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Rh weight of the water they should hold, or the crushing force of the atmosphere after exhaustion. Unlike the product of Bacon's imagination, his conception was a correct application of demonstrated physical laws; but, had it been tested by experiment, he would at once have found that there were other laws which he had not taken into account. In his view, the only obstacle to success was that "the Almighty would never allow an invention to succeed by means of which civil government could so easily be disturbed." Air-ships floating beyond the reach of missiles, if only capable of being accurately directed, might well have been thought more terrible than dynamite is to-day.

Soon after the discovery of hydrogen gas by Cavendish and Watt in 1766, experiments were made with a view to utilizing it for the purpose of lifting bodies into the air. But, until 1783, nothing more substantial than a soap-bubble could be made thus to ascend. Joseph Montgolfier, who was a successful manufacturer of paper, tried bags of this material; but hydrogen was found to diffuse so rapidly through it that the idea was abandoned by him. Observing that clouds of vapor and smoke remained floating at various heights, he thought that, if they could be confined in bags of paper, these might be made to float in like manner. Since the experiments of Franklin in 1752 had proved the existence of atmospheric electricity, the idea gained currency that the lightness of clouds and of smoke was in some way due to electric charge. A paper bag was made, and, with its opening downward, a fire was kindled, "as well to increase the layer of electric fluid upon the vapor in the vessel as to divide the vapors into smaller molecules and dilate the gas in which they are suspended." The bag was carried up to a considerable height. Montgolfier seems not to have attributed the ascension to the effect of heat in diminishing the specific gravity of the contained air. The first successful experiment in ballooning was thus based on a misconception.

Montgolfier's first public exhibition of his invention was made on June 5, 1783. The news of his success was rapidly spread; and at Paris a balloon was soon constructed under the superintendence of M. Charles, who substituted hydrogen for smoke, confining it in a bag of varnished silk instead of paper and linen. The ascension was successfully accomplished on the 27th of August. Charles at once proceeded to the construction of a new and much larger balloon, in which he ascended with his colleague, Robert, on the 1st of December, making a journey of more than twenty-five miles. This balloon was provided with a safety-valve of Charles's invention, a hoop, to which the car was attached, and netting intended to equalize the distribution of weight upon the balloon. It was in all important particulars the same as the balloon almost universally employed throughout a century afterward. Montgolfier made several exhibitions of his hot-air balloons at Paris, and in one of these, on the 15th of October, M. Pilâtre de