Page:Popular Science Monthly Volume 27.djvu/316

300 shows that he had quite definite views about the application of the principle of the screw-propeller to the direction of aërostatic machines, though in his day screw-propellers had not yet been applied even to surface navigation.

Hopkinson's suggestion did not then find its way into print. Even had it been published, the means were wanting for any experiments on a large scale. It would have been a noteworthy step in the right direction, but the muscular power of his imaginary aëronaut would have been far from sufficient to control the propeller. Nearly seventy years elapsed before his idea, independently evolved by another, was put to the test; and during this interval ballooning was but rarely applied to any other purpose than that of public display. The fruitless attempts to direct balloons were often made the subject of caricature.

In 1852 a young French engineer, who subsequently won the highest distinction, M. Giffard, constructed an elongated balloon (Fig. 1),



pointed at both ends and filled with illuminating gas. Suspended beneath it by cords was a longitudinal shaft, at the end of which was a triangular sail that could be turned about an almost vertical axis and be made to serve the purpose of a rudder. About twenty feet beneath the shaft was hung a framework of wood, on which rested a small steam-engine, whose piston gave motion to a screw-propeller. The weight of the machine, including furnace, boiler, coal, and water, was not quite fourteen hundred pounds. On the 24th of September Giffard ascended with it over Paris to the height of five thousand feet. The wind was quite strong; but he was able to make very perceptible