, and varnished with a certain composition which renders the
balloon air-tight. The car in which we will travel is made of
wicker-work, for that is both light and strong, and it is suspended
from a net-work of strong cord which covers the whole balloon. It
would not do, you know, to attach a cord to any particular part of the
silk, for that would tear it. In the top of the balloon is a valve,
and a cord from it comes down into the car. This valve is to be pulled
open when we wish to come down towards the earth. The gas then
escapes, and of course the balloon descends. In the car are bags of
sand, and these are to be emptied out when we think we are too heavy
for the balloon, and are either coming down too fast or are not as
high as we wish to go. Relieved of the weight of a bag, the balloon
rises.

Sand is used because it can be emptied out and will not injure anybody
in its descent. It would be rather dangerous, if ballooning were a
common thing, for the aeronauts to throw out stones and old iron, such
as are used for the ballast of a ship. If you ever feel a shower of
sand coming down upon you through the air, look up, and you will
probably see a balloon--that is, if you do not get some of the sand in
your eyes.

The gas with which our balloon is to be filled is hydrogen gas; but I
think we will not use the pure hydrogen, for it is troublesome and
expensive to produce. We will get permission of the city gas
authorities to take gas from one of their pipes.

That will carry us up very well indeed. When the balloon is nearly
full--we never fill it entirely, for the gas expands when it rises
into lighter air, and the balloon would explode if we did not leave
room for this expansion--it is almost as round as a ball, and swells
out proudly, struggling and pulling at the ropes which confine it to
the ground.

[Illustration]

Now we have but to attach the car, get in, and cut loose. But we are
going to be very careful on this trip, and so we will attach a
parachute to the balloon. I hope we may not use it, but it may save us
in case of an accident. This is the manner in which the parachute will
hang from the bottom of the car.

It resembles, you see, a closed umbrella without a handle, and it has
cords at the bottom, to which a car is attached. If we wish to come
down by means of this contrivance, we must descend from the car of the
balloon to that of the parachute, and then we must unfasten the rope
which attaches u