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322 Professor Pettigrew (fig. 18, page 313), or with Professor Pettigrew s artificial wing (page 319, fig. 32), tho identity of principle and application is at once apparent. The twisting kite-like action of the wings, to which allusion has so frequently been made, and to which, as has been shown, Professor Pettigrew first strongly directed attention in 1867, justifies our introductory remarks as to the very intimate relation which subsists between natural and artificial flight. As already stated, it is not possible to understand artificial flight in the absence of a knowledge of natural flight. In M. P^.naud s artificial bird the equilibrium is secured by the addition of a tail. The model cannot raise itself from the ground, but on being liberated from the hand it descends 2 feet or so, when, having acquired initial velocity, it flies horizontally for a distance of 50 or more feet, and rises as it flies from 7 to 9 feet. The following are the measurements of the model in question : length of wing from tip to tip, 32 inches ; weight of wing, tail, frame, india-rubber, &c., 73 grammes (about 2| ounces). We have referred to Mr Henson s flying machine, which was designed in 1843, As it was the earliest attempt at aerostation on a great scale it deserves a more than passing notice. Mr Henson was one of the first to combine aerial screws with extensive supporting structures occupying a nearly horizontal position. The accompanying illustration explains the combination (fig, 41), FIG. 41. Henson s Aerostat (1843). "The chief feature of the invention was the very great expanse of its sustaining planes, which were larger in proportion to the weight it had to carry than those of many birds. The machine advanced with its front edge a little raised, the effect of which was to present its under surface to the air over which it passed, the re sistance of which, acting upon it like a strong wind on the sails of a windmill, prevented the descent of the machine and its burden. The sustaining of the whole, therefore, depended upon the speed at which it travelled through the air, and the angle at which its under surface impinged on the air in its front The machine, fully prepared for flight, was started from the top of an inclined plane, in descending which it attained a velocity necessary to sustain it in its further progress. That velocity would be gradually destroyed by the resistance of the air to the forward flight ; it was, therefore, the office of the steam-engine and the vanes it actuated simply to repair the loss of velocity ; it was made, therefore, only of the power ami Aveight necessary for that small effect." The editor of Newton s Journal of Arts and Sciences speaks of it thus : " The apparatus consists of a car containing the goods, passengers, engines, fuel, &c. , to which a rectangular frame, made of wood or bamboo cane, and covered with canvas or oiled silk, is attached. This frame extends on either side of the car in a similar manner to the outstretched wings of a bird ; but with this difference, that tlie frame is immovable. Behind the wings are two vertical fan wheels, furnished with oblique vanes, which arc intended to propel tho apparatus through the air. The rainbow-like circular wheels are the propellers, answering to the wheels of a steam-boat, and acting upon the air after the manner of a windmill. These wheels receive motions from bands and pulleys from a steam or other engine, contained in the car. To an axis at the stern- of the car a triangular frame is attached, resembling the tail of a bird, which is also covered with canvas or oiled silk. This may be expanded or contracted at pleasure, and is moved up and down for the purpose of causing the machine to ascend or descend. Beneath the tail is a rudder for directing the course of the machine to the right or to the left ; and to facilitate the steering a sail is stretched between two masts which rise from the car. The amount of canvas or oiled silk necessary for buoying up tho machine is stated to be equal to one square foot for each half pound of weight." The defect of Mr Henson s machine consists mainly in its rigidity, and in the vast amount of sustaining suri ace displayed by it, this approximating it in some measure to the balloon. Mr Wenham, thinking to improve upon Mr Henson, invented in 1867 what he designated his aero-planes. 1 The aero-planes are thin, light, long, narrow structures, arranged above each other in tiers like so many shelves. They are tied together at a slight upward angle, and combine strength and lightness. The idea is to obtain great sustain ing area in comparatively small space. It was hoped that when the aero-planes were wedged forward in the air by vertical screws, or by the body to be flown, each aero-plane would rest or float upon a stratum of undisturbed air, and that practically the aero-planes would give the same support as if spread out horizontally. The aero-planes may be said to form a compound kite, and have only been partially successful. They are rigid, and present a large extent of dead surface, so that the same objections made to Mr Hen- son s arrangement apply to them. The great sustaining surface they present forms at once their strength and weak ness. They sustain and lift, but are very difficult to wedge forward, and if a breeze be blowing they become unmanageable, in the sense that a balloon is unmanageable. The accompanying figures illustrate Mr Wenham s views (figs. 42 and 43). Fig. 42. Fig. 43. FIG. 42 represents a system of aero-planes designed to carry a man. a, a, thin planks, tapering at each end, and attached to a triangle ; I, similar plank for supporting the aeronaut; c, c, thin bands of iron which truss planks a, a_; rf, rf, vortical rods. Between these are stretched five bands of holland 15 inches broad and 1C feet long, the total length of, the wel) being 80 feet. This apparatus, when caught by a gust of wind, actually lifted the aeronaut. (Wenham, 1867.) FIG. 43. A system of aero-planes similar to that represented at fig. 42. a a, main spar 1C feet long; b, b, panels, with base board for aeronaut attached to main spar; e e, thin tie-band of steel with struts starting from mam spar. This forms a strong light framework for the aero-planes, consisting of s: webs of thin holland 15 inches broad. The aero-planes are kept in parallel plane by vertical divisions of holland 2 feet wide, c, c, wing propellers driven by the feet. (Wenham, 1867.) Mr Stringfellow, who was originally associated with Mr Henson, and constructed a successful flying model in 1847, built a second model in 1868, in which Mr Wenham s aero-planes were combined with aerial screws. This model was on view at the Exhibition of the Aeronautical Society of Great Britain, held at the Crystal Palace, London, in 1868. It was remarkably compact, elegant, and light, and obtained the XI 00 prize of the exhibition for its engine, which was the lightest and most powerful ever constructed. The annexed woodcut (fig. 44), 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, e, f the vertical screw propellers. The super imposed planes (a, b, c) in this machine contained a sus taining area of 28 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, superim posed planes, and propellers) was under 12 B). Its sus taining area, if that of the tail (d) be included, was some thing like 36 square feet, i.e., 3 square feet for every 1 "On Aerial Locomotion," Aeronautical Society s Report for 1867.