1901.] on History and Progress of Aerial Locomotion. 489 



of the flying machine proper, the study of artificial flight by means 

 of wings, aeroplanes, or aerocurves and propellers, involves the investi- 

 gation of (1) the laws of aerial resistance of plane and curved surfaces 

 and screws ; (2) the lightest possible motors and sources of energy ; 

 (3) the conditions of balance and stability of a body in free air, sup- 

 ported by wings or aerocurves. The first of these three directions of 

 investigation having been dealt with by Lord Rayleigh, in his lecture 

 last year, we shall devote our chief attention to the second and third. 

 We may however notice, in passing, Langley's experiments on the 

 resistance of planes and curved surfaces, which confirmed Duchemin's 

 law, and showed that the greater the horizontal velocity of a surface 

 moving through the air the less is the horse-power necessary to sup- 

 port a given weight by it ; Phillips's Wealdstone experiments, on the 

 advantages of a number of narrow superposed planes (resembling a 

 Venetian blind), over a single wide plane of equal area, and Fitz- 

 gerald's investigation of the flapping flight of aeroplanes. 



With regard to the question of the motor, the experiments of Lili- 

 enthal, Pilcher and Chanute, agree in indicating that about two horse- 

 power would be required to convert their downward glides into hori- 

 zontal or slightly upward flights ; and Chanute estimates the possible 

 maximum weight of the motor required to drive a machine capable of 

 lifting one man off the ground, at 4 lbs. per horse-power with vertical 

 screws, 8 lbs. with flapping wings, and 14 lbs. with propeller-driven 

 aerocurves. Da Pra, from theoretical considerations, allows 15 kilo- 

 grammes per horse-power as the possible weight of the motor in his 

 design. Regarding the actual weight of motors, as long ago as 1868 

 Stringfellow gained a prize for a steam-engine and boiler weighing only 

 13 lbs., and giving rather over one horse-power. Maxim's gigantic 

 machine had an engine weighing 8 lbs. per horse-power. Langley is 

 reputed to have constructed a one horse-power engine weighing 7 lbs. ; 

 Hargreave one weighing 10 lbs. It should, however, be observed that 

 the heavier the machine the greater is the ratio of horse-power to 

 total weight necessary to render flight possible, and hence we see how 

 it is that birds are able to fly although they themselves weigh 150 to 

 200, and their muscles alone 5 to 20 lbs. per horse-power. For 

 models similar in form, but of different dimensions, the law commonly 

 assumed is that the horse-power per lb. of weight is proportional to 

 the square root of the linear dimensions, if the weight itself (as is 

 usually the case) is proportional to the cube of the linear dimensions. 



Thus, while the experimenters who attempted to fly, in the eight- 

 eenth and early part ot the nineteenth century, by their own muscular 

 power, were attempting an impossible task, owing to the fact that the 

 rate at which a man is capable of working (say about * horse-power) 

 is far below the amount required for flight, the difficulties arising from 

 the question of horse-power in proportion to weight can no longer be 

 regarded as insuperable. But, even if these purely mechanical diffi- 

 culties are overcome, we are far from having solved the problem of 



