the shoulders, and carrying a basket
of provisions, suspended from his waist; and the frontispiece of the
"Philosophic sans Pretention" is a view of a flying-machine. In the
midst of a frame of light wood sits the operator, steadying himself with
one hand, and with the other fuming a cremaillere, which appears to
give a very quick rotatory movement to two glass globes revolving upon
a vertical axis. The friction of the globes is supposed to develop
electricity to which his power of ascending is ascribed.

To wings, however, aerial adventurers mostly adhered. The Marquis de
Racqueville flew from a window of his hotel, on the banks of the
Seine, and fell into a boat full of washerwomen on the river. All
these unfortunate attempts were lampooned, burlesqued on the stage, and
pursued with the mockery of the public.

Up to this time, therefore, the efforts of man to conquer the air had
miscarried. They were conducted on a wrong principle, the machinery
employed being heavier than the air itself But, even before the time
of Montgolfier, the principles of aerostation began to be recognised,
though nothing was actually done in the way of acting upon them. Thus,
in 1767, Professor Black, of Edinburgh, announced in his class that a
vessel, filled with hydrogen, would rise naturally in the air; but
he never made the experiment, regarding the fact as capable of being
employed only for amusement. Finally, Cavallo, in 1782, communicated
to the Royal Society of London the experiments he had made, and which
consisted in filling soap-bubbles with hydrogen. The bubbles rose in the
atmosphere, the gas which filled them being lighter than air.

Chapter III. The Theory of Balloons.

A certain proposition in physics, known as the "Principle of
Archimedes," runs to the following effect:--"Every body plunged into a
liquid loses a portion of its weight equal to the weight of the fluid
which it displaces." Everybody has verified this principle, and knows
that objects are much lighter in water than out of it; a body plunged
into water being acted upon by two forces--its own weight, which tends
to sink it, and resistance from below, which tends to bear it up. But
this principle applies to gas as well as to liquids--to air as well as
to water. When we weigh a body in the air, we do not find its absolute
weight, but that weight minus the weight of the air which the body
displaces. In order to know the exact weight of an object, it would be