. A silken bag from lute-string silk, about
thirteen feet in diameter, and of a globular shape, was constructed by
the Messrs. Roberts, under the superintendence of M. Charles, professor
of experimental philosophy; and, to render the bag impervious to the
gas--a very essential object in balloon manufacture--it was covered with
a varnish composed of gum elastic dissolved in spirits of turpentine. It
had but one aperture, like the neck of a bottle, into which was fastened
the stop-cock for the convenience of introducing and stopping-off the
gas. It was constructed and inflated near the Place of Victories, in
August, 1783, and after being inflated, which was then no easy task,
occupying several days, it was removed on the morning of the 27th of
that month, before daylight, to the Camp of Mars (two miles distant),
the place appointed for its ascent. About five o'clock in the afternoon,
it was released from its fastenings, and rose, in the presence of some
hundred thousands of applauding spectators, to a height upward of 3000
feet; and, after remaining in the atmosphere for three-quarters of an
hour, descended in a field near Gonesse, a village about fifteen miles
distant from the Camp of Mars. This marks another important era in the
history of aeronautics. The hydrogen-gas balloon, in the first place, is
attended with less risk than the Montgolfiers' balloon, which requires
the dangerous presence of a fire to preserve the air in a sufficiently
rarified state; and, in the second place, it has a much greater
ascending power than rarified air balloons of the same size, in
consequence of its superior lightness.

M. Charles and the two Messrs. Roberts now resolved to undertake an
aerial excursion in a balloon of this description. With this view, the
Messrs. Roberts formed one of silk, varnished with gum elastic, of a
spherical shape, 27 feet in diameter, with a car suspended from it by
several cords, which were fastened to a net drawn over the upper part of
the balloon. To prevent the danger which might arise from the expansion
of the gas under a diminished pressure of the atmosphere in the higher
regions, the balloon was furnished with a valve, to permit the free
discharge of gas, as occasion might require. The hydrogen gas with which
it was filled was 5-1/4 lighter than common air, and the filling lasted
several days. On December 17, 1783, M. Charles and one of the Roberts
made their ascent from the garden of the Tuilleries, an