Page:Encyclopædia Britannica, Ninth Edition, v. 9.djvu/332

 320 FLIGHT briefly what is known regarding the history of the screw as applied to the air. The first suggestion on this subject was given by Paucton in 1768. This author, in his treatise on the Theorie de la Vis d Archimede, describes a machine provided with two screws which he calls a &quot; pte rophores.&quot; In 1796 Kir FIG. 3G. Caylcy s Flying Model (179fi). George Cayley gave a practical illustration of the efficacy of the screw as applied to the air by constructing a small machine, consisting of two screws made of quill feathers, a representation of which we annex (fig. 3G). Sir George writes as under : &quot;As it may be an amusement to some of your readers to see a machine rise in the air by mechanical means, I will conclude my present communication by describing an instrument of this kind, which any one can construct at the expense of ten minutes labour. &quot;a and b, fig. 36, arc two corks, into each of which are inserted four wing feathers from any bird, so as to be slightly inclined like the sails of a windmill, but in opposite directions in each set. A round shaft is fixed in the cork a, which ends in a sharp point. At the upper part of the cork b is fixed a whalebone bow, having a small pivot hole in its centre to receive the point of the shaft. The bow is then to be strung equally on each side to the upper portion of the shaft, and the little machine is completed. Wind up the string by turning the flyers different ways, so that the spring of the bow may unwind them with their anterior edges ascending ; then place the cork with the bow attached to it upon a table, and with a finger on the upper cork press strong enough to prevent the string from unwinding, and, taking it away suddenly, the instrument will rise to the ceiling.&quot; Cayley s screws were peculiar, inasmuch as they were superimposed and rotated in opposite directions. He esti mated that if the area of the screws was increased to 200 square feet, and moved by a man, they would elevate him. His interesting experiment is described at length, and the apparatus figured, in JVicolson s Journal, 1809, p. 172. Other experimenters followed Cayley at moderate inter vals : Deghen in 1816, Ottoris Sarti in 1823, and Dubo- chet in 1834. These inventors all constructed flying models on the vertical screw principle. In 1842 Mr Philips suc ceeded in elevating a steam model by the aid of revolving fans, which flew across two fields after having attained a great altitude ; and in 1859 Mr Bright took out a patent for a machine to be sustained by vertical screws, the model of which is to be seen at the patent museum, Ken sington, London. In 1863 the subject of aviation by vertical screws received a fresh impulse from the experi ments of MM. Ponton d Amecourt, De la Landelle, and Nadar, who exhibited models driven by clock-work springs, which ascended with graduated weights a distance of from 10 to 12 feet. These models were so fragile that they usually broke in coming in contact with the ground in their descent. Their flight, moreover, was unsatisfactory, from the fact that it only lasted a few seconds. Stimulated by the success of his spring models, M. Ponton d Ame court had a small steam model constructed. This model, which was shown at the exhibition of tho Aeronautical Society of Great Britain at the Crystal Palace in 1868, consisted of two superposed screws propelled by an engine, the steam for which was generated (for light ness) in an aluminium boiler. This steam model proved a failure, inasmuch as it only lifted a third of its own weight. Fi. 37 embodies M. de la Landelle s ideas. FIG. 37. n,n,o,p; g,r,s,t, screws arranged on vertical axes to act vertically upwards. The vertical axes are surmounted by two parachutes, and the body of the machine is furnished with an engine, propeller, rudders, and au exten sive aero-plane. (M. de la Landelle, 1863.) All the models referred to (Cayley s excepted 1 ) were pro vided with rif/id screws, which, for many reasons, we are disposed to regard as an error. In 1 87 2 M. Pe&quot;naud discarded the rigid screws in favour of elastic ones, as Professor Fettigrew had done some years before. M. Penaud also substituted india-rubber under torsion for the whalebone and clock springs of the smaller models, and the steam of the larger ones. His helicoptere or screw model is remarkable for its lightness, simplicity, and power. The accompanying sketch will serve to illustrate its con struction (fig. 38). It consists of two superposed elastic screws (a a, b I), the upper of which (a a) is fixed in a vertical frame (&amp;lt;?), which is pivoted in the central part (d) of the under screw. From the centre of the under screw an axle provided with a hook (e), which performs the part of a crank, projects in an upward direction. Between the hook or crank (e) and the centre of the upper 1 Cayley s screws, as explained, were made of feathers, and conse quently elastic. As, however, no allusion is made in his writings to the superior advantages possessed by elastic over rigid screws, it is to be presumed that feathers were employed simply for convenience and lightness. Professor Pettigrew, there is reason to believe, was the first to advocate the employment of elastic screws for aerial purposes.