As has been already stated, M. Dupuy de Lome, at the end of the siege of Paris, was engaged in building a navigable balloon, which, owing to the unsettled state of affairs in France, did not receive its trial till two years later. This balloon, which was inflated with pure hydrogen, was of greater capacity than that of M. Giffard, being cigar shaped and measuring 118 feet by 48 feet. It was also provided with an ingenious arrangement consisting of an internal air bag, capable of being either inflated or discharged, for the purpose of keeping the principal envelope always distended, and thus offering the least possible resistance to the wind. The propelling power was the manual labour of eight men working the screw, and the steerage was provided for by a triangular rudder. The trial, which was carried out without mishap, took place in February, 1872, in the Fort of Vincennes, under the personal direction of the inventor, when it was found that the vessel readily obeyed the helm, and was capable of a speed exceeding six miles an hour.