THE INTERNAL WORK OF THE WINH. 23 



(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 sustained or even raised 

 indefinitely without expenditure of internal energy, other than that which is in- 

 volved in changing the aspect of its inclination at each pulsation. 



(4) That siuce (A) such a surface, having also power to change its inclina- 

 tion, 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 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) I add to the preceding results, which have been established here quali- 

 tatively, an expression of my personal opinion that they are realizable in practice. 



Finally, these observations and deductions have, it seems to me, an important 

 practical application not only as regards a living creature like the soaring bird, but 

 still more, as regards a mechanically constructed body, whose specific gravity may 

 probably be many hundred or even many thousand times that of the atmosphere. 

 We may suppose such a body to be supplied with fuel and engines, which would 

 be indispensable to sustain it in a calm, and yet which we now see might be ordi- 

 narily left entirely inactive, so that the body could supposably remain in the air, 

 and even maintain its motion in any direction, without expending its energy, 

 except as regards the act of changing the inclination or aspect which it presents to 

 the wind while the wind blew. 



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 will ever be able to 

 dispense altogether with the ability to rely at intervals on some internal source of 

 power, it will not be indispensable that this aerodrome of the future shall, in order 

 to go any distance — even to circumnavigate the globe without alighting, — need to 

 carry a weight of fuel which would enable it to perform this journey under con- 

 ditions analogous to those of a steamship, but that the fuel and weight need only 

 be such as to enable it to take care of itself in exceptional moments of calm. 



Washington, D. C: August, 1893. 



