AERONAUTICS. 



235 



out, and need not be again referred to. It is not a little 

 curious that Borelli's artificial wing should have been 

 reproduced in its integrity at a distance of nearly two 

 centuries. 



The Author's Views: — his Method of constructing and applying 

 Artificial JVings as contra-distinguished from that of Borelli, 

 Chabrier, Durckheim, Marey^ etc. — The artificial wings which I 

 have been in the habit of making for several years diff*er from 

 those recommended by Borelli, Durckheim, and Marey in 

 four essential points : — 



1^^, The mode of construction. 



2d, The manner in which they are applied to the air. 



Zd, The nature of the power employed. 



Uh, The necessity for adapting certain elastic substances 

 to the root of the wing if in one piece, and to the root and 

 the body of the wing if in several pieces. 



And, first, as to the manner of construction. 



Borelli, Durckheim, and Marey maintain that the anterior 

 margin of the wing should be rigid ; I, on the other hand, 

 believe that no part of the wing whatever should be rigid, 

 not even the anterior margin, and that the pinion should be 

 flexible and elastic throughout. 



That the anterior margin of the wing should not be com- 

 posed of a rigid rod may, I think, be demonstrated in a 

 variety of ways. If a rigid rod be made to vibrate by the 

 hand the vibration is not smooth and continuous ; on the 

 contrary, it is irregular and jerky, and characterized by two 

 halts or pauses (dead points), the one occurring at the end of 

 the up stroke, the other at the end of the down stroke. This 

 mechanical impediment is followed by serious consequences 

 as far as power and speed are concerned — the slowing of the 

 wing at the end of the down and up strokes involving a 



acquire the form of a wedge, the point of which is turned towards tlie tail 

 (of the bird), and since they suffer the same force and compression from 

 the air, whether the vibrating wings strike the undisturbed air beneath, or 

 whether, on the other hand, the expanded wings (the osseous axes remain- 

 ing rigid) receive the percussion of the ascending air ; in either case the 

 flexible feathers yield to the impulse, and hence approximate each other, and 

 thus the bird moves in a forward direction.'^'' — De Motu Animalium, pars 

 prima, prop. 196, 1685. 



