIST ` 
shown by a calculation, based on Joules’ experiments, that to 
evaporate a quantity of water sufficient to cover an area of 
100 miles to the depth of 1 inch, would require as much heat 
as is produced by the combustion of half a million tons of.coal ; 
and further, the amount of force of which such a consumption 
of heat is equivalent, corresponds to that which would be 
re required to raise a weight of upwards of 1000 millions of 
tons to a height of one mile. i 
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. Yet to pro- 
duce from aqueous vapour 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, not 
merely over 100 square miles, but asa 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 significance of the drop of 
rain. We may form some idea of the force involved, when 
we consider that all the coal which. could be raised by man 
from the earth in thousands of years would not give out heat 
enough to produce the earth's rain supply for one single year. 
I have these figures on the authority of the late R. A. Proctor, 
a man whoseauthority on scientific subjects is unquestionable. 
In connection with this idea of the mechanical force in- 
volved in rain, I would like—although it is somewhat of a 
digression —to carry the idea a little further, and enquire what 
use is made by man of this power. When rain reaches the 
earth, all the tremendous force which we have just seen is 
required to produce it is not spent, for it does not all fall to 
the sea level; some of it is collected on mountain ranges and 
high regions—watersheds, we call them—and thence finds its 
way by babbling brook or mountain torrent into the rivers, 
and there, in larger volume, rushes onward to the sea. Has 
adequate use been made in the past, is it being made in the 
present, or will it be made in the future by mankind of this 
never-failing supply of energy—NW ater Power ? 
( To be Continued.) 
