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under an exhausted receiver, or from a very rapid one con- 
tinued for a short time, as when ether and solid carbonic acid 
are employed to abstract the heat of water. The time 
occupied by the descent of a hailstone being necessarily 
short, we are compelled to account for its perfect solidi- 
fication by the rapid evaporation to which it has been 
subjected. It is obvious that hailstones of class II, must 
have been subjected to a different evaporating condition 
from those of the other classes, and it is from these I think 
we best learn the true explanation of the phenomena of 
hailstorms. 
Were a solid body projected from the clouds to the earth, 
it would displace the atmosphere through the entire length 
of its path, causing a condensation on either side, and in 
front of it. Were its velocity equal to that of electricity, 
and its base a hundred miles square, there is no difficulty in 
conceiving such an amount of condensation on either side 
of its path as is adequate to the production of heat enough 
to cause light, its path from the cloud to the earth being a 
temporary vacuum which becomes filled from above as the 
solid descends. 
The electric tension of a storm cloud continues to increase 
until it is able to overcome the resistance to discharge offered 
by the mass of air between itself and the earth. As soon as 
this degree of tension is reached, discharge takes place, and 
now no known force can resist the electric force, but its 
onward path must continue until equilibrium is restored by 
some body in an opposite electric condition. But, although 
ineffectually, the air offers resistance at every inch of the 
progress made by the electricity, and the condition of its 
progress is the overcoming of atmospheric resistance by a 
removal from its path of the opposing matter. Familiar 
illustrations of this are the fusion and dispersion in all 
directions of small metallic wires, stones, &c, which offer 
