DR PETTIGREW ON THE PHYSIOLOGY OF WINGS. 419 



the impulse of the air which continues its effect, and naturally acts upon the 

 surface which it strikes, has the power of resolving itself into two forces, a 

 vertical and a horizontal force, the first suffices to raise the animal, the second to 

 move it along."* 



I have already adverted at considerable length (pages 413, 414, and 415) to 

 the movements and peculiarities of Professor Makey's artificial wing, and need 

 not again return to it. I will only observe, in passing, that it is not a little 

 curious that Borelli's artificial wing should have been reproduced at a distance 

 of nearly two centuries. 



The Author's Views: — his Method of Constructing and Applying Artificial 

 Wings as Contradistinguished from that of Borelli, Chabrier, Durckheim, 

 Marey, <%c. — The artificial wings which I have been in the habit of making for 

 several years differ from those recommended by Borelli, Durckheim, and 

 Marey in four essential points : — 



1st, The mode of construction. 



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



3d, The nature of the power employed. 



4th, The necessity of adopting certain elastic substances at the root of the 

 wing if in one piece, and at the root and in 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 composed of a rigid rod 



* Compare Marey's description with that of Borelli, a translation of which I subjoin. " Let 

 a bird be suspended in the air with its wings expanded, and first let the under surfaces (of the wings) 

 be struck by the air ascending perpendicularly to the horizon with such a force that the bird gliding 

 down is prevented from falling : I say that it (the bird) will be impelled with a horizontal forward 

 motion, because the two osseous rods of the wings are able, owing to the strength of the muscles, and 

 because of their hardness, to resist the force of the air, and therefore to retain the same form (literally 

 extent, expansion), but the total breadth of the fan of each wing yields to the impulse of the air when 

 the flexible feathers are permitted to rotate around the " manubria" or osseous axis, and hence it is 

 necessary that the extremities of the wings approximate each other : wherefore the wings acquire the 

 form of a wedge whose point is directed towards the tail of the bird, but whose surfaces are compressed 

 on either side by the ascending air in such a manner that it is driven out in the direction of its base. 

 Since, however, the wedge formed by the wings cannot move forward unless it carry the body of the 

 bird along with it, it is evident that it (the wedge) gives place to the air impelling it, and therefore 

 the bird flies forward in a horizontal direction. But now let the substratum of still air be struck 

 by the fans (feathers) of the wings with a motion perpendicular to the horizon. Since the fans aud 

 sails of the wings acquire the form of a wedge, the point of which is turned towards the 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 

 axis remaining rigidj 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 direc- 

 tion." — De Motu Animalium, pars prima, prop. 196, 1685. 



VOL. XXVI. PART II. 5 Q 



