100 THE APPLICATIONS OF PHYSICAL FORCES. [BOOK 



of these aerial messengers could not be effected, the route followed 

 by them being at the will of the wind. The balloons had a chance 

 of three to one of coming to a friendly country, and, owing to this 

 fact, the greater number succeeded ; only a few fell into the Prussian 

 lines. One of them, la Ville d'Orleans, came down in Norway ; two 

 or three, indeed, were lost, probably in the sea. In the provinces, 

 several attempts were made to direct some aerostats towards Paris, 

 but they did not succeed. 



The only efficient means for the return of the correspondences was 

 the organization of the carrier-pigeon post ; further on we shall have 



FIG. 62.- -Departure of a balloon from tin works of la Villette. 



occasion to say a few words about it when we speak of microscopic 

 photography. 



As to the question of directing balloons, or to the more general 

 problems of aerial navigation, a question and problems much talked 

 about for the last twenty years, we have before stated that we shall 

 not refer to them here, for the simple reason that no real practical 

 solution has ever been proposed, or at least experimented on. How- 

 ever, we will mention a few interesting trials. 



Among the experimenters there are some who have abandoned, for 

 reasons which appear plausible, the idea of guiding at will machines 



