tly.

These considerations tended to turn the minds of those interested
in aerostation to consideration of the hydrogen balloon evolved by
Professor Charles. Certain improvements had been made by Charles
since his first construction; he employed rubber-coated silk in the
construction of a balloon of 30 feet diameter, and provided a net for
distributing the pressure uniformly over the surface of the envelope;
this net covered the top half of the balloon, and from its lower edge
dependent ropes hung to join on a wooden ring, from which the car of
the balloon was suspended--apart from the extension of the net so as to
cover in the whole of the envelope, the spherical balloon of to-day is
virtually identical with that of Charles in its method of construction.
He introduced the valve at the top of the balloon, by which escape of
gas could be controlled, operating his valve by means of ropes which
depended to the car of the balloon, and he also inserted a tube, of
about 7 inches diameter, at the bottom of the balloon, not only for
purposes of inflation, but also to provide a means of escape for gas in
case of expansion due to atmospheric conditions.

Sulphuric acid and iron filings were used by Charles for filling his
balloon, which required three days and three nights for the generation
of its 14,000 cubic feet of hydrogen gas. The inflation was completed on
December 1st, 1783, and the fittings carried included a barometer and a
grapnel form of anchor. In addition to this, Charles provided the first
'ballon sonde' in the form of a small pilot balloon which he handed to
Montgolfier to launch before his own ascent, in order to determine the
direction and velocity of the wind. It was a graceful compliment to his
rival, and indicated that, although they were both working to the one
end, their rivalry was not a matter of bitterness.

Ascending on December 1st, 1783, Charles took with him one of the
brothers Robert, and with him made the record journey up to that date,
covering a period of three and three-quarter hours, in which time they
journeyed some forty miles. Robert then landed, and Charles ascended
again alone, reaching such a height as to feel the effects of the
rarefaction of the air, this very largely due to the rapidity of his
ascent. Opening the valve at the top of the balloon, he descended
thirty-five minutes after leaving Robert behind, and came to earth a few
miles from the point of the first descent. His discomf