FLYING AND FLYING-MACHINES. 341 



some degree. This gives the bird a clear advantage 

 over man, insomuch that man can never hope by his 

 unaided exertions to rival the bird in its own element. 

 It by no means follows, however, that because man may 

 never be able to rival the flight of the eagle or the 

 condor, of the pigeon or the swallow, he must therefore 

 needs be unable to fly at all. 



It should be remembered, also, that men can avail 

 themselves of contrivances by which a considerable 

 velocity may be acquired at starting ; and that when 

 the aeronaut is once launched with adequte velocity, a 

 comparatively moderate exertion of force may probably 

 enable him to maintain that velocity,- or even to increase 

 it. In this case, a moderate exertion of force would 

 also suffice to enable him to rise to a higher level. To 

 show that this is so, we need only return to the illus- 

 tration drawn from the kite. If a weight be attached 

 to a kite's tail, the kite, which will maintain a certain 

 height when the wind is blowing with a certain degree 

 of force, will rise to a greater height when the force of 

 the wind is but slightly increased. 



Kites afford, indeed, the most striking evidence of 

 the elevating power resulting from the swift motion of 

 an inclined plane through the air, the fact being 

 remembered always that, whatever supporting and 

 elevating power is obtained when air moves horizon- 

 tally with a certain velocity against an inclined plane, 

 precisely the same supporting and elevating power will 

 l>e obtained when the inclined plane is drawn or pro- 

 pelled horizontally with equal velocity through still air. 



