This construction offered a two-fold advantage in its resistance to both torsion and bagging, for as the pressures upon the wing were nearly balanced about the middle rib, the tendency to twist was reduced to a minimum, while the bagging, which results from the bending of the framework, as distinct from [p087] its twisting, was greatly reduced by the manner in which the frame was put together, the whole construction permitting a return to the system of wire guying at first adopted, which had been found inapplicable to a wing having but a single longitudinal rib forming its front margin. When completed, the wings were strongly guyed with piano wire, both above and below, to guy-posts attached to the midrod, and each cross-rib was separately guyed with wire chords. Although these wings had cost much in time and labor, and contained many points of improvement, they were eventually found to be too weak to support the aerodrome, and were therefore abandoned without a trial in the field. For the plane horizontal tail hitherto used a pair of curved wings was substituted, similar in all respects to those just described, but having only half their area, and these were later replaced by a pair equal in size and in every way the counterpart of the front wings. The tail as hitherto used accordingly disappeared, and gave place to another having a wholly different function to perform; for while the old tail, like the rear pair of wings which superseded it, was intended to bear a definite part of the weight of the aerodrome, the new tail which was now added behind the rear pair of wings was not supposed to bear any part whatever of the weight, but to act solely as a guide, and this new feature, first introduced in October, 1895, was continued to the end. This arrangement of the surfaces is quite different from that adopted by Pénaud in 1872, in which the tail became automatic in its action through its small angle of elevation as compared with that of the wings, while still acting as a supporting surface, whereas in the present arrangement the function of the tail was solely one of guidance. This, I believe, was one of the important changes which perhaps as much as any other led to final success. During the fall of 1895 a large number of experiments were made both in free flight with gliding models, and in constrained flight with the whirling-table, to determine the relative lifting power of the front and rear wings per unit of area, and from these the following new rules were deduced for finding the center of pressure: If a following wing is the size of the leader, assume that its efficiency is 66 per cent per unit of surface. If it is half the size of the leader, assume that its efficiency is 50 per cent per unit of surface. If it is half as large again as the leader, assume that its efficiency is 80 per cent per unit of surface. For intermediate sizes of surface, proportionate values per unit of surface may be assumed.