During the time of which we are speaking there was living in London a famous chemist named Henry Cavendish. He was the son of a nobleman, and a very rich man; but he shut himself up entirely from the world, and devoted his whole time and energies to the study of science. So afraid was he of being interrupted in his work that he lived the life of a hermit, commanding his servants to keep out of his sight on pain of dismissal, and ordering his dinner daily by means of a note placed on the hall table. In the year 1760--twenty-two years before the Montgolfier brothers began their experiments--this eccentric man had discovered what was then known as “inflammable air,” but what we now call hydrogen gas. Cavendish’s experiments proved that hydrogen is the lightest of all known substances, being about fourteen times lighter than atmospheric air; and soon after he had made known his researches, it occurred to a certain Dr. Black of Edinburgh that if a sufficiently thin and light bladder were filled with this “inflammable air” it would rise upwards. Dr. Black even went so far as to order a special bladder to be prepared for the purpose; but by the time it was ready he was busy with other work, and the experiment was never made; otherwise it is extremely probable that the honour of inventing the balloon would have been won for this country, and not for France. A little later Tiberius Cavallo, an Italian chemist living in England, came yet nearer to the great invention, for he filled a number of soap-bubbles with the newly discovered gas, and saw them float high into the air. He did not, however, think at the time that his experiments would lead to any practical result, and so the matter dropped entirely, until the world was suddenly electrified by the tidings of the wonderful hot-air balloon invented by the brothers Montgolfier at Annonay. The news of this discovery recalled to the minds of many the almost forgotten experiments of the past, and it was forthwith suggested that balloons might be inflated with hydrogen gas more successfully than with hot air. It was resolved immediately to put this theory to the test. A large subscription to defray expenses was raised in Paris without difficulty, for men’s minds were keen on the new-found art of sailing the sky; and M. Charles, Professor of Experimental Philosophy, and two brothers, the Messrs. Roberts, well-known mechanicians, were appointed to construct a suitable balloon and inflate it by the new method.