In the condition of ignorance of the properties of gases that existed in that age, it did not occur, and could not have occurred, to Père Galien to use other gases than air; no more could he have thought of employing heat to rarefy the air, for the first not very precise notions on the decrease in densities of gases by heat only date from Priestley. But when Cavendish, in 1765, had fully studied hydrogen gas, and shown that as it was prepared then it was seven times lighter than air, Black was enabled to suggest that by filling a light bag with hydrogen the bag would be able to raise a certain weight in the air. The labors of Cavendish, Black, and the discoveries of oxygen, nitrogen, and other gases by Priestley, were described by Priestley a few years afterward in the celebrated book on The Different Kinds of Air--a book which Stephen and Joseph Montgolfier had in their possession. The two brothers evidently found the germ of their invention in it. It is fair to say that the Montgolfiers, who were already known in the learned world by their discoveries in the mechanical sciences, had thought, before they knew of Priestley's book, of a way of imitating Nature by inclosing vapor of water, a gas lighter than air, in a paper bag, which would be lifted up, the vapor contained in the bag being sustained in the air like a cloud. But the vapor condensed, and the weighted balloon shortly fell to the ground. The smoke produced by burning wood inclosed in a bag gave no better results. After seeing Priestley's book, they substituted hydrogen for vapor and for smoke, but the gas passed through the paper bag, and they gave up this attempt. They then fancied that electricity was one of the causes of the rise of clouds, and sought for a gas that had electrical properties. They thought they could obtain it by burning wet straw and wool together. A box made of silk was filled with this gas, and they had the great satisfaction of seeing it rise to the ceiling of their room, and, in a second experiment, into the air. This was in November, 1782. Five months previously, Tiberius Cavallo, in England, had repeated Black's experiment of filling a paper sack with hydrogen; but, as the Montgolfiers had found, the hydrogen leaked through the paper. Cavallo had better success with soap bubbles, which held the gas. His experiments stopped here, while the Montgolfiers carried theirs on to practical success.--_Translated for the Popular Science Monthly from the Revue Scientifique._ SKETCH OF EDWARD ORTON, LATE STATE GEOLOGIST OF OHIO; LATE PRESIDENT OF THE AMERICAN ASSOCIATION FOR THE ADVANCEMENT OF SCIENCE.