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THE POPULAR SCIENCE MONTHLY. 



kinson shows that he had quite definite views about the application of 

 the principle of the screw-propeller to the direction of aerostatic ma- 

 chines, 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 aeronaut 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 high- 

 est distinction, M. Giffard, constructed an elongated balloon (Fig. 1), 



Fio. 1. Giffard's Aerial Steamer, 1852. 



pointed at both ends and filled with illuminating gas. Suspended be- 

 neath 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 head- 



