come down, he lets the gas escape by the valve at the roof of the
balloon. This valve is worked by means of a spring, having a long
rope attached to it, which hangs down through the neck to the
car, where the aeronaut sits.

The operation of inflating a balloon with pure hydrogen is
represented in the engraving on the next page.

Shavings of iron and zinc, water, and sulphuric acid, occupy a
number of casks, which communicate, by means of tubes, with a
central cask, which is open at the bottom, and is plunged in a
copper full of water. The gas is produced by the action of the
water and the sulphuric acid upon the zinc and the iron this is
hydrogen mixed with sulphuric acid. In passing through the
central copper, or vat, full of water, the gas throws off all
impurities, and comes, unalloyed with any other matter, into the
balloon by a long tube, leading from the central vats. In order
to facilitate the entrance of the gas into the balloon two long
poles are erected. These are furnished with pulleys, through
which a rope, attached also to a ring at the top of the balloon,
passes. By means of this contrivance the balloon can be at once
lightly raised from the ground, and the gas tubes easily joined
to it. When it is half full it is no longer necessary to suspend
the balloon; on the contrary, it has to be secured, lest it
should fly off. A number of men hold it back by ropes; but as
the force of ascension is every moment increasing, the work of
restraining the balloon is most difficult and exciting. At
length, all preparations being complete, the car is suspended,
the aeronaut takes his seat, the words "Let go all!" are shouted,
and away goes the silken globe into space.