38 AERIAL NAVIGATION. 
clouds of vapor and smoke floated readily in the air, 
they conceived the idea of substituting these for hydro- 
gen. Since the publication of Franklin’s investigations 
on atmospheric electricity in 1752, the idea seemed to 
gain currency that electricity was an important agent in 
causing clouds to float in mid-air, and it was this that 
the Montgolfiers wished to utilize. A paper bag, with 
a capacity of about forty cubic feet, was held, the open- 
ing downward, over a fire of chopped straw and wool. It 
was quickly inflated and carried to the ceiling of the 
room. The experiment was soon repeated on a larger 
scale and a successful public exhibition was given at the 
village of Annonay on the fifth of June, 1783. The 
Montgolfiers seem to have regarded their success as due 
to the discovery of a new kind of gas, generated by the 
burning of straw and wool, rather that to the rarefaction 
of the air by heating it. 
The news of the success at Annonay soon reached 
Paris, where a subscription was at once made up for the 
purpose of defraying the expense of constructing a bal- 
loon. The direction of the work was intrusted to Charles, 
a physicist, who had already become well Known through 
‘his investigations in regard to the influence of tempera- 
ture in modifying the density of gases. Charles at once 
comprehended the true principle underlying the success 
of the Montgolfiers, but decided to use hydrogen, con- 
fining it in a spherical bag, not of paper, but of thin silk 
varnished with india-rubber. The diameter of this bal- 
loon was twelve feet. If filled with pure hydrogen, its 
ascensive force would therefore have been a little over 
sixty pounds. On account of the defective method of 
preparing hydrogen at that time employed, much diffi- 
culty was experienced in inflating the balloon, but an 
ascent was successfully made on theafternoon of August 
27, 1783, from the Champ de Mars, an open space on the 
outskirts of Paris, south of theriver Seine. It remained 
