So many aerial voyages executed with safety encouraged other attempts ; and no accident occurred till the accomplished Pilatre de Rosier, with his companion liomain, were killed in an attempt to cross the channel from France to England. On the 18th of June, 1785, they ascended from Boulogne. Under the principal bal loon, which was of hydrogen gas, they had suspended, for the purpose of in creasing or the ascensional power at pleasure, a smoke balloon, which occasioned the disastrous issue. Scarcely a quarter of an hour had elapsed when the whole apparatus, at the height of 3000 feet, was perceived to be on fire, and the unfortunate voyagers were precipitated to the ground. This calamitous occur rence, however, did not damp the cour age of aeronauts. It was obvious that it had been occasioned by the want of pro per precautions ; accordingly ascents con tinued to be multiplied, and have since become so common as to be an ordinary spectacle in the principal cities of Europe.
When balloons first began to be con structed, it was expected that they would be found applicable to many important purposes. These expectations have been disappointed, chiefly because it has been found impossible to guide or control their course. The only power the aero naut possesses over his balloon is to regu late its elevation within certain limits. In one or two instances they have been successfully used for military reconnois sance. The victory which Jourdan ob tained over the Austrians at Fleurus, in 1794, was ascribed to the knowledge ob tained of the enemy's movements by means of a balloon. A very interesting ascent was made by Biot and Gay Lussac, in August 1804, and by Gay Lussac alone in September of the same year, with a view to make meteorological observations in the upper strata of the atmosphere. In the first voyage, the two philosophers, at an elevation of between 9,500 and 13,000 English feet, found the oscillations of the magnetic needle to be performed in the same time as at the surface of the earth. At 12,800 feet the thermometer, which stood at 63P at the observatory, had sunk to 51° of Fahrenheit, being only a decrease of 1° for every thousand feet. The hygroscope indicated increased
dryness in proportion to the elevation. In the second ascent, performed by Gay Lussac alone, the venation of the com pass at the height of 12,680 was found to remain unaltered. At 14,480 feet, a key held in the magnetic direction attracted with one end and repelled with the other the north pole of the magnetic needle. The same was the case at 20,150. At 18,000 feet the thermometer fell to the freezing point, and at 22,912 feet to 14-9° of Fehr. Two flasks, which had been previously emptied of air, were opened and filled at an elevation exceeding 21,400 feet ; and the air brought down from this region was found, on being analyzed, to contain exactly the same proportions of the constituent elements as at the surface. The utmost elevation which be reached was 23,040 feet, or four miles and a quar ter above the level of the sea, consider ably higher than the loftiest peak of the Andes.
Excepting in these two remarkable as cents of Gay Lussac, nothing has been gained to science by the use of balloons. The numerous other ascents undertaken, both before and since, have as yet served no other purpose than to gratify idle curi osity; and from the total failure of every scheme that has been proposed for direct ing their course through the air, there is little r•son to anticipate any great advan tages from them to society. Neverthe less, the comparative cheapness and fa cility with which they can be filled by coal gas, now so generally used for the purposes of illumination, have been the cause of directing public attention to the subject. Mr. Green crossed the channel from Vauxhall to in Germany, in 1836, after a journey of eighteen hours, carrying two companions and a ton of ballast. This feat (crossing the English Channel), has been repeated since more than once,—the last voyage being in the spring of 1851 from London, and landing within a few miles of Boulogne.