lower parts; this becomes heated in its turn, and is
continually replaced; thus, an extremely rapid current of gas
is established in the pipes and in the spiral, which issues
from the balloon and then returns to it, and is heated over
again, incessantly.

"Now, the cases increase 1/480 of their volume for each
degree of heat applied. If, then, I force the temperature
18 degrees, the hydrogen of the balloon will dilate 18/480 or
1614 cubic feet, and will, therefore, displace 1614 more
cubic feet of air, which will increase its ascensional power
by 160 pounds. This is equivalent to throwing out that
weight of ballast. If I augment the temperature by 180
degrees, the gas will dilate 180/480 and will displace 16,740
cubic feet more, and its ascensional force will be augmented
by 1,600 pounds.

"Thus, you see, gentlemen, that I can easily effect
very considerable changes of equilibrium. The volume of
the balloon has been calculated in such manner that, when
half inflated, it displaces a weight of air exactly equal to
that of the envelope containing the hydrogen gas, and of
the car occupied by the passengers, and all its apparatus
and accessories. At this point of inflation, it is in exact
equilibrium with the air, and neither mounts nor descends.

"In order, then, to effect an ascent, I give the gas a
temperature superior to the temperature of the surrounding
air by means of my cylinder. By this excess of heat
it obtains a larger distention, and inflates the balloon