in diameter' and 2,250 cubic feet in capacity. Of such
a balloon, the accessories--the skin, the network, the car--would weigh
about 335 lbs.

To find out the height at which he has arrived, the aeronaut consults
his barometer. We know that it is the pressure of the air upon the cup
of the barometer that raises the mercury in the tube. The heavier the
air is, the higher is the barometer. At the level of the sea the column
of mercury stands at 32 inches; at 3,250 feet--the air being at this
elevation lighter--the mercury stands at 28 inches; at 6,500 feet above
sea level it stands at 25 inches; at 10,000 feet it falls to 22 inches;
at 20,000 feet to 15 inches. These, however, are merely the theoretic
results, and are subject to some slight variation, according to
locality, &c.

Sometimes the aeronaut makes his descent by means of the parachute,
a separate and distinct contrivance. If, from any cause, it appears
impracticable to effect a descent from the balloon itself, the parachute
may be of the greatest service to the voyager at the present day it is
chiefly used to astonish the public, by showing them the spectacle of
a man who, from a great elevation in the air, precipitates himself into
space, not to escape dangers which threaten him in his balloon, but
simply to exhibit his courage and skill. Nevertheless, parachutes are
often of great actual use, and aeronauts frequently attach them to their
balloons as a precautionary measure before setting out on an aerial
excursion.

The shape of a parachute, shown on the previous page, very much
resembles that of the well-known all serviceable umbrella. The strips of
silk of which it is formed are sewn together, and are bound at the top
around a circular piece of wood. A number of cords, stretching away from
this piece of wood, support the car in which the aeronaut is carried. At
the summit is contrived an opening, which permits the air compressed
by the rapidity of the descent to escape without causing damage to the
parachute from the stress to which it is subjected.

The rapidity of the descent is arrested by the large surface which the
parachute presents to the air. When the aeronaut wishes to descend by
the parachute, all that is required is, after he has slipped down from
the car of the balloon to that of the parachute, to loosen the rope
which binds the latter to the former, which is done by means of a
pulley. In an instant the aeronaut is launched into space with a