Internal Work of the Wind. 447 



changes in an otherwise inert body, with what might almost 

 be called instinctive readiness and rapidity, does not really 

 demand intelligence or even instinct, but that the future 

 aerodrome may be furnished with a substitute for instinct, in 

 what may perhaps allowably be called a mechanical brain, 

 which yet need not, in his opinion, be intricate in its character. 

 His reasons for this statement, which is not made lightly, 

 must, however, be reserved for another time. 



It is hardly necessary to point out that the nearly inert 

 body in question may also be a human body, guided both by 

 instinct and intelligence, and that there may thus be a sense 

 in which human flight may be possible, although flight de- 

 pending wholly upon the action of human muscles be for ever 

 impossible. 



Let me resume the leading points of the present memoir 

 in the statement that it has been shown : — 



(1) That the wind is not even an approximately uniform 

 moving mass of air, but consists of a succession of very brief 

 pulsations of varying amplitude, and that, relatively to the 

 mean movement of the wind, these are of varying direction. 



(2) That it is pointed out that hence there is a potentiality 

 of " internal work " in the wind, and probably of a very great 

 amount. 



(3) That it involves no contradiction of known principles to 

 declare that an inclined plane, or suitably curved surface, 

 heavier than the air, freely immersed in, and moving with the 

 velocity of the mean wind, can, if the wind-pulsations here 

 described are of sufficient amplitude and frequency, be sus- 

 tained or even raised indefinitely without expenditure of 

 internal energy, other than that which is involved in changing 

 the aspect of its inclination at each pulsation. 



(4) That since (A) such a surface, having also power to 

 change its inclination, must gain energy through falling during 

 the slower, and expend energy by rising during the higher, 

 velocities ; and that (B) since it has been shown that there is 

 no contradiction of known mechanical laws in assuming that 

 the surface may be sustained or may continue to rise in- 

 definitely, the mechanical possibility of some advance against 

 the direction of the wind follows immediately from this 

 capacity of rising. It is further seen that it is at least 

 possible that this advance against the wind may not only be 

 attained relatively to the position of a body moving with the 

 speed of the mean wind, but absolutely, and with reference to 

 a fixed point in space. 



(5) The statement is made that this is not only mechanically 

 possible, but that, in the writer's opinion, it is realizable in 

 practice. 



