The germ of the invention of the balloon lies in the discovery of Mr Cavendish, made in 1766, thathydrogen gas, called inflammable air, is at least seven times lighter than atmospheric air. Foundingon this fact, Dr Black of Edinburgh proved by experiment that a very thin bag, filled with this gas, would rise to the ceiling of a room.In Dr Thomson's History of Chemistry, an anecdote, related by Mr Benjamin Bell, refers to this asfollows: -"Soon after the appearance of Mr Cavendish's paper on hydrogen gas, in which he made anapproximation to the specific gravity of that body, showing that it was at least ten times lighter thancommon air, Dr Black invited a party of friends to supper, informing them that he had a curiosity toshow them. Dr Hutton, Mr Clerk of Eldin, and Sir George Clerk of Penicuik, were of the number.When the company invited had arrived, he took them into a room where he had the allantois of acalf filled with hydrogen gas, and, upon setting it at liberty, it immediately ascended and adhered tothe ceiling. The phenomenon was easily accounted for; it was taken for granted that a small blackthread had been attached to the allantois, that the thread passed through the ceiling, and that someone in the apartment above, by pulling the thread, elevated it to the ceiling, and kept it in itsposition! This explanation was so plausible, that it was agreed to by the whole company, though, likemany other plausible theories, it turned out wholly fallacious, for, when the allantois was broughtdown, no thread whatever was found attached to it. Dr Black explained the cause of the ascent tohis admiring friends; but such was his carelessness of his own reputation, that he never gave the leastaccount of this curious experiment even to his class, and several years elapsed before this obviousproperty of hydrogen gas was applied to the elevation of balloons."Cavallo made the first practical attempts with hydrogen gas six years later, but he only succeeded incausing soap-bubbles to ascend.At last the art of aerial navigation was discovered in France, and in 1782 the first ascent was made.The triumph was achieved by Stephen and Joseph Montgolfier, sons of a wealthy paper-maker whodwelt at Annonay, on the banks of a rivulet which flows into the Rhone, not far from Lyon