About the same time another French inventor had actually built a balloon with a gas-bag shaped like an egg and placed horizontally with the blunt end foremost. The reduction in the resistance of the air to this form was so marked that the elongated gas-bag quickly displaced the former spherical shape. This balloon was held back from travelling at the full speed of the wind by the clever device of a rope dragging on the ground; and by a sail rigged so as to act on the wind which blew past the retarded balloon, the navigator was able to steer it within certain limits. It was the first dirigible balloon. In the same year the brothers Robert, of Paris, built an airship for the Duke of Chartres, under the direction of General Meusnier, a French officer of engineers. It was cylindrical, with hemispherical ends, 52 feet long and 32 feet in diameter, and contained 30,000 cubic feet of gas. The gas-bag was made double to prevent the escape of the hydrogen, which had proved very troublesome in previous balloons, and it was provided with a spherical air balloon inside of the gas-bag, which device was expected to preserve the form of the balloon unchanged by expanding or contracting, according to the rising or falling of the airship. When the ascension was made on July 6, 1784, the air-balloon stuck fast in the neck of the gas-bag, and so prevented the escape of gas as the hydrogen expanded in the increasing altitude. The gas-bag would have burst had not the Duke drawn his sword and slashed a vent for the imprisoned gas. The airship came safely to earth. It was General Meusnier who first suggested the interior ballonnet of air to preserve the tense outline of the form of the airship, and the elliptical form for the gas-bag was another of his inventions. In the building of the airship of the Duke de Chartres he made the further suggestion that the space between the two envelopes be filled with air, and so connected with the air-pumps that it could be inflated or deflated at will. For the motive power he designed three screw propellers of one blade each, to be turned unceasingly by a crew of eighty men. Meusnier was killed in battle in 1793, and aeronautics lost its most able developer at that era. [Illustration: The Scott airship, showing the forward “pocket” partially drawn in.] In 1789, Baron Scott, an officer in the French army, devised a fish-shaped airship with two outside balloon-shaped “pockets” which could be forcibly drawn into the body of the airship to increase its density, and thus cause its descent. It began to be realized that no adequate power existed by which balloons could be propelled against even light winds to such a degree that they were really controllable, and balloon ascensions came to be merely an adjunct of the exhibit of the travelling showman. For this reason the early part of the nineteenth century seems barren of aeronautical incident as compared with the latter part of the preceding century.