Wenham[103] has advocated the employment of _superimposed planes_, with a view to augmenting the support furnished while it diminishes the horizontal space occupied by the planes. These planes Wenham designates _Aëroplanes_. They are inclined at a very slight angle to the horizon, and are wedged forward either by the weight to be elevated or by the employment of vertical screws. Wenham’s plan was adopted by Stringfellow in a model which he exhibited at the Aëronautical Society’s Exhibition, held at the Crystal Palace in the summer of 1868. [103] “Aërial Locomotion,” by F. H. Wenham.--_World of Science_, June 1867. The subjoined woodcut (fig. 110), taken from a photograph of Mr. Stringfellow’s model, gives a very good idea of the arrangement; _a b c_ representing the superimposed planes, _d_ the tail, and _e f_ the vertical screw propellers. [Illustration: FIG. 110.--Mr. Stringfellow’s Flying Machine.] The superimposed planes (_a b c_) in this machine contained a sustaining area of twenty-eight square feet in addition to the tail (_d_). Its engine represented a third of a horse power, and the weight of the whole (engine, boiler, water, fuel, superimposed planes, and propellers) was under 12 lbs. Its sustaining area, if that of the tail (_d_) be included, was something like thirty-six square feet, _i.e._ three square feet for every pound--the sustaining area of the gannet, it will be remembered (p. 134), being less than one square foot of wing for every two pounds of body. The model was forced by its propellers along a wire at a great speed, but, so far as I could determine from observation, failed to lift itself notwithstanding its extreme lightness and the comparatively very great power employed.[104] [104] Mr. Stringfellow stated that his machine occasionally left the wire, and was sustained by its superimposed planes alone.