224 



AfiRONAUTICS. 



air perpendicularly from above, the posterior and flexible 

 portion of the wing will yield and be forced in an upward 

 direction. 



Fifth, That this u^pward yielding of the posterior or flexible 

 margin of the wing results in and necessitates a horizontal 

 transference of the body of the bird. 



Sixth, That to sustain a bird in the air the wings must 

 strike vertically downwards, as this is the direction in which a 

 heavy body, if left to itself, would fall. 



Seventh, That to propel the bird in a horizontal direction, 

 the wings must descend in a perpendicular direction, and the 

 posterior or flexible portions of the wings yield in an upward 

 direction, and in such a manner as virtually to communicate 

 an oblique action to them. 



Eighth, That the feathers of the wing are hent in an 

 upward dArection when the wing descends, the upward bending 

 of the elastic feathers contributing to the horizontal travel of 

 the body of the bird. 



I have been careful to expound Borelli's views for several 

 reasons : — 



\sty Because the purely mechanical theory of the wing's 

 action is clearly to be traced to him. 



2d, Because his doctrines have remained unquestioned for 

 nearly two centuries, and have been adopted by all the writers 

 since his time, without, I regret to say in the majority of 

 cases, any acknowledgment whatever. 



?>d, Because his views have been revived by the modern 

 French school ; and 



Uh, Because, in commenting upon and diflering from 

 Borelli, I will necessarily comment upon and differ from all 

 his successors. 



As to the Direction of the Stroke, yielding of the Wing, etc, — 

 The Duke of Argyll^ agrees with Borelli in believing that the 

 wing invariably strikes perpendicularly downwards. His words 

 are — " Except for the purpose of arresting their flight birds 

 can never strike except directly downwards ; that is, against 

 the opposing force of gravity." Professor Owen in his Com- 

 parative Anatomy, Mr. Macgillivray in his British Birds, Mr. 

 Bishop in his article " Motion " in the Cyclopedia of Anatomy 

 1 " Reign of Law "-Good Words, 1865. 



