312 



HISTORY OF SCIENCE. 



smoke should fill the balloon. The Montgolfiers at this time erro- 

 neously imagined that the ascensive power was due to the smoke, 

 whereas in reality it was the expansion of the air within the balloon 

 occasioned by the heat that produced the effect. The first aerial 

 voyage was made by Pilatre de Rozier and the Marquis d'Arlandes on 

 the 2ist of November, 1783, in the Montgolfier (or fire) balloon repre- 

 sented in Fig. 150. Ten days afterwards two daring experimenters 

 made at Paris the first voyage in which a balloon filled with hydrogen 

 gas was used. Balloon ascents after that became comparatively fre- 

 quent. 



The most ingenious and persevering attempts have been made to 

 find some method of propelling or of guiding balloons through the 

 air. None have succeeded ; chiefly because a balloon does not, like 

 a bird, move through the air, it merely moves with the air. There 

 are, however, many persons who still believe in the practicability of 

 directing the course of balloons. 



FIG. 151. 



