The prominent feature of Etrich’s monoplane was the elastic construction of its wings and tail. Across the rigid main bars of each wing were fastened numerous ribs with bamboo terminals, thus making the rear margin and tip of the wing flexible. Similarly the tail, or horizontal rudder, was framed of bamboo. Hence the pilot, by use of control wires, could flex both the wing margins and the tail up and down at will, to steer the machine, or he could let go the controls and allow the distorted surfaces to spring into their normal positions, and the machine to pursue the even tenor of its way. Moreover, the gusts and whirls in the air, on striking the elastic rear margins of the tail and wings, exert a propulsive effort. Thus could be utilized the wind’s energy of turbulence, as indicated by the present writer in 1893, in a paper on “Windgusts and Their Relation to Flight,” published in the _Proceedings of the International Conference on Aërial Navigation_ of that year. In passing it may be remarked that many other aëroplane designers, notably Bréguet, have emulated Mr. Etrich, though unconsciously perhaps, in providing elastic ribs, hinges or pivots to permit the rear parts of the wings and tails of their machines to yield freely to intentional or unusual impulses, and then spring back to their normal positions. [Illustration: FIG. 43.—THE ETRICH MONOPLANE OF 1910.] The carefully elaborated monoplane of Robert Esnault-Pélterie, which had been steadily improving for eight years, had now attained great perfection of finish, and merited prominence in actual flight. As shown in Plate XXIX, it had a general resemblance to the _Antoinette_, though differing throughout in its manifold details. The stream-line body was of steel tubing, braced with wire, and tightly covered with smooth fabric to reduce resistance. A five-cylinder R. E. P. motor in front connected directly with the two-blade propeller. The pilot sat between the wings with the passenger before him at the center of gravity, both having control levers when desired for instruction. The wings could be warped and the rudders, at the end of ample empennage planes, occupied the extreme rear as shown. An elastically cushioned skid between the two freely turning wheels served to absorb the shock of hard landing, though usually not touching the ground. The R. E. P. monoplane of 1910 was a very graceful, swift and strong machine, of marked efficiency.