310 ON AERIAL LOCOMOTION. 



power will be coiisuuumI in "slip," or iu giviDg a downward motiou to 

 the column oi" air. Even if a sufiflcieut force is obtained to keep a body 

 suspended by such means, yet, after the desired altitude is arrived at, 

 no further ascension is required ; there the apparatus is to remain sta- 

 tionary as to level, and its position, on the constantly yielding support 

 can only be maintained at an enormous expenditure of power, for the 

 screw can not obtain a hold upon afresh and unmoved portion of air in 

 the same manner as it does upon the body of water when propelling the 

 boat at full speed ; its action under these conditions is the same as when 

 the boat is held fast, in which case, although the engine is working up 

 to its usual rate, the tractive power is almost annulled. 



Some experiments made with a screw, or pair of inclined vanes acting 

 vertically in air, were tried in the following manner: To an upright 

 post was fixed a frame containing a bevel wheel and pinion, multiplying 

 in the ratio of three to one. The axle of the wheel was horizontal, and 

 turned by a handle of 5h inches radius. The spindle of the pinion 

 rotated vertically, and carried two driving-pins at the end of a cross- 

 piece, so that the top resembled the three prongs of a trident. The 

 upright shaft of the screw was bored hollow to receive the middle prong, 

 while the two outside ones took a bearing against a driving-bar, at right 

 angles to the lower end of the shaft, the top of which ended in a long 

 iron invot, running in a socket fixed in a beam overhead ; it could thus 

 rise and fall about 3 inches with very little friction. The top of the 

 screw-shaft carried a cross-arm, with a blade of equal size at each ex- 

 tremity, the distance from end to end being six feet. The blades could 

 be adjusted at any angle by clamping-screws. Both their edges and 

 the arms that carry them were beveled away to a sharp edge to dimin- 

 ish the effects of atmoshperic resistance. A wire stay was taken from 

 the base of each blade to the bottom of the upright shaft, to give rigid- 

 ity to the arms, and to prevent them from springing upwards. With 

 this apparatus experiments were made with weights attached to the up- 

 right screw-shaft, and the blades set at different pitches, or angles 

 of inclination. When the vanes were rotated rapidly, they rose and 

 fioated on the air, carrying the weights with them. Much difficulty 

 was experienced in raising a heavy weight by a comparatively small 

 extent of surface, moving at a high velocity ; the " slip " in these cases 

 being so great as to absorb all the power employed. The utmost effect 

 obtained in this way was to raise a weight of C pounds on 1 square foot 

 of sustaining surface, the planes having been set at a coarse pitch. To 

 keep up the rotation required about half the power a man could exert. 



The ratio of weight to sustaining surface was next arranged in the 

 proportion approximating to that of birds. Two of the experiments are 

 here quoted, which gave the most satisfactory results. Weight of wings 

 and shaft, 17i ounces; area of two wings, 121 inches — equal to 110 



