It will be at once perceived from this figure that the portions of the screw marked _m_ and _n_ travel at a much lower speed than those portions marked _o_ and _p_, and these again more slowly than those marked _q_ and _r_ (compare with fig. 56, p. 120). 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 its several 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 the steel springs _z_, _s_. _a b_, _e f_, Tapering elastic reeds forming anterior or thick margins of blades of screw. _d c_, _h g_, Posterior or thin elastic margins of blades of screw. _m n_, _o p_, _q r_, Radii formed by the different portions of the blades of the screw when in operation. The arrows indicate the direction of travel.--_Original._] _A New Form of Aërial Screw._--If two of the wave wings represented at fig. 122, p. 239, be placed end to end, and united to a vertical portion of tube to form a two-bladed screw, similar to that employed in navigation, a most powerful elastic aërial screw is at once produced, as seen at fig. 130. This screw, which for the sake of uniformity I denominate _the aërial wave screw_, possesses advantages for aërial 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 is a self-adjusting, 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 efficacy to its shape and the graduated nature of its blades; the anterior margin of each blade being comparatively rigid, the posterior margin being comparatively flexible and more or less elastic. The blades are kites in the same sense that natural wings are kites. They are flown as such when the screw revolves. I find that the aërial wave screw flies best and elevates most when its blades are inclined at a certain upward angle as indicated in the figure (130). The aërial wave screw may have the number 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 them reciprocate; the one screw producing the current on which the other rises, as happens in natural wings.