NO. 8' SAMUEL PIERPONT LANGLEY ABBOT 



45 



motionless wings, for without this evidence of the iX)ssibiHty of action 

 which now ceases to approach the inconceivable, we are not likely, 

 even if admitted its theoretical possibility, to have thought the mecha- 

 nism solution of this problem possible. But although to show how 

 this physical miracle of nature is to be imitated, completely and in 

 detail, may be found to transcend any power of analysis, I hope to 

 show, that this may l>e possible without invoking the asserted power 

 of 'Aspiration' relative to curved surfaces, or the trend of upward cur- 

 rents, and even to indicate the probability that the mechanical solu- 

 tion of this problem may not be beyond human skill. 



" Let me resume the leading points of the present memoir in the 

 statement that it has been shown : 



"(i) 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 de- 

 clare 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 ampli- 

 tude and frequency, be sustained 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 iimy be sustained or 

 may continue to rise indefinitely, 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. 



" The final application of these principles to the art of aerodromics 

 seems then to be that, while it is not likely that the perfected aerodrome 



