1872.] Natural and Artificial Flight. 207 
This screw, which for the sake of uniformity I denominate 
the aérial wave screw, possesses advantages for aérial purposes 
to which no form of rigid screw yet devised can lay claim. 
The way in which it clings to the air during its revolution 
and the degree of buoying power it possesses are quite 
astonishing. It isa self-ajusting, self-regulating screw, and as 
its component parts are flexible and elastic, it accommodates 
itself to the speed at which it is driven, and gives a uniform 
buoyancy. The slip I may add is nominal in amount. This 
screw is exceedingly light, and owes its efficiency to its shape 
and the graduated nature of its blades, the anterior margin 
of each blade being comparatively rigid, the posterior margin 
Fiac. 16. 
Fig. 16. Aérial wave screw whose blades are slightly twisted upon themselves 
(a b,c d; ef, gh), so that those portions nearest the root (d h) make a 
greater angle with the horizon than those parts nearer the tip (bf). The 
angle is thus adjusted to the speed attained by the different portions of the 
screw. The angle admits of further adjustment by means of the steel 
springs, z, s, these exercising a restraining, and to a certain extent a 
regulating, influence which effectually prevents shock. 
It will be at once perceived from this figure that the portions of the screw 
marked m and ” travel at a much lower speed than those portions marked 
o and p, and these again more slowly than those marked qand yr. As, 
however, the angle which a wing or a portion of a wing, as I have pointed 
out, varies to accommodate itself to the speed attained by the wing, or a 
portion thereof, it follows, that to make the wave screw mechanically 
perfect, the angles made by itsseveral portions must be accurately adapted 
to the travel of its several parts as indicated above. 
x, Vertical tube for receiving driving shaft. v, w, Sockets in which the roots 
of the blades of the screw rotate, the degree of rotation being limited by 
steel springs, z, s. ab, e f, Tapering elastic reeds forming anterior or 
thick margins of blades of screw. dc, h g, Posterior or thin elastic 
margin of blades of screw. mun,op,qy7, Radii formed by the different 
portions of the blades of the screw when in operation. The arrows 
indicate the dire¢tion of travel. 
being comparatively flexible and more or less elastic. 
The blades are kites in the same sense that natural wings 
are kites, and are flown as such when the screw revolves. 
I find the aérial wave screw flies best and elevates most 
when its blades are inclined at a certain upward angle, as 
indicated in Fig. 16. The aérial wave screw may have 
the numbers of its blades increased by placing the one 
above the other, and two or more screws may be combined 
and made to revolve in opposite directions so as to make 
