When Franklin last saw the vanishing form of this balloon, it appeared no bigger than a walnut. The experiment proved a most prosperous one. From first to last the aerial navigators retained perfect command of their air-ship, descending, when they pleased, by letting some of the air in it escape, and rising, when they pleased, by discharging sand; and at one time skimming over a field so low as to be able to talk to some laborers. Pleased as Franklin was with the experiment, he wrote to Henry Laurens that he yet feared that the machine would hardly become a common carriage in his time, though, being the easiest of all _voitures_, it would be extremely convenient to him, now that his malady forbade him the use of the old ones over a pavement. The idea, however, was such an agreeable one to him that, when he returned to Philadelphia, he wrote to his friend Jean Baptiste Le Roy that he sometimes wished that he had brought a balloon from France with him sufficiently large to raise him from the ground, and to permit him, without discomfort from his stone, to be led around in his novel conveyance by a string, attached to it, and held by an attendant on foot. On the whole, it appeared to Franklin that the invention of the balloon was a thing of great importance. Convincing sovereigns of the Folly of Wars [he wrote to Ingenhousz] may perhaps be one Effect of it; since it will be impracticable for the most potent of them to guard his Dominions. Five thousand Balloons, capable of raising two Men each could not cost more than Five Ships of the Line; and where is the Prince who can afford so to cover his Country with Troops for its Defence, as that Ten Thousand Men descending from the Clouds might not in many places do an infinite deal of mischief, before a Force could be brought together to repel them?