674 Physiography. [ October, 
To take leave of metaphor, this amount of heat is expended in 
overcoming cohesion and tearing asunder the particles of water. 
The vapor particles thus formed, kept separate from each other - 
by heat, are carried by the wind to our shores; there the air in 
which they float is cooled; the heat is now insufficient to over- 
come the force of cohesion, and the water particles, no longer 
held apart, clash together, and as they do so they generate by the 
shock as much heat as was expended before in tearing them 
asunder. All the heat which disappeared—was rendered latent or 
hidden—when the vapor of water was raised from the Atlantic, is 
set free or rendered sensible when condensation takes place. For 
every nine pounds of weight of cloud formed in our skies, an 
amount of heat is set free sufficient to melt forty-five pounds of 
cast iron. 
A valuable lesson may rke learned from this behavior of water 
and water vapor. When the liquid water became gaseous vapor 
a certain amount of heat energy disappeared. But it was not 
destroyed. It was converted into another form of energy which 
we may call the energy of separation. The particles were forci- 
bly separated from one another, and a certain amount of energy 
was necessary to keep them apart. Presently, however, they 
clashed together again and the energy of separation was recon- 
verted into the energy of heat. The amount of heat given out 
was exactly equal to the amount of sun-heat absorbed. Day by 
day fresh experiment and observation make clearer this great law 
of nature : that by no means at our disposal can we either destroy 
or create energy. We may change it in a number of ways. We 
may convert chemical separation into electricity, this into mechani- 
cal motion, and mechanical motion into heat. But we can neither 
call into existence or put out of existence any portion of the 
energy of the universe, any more than we can call into existence 
or put out of existence any portion of the matter of the universe. 
One more fact must be noticed. Though the same amoùnt of 
heat is given out by the condensation of the aqueous vapor as 
was absorbed on the Atlantic during its formation, it is no longer 
useful in the same way. It does not possess the power of again 
converting water into water vapor. It has become degraded. It 
a is the same in amount, but different in value. The water which i 4 
turns a mill i is the same in amount whether it lies above or below 
water-wheel, PN it differs a in value. That above the 
