AERONAUTICS. 



227 



account, not only always looks forwards, but it forms a true 

 kite with the horizon, the angles made by the kite varying at 

 every part of the down stroke, as shown more particularly at 

 e, f, g ; j, k, I, m of fig. 88, p. 166. I am therefore opposed 

 to Borelli, Macgillivray, Owen, Bishop, M. Liais, the Duke of 

 Argyll, and Mareyas to the direction and nature, of the down 

 stroke. I differ also as to the direction and nature of the up 

 stroke. 



Professor Marey states that not only does the posterior 

 margin of the wing yield in an upward direction during 

 the down stroke until the under surface of the pinion makes 

 a backward angle of 45° with the horizon, but that during 

 the up stroke it yields to the same extent in an opposite direc- 

 tion. The posterior flexible margin of the wing, according 

 to Marey, passes through a space of 90° every time the wing 

 reverses its course, this space being dedicated to the mere 

 adjusting of the planes of the wing for the purposes of 

 flight. The planes, moreover, he asserts, are adjusted not by 

 vital and vito-mechanical acts but by the action of the air 

 alone ; this operating on the under surface of the wing and 

 forcing its posterior margin upwards during the down stroke ; 

 the air during the up) stroke acting upon the posterior margin 

 of the upper surface of the wing, and forcing it downwards. 

 This is a mere repetition of Borelli's view. Marey dele- 

 gates to the air the difficult and delicate task of arranging 

 the details of flight. The time, power, and space occupied 

 in reversing the wing alone, according to this theory, are such 

 as to render flight impossible. That the wing does not act 

 as stated by Borelli, Marey, and others may be readily proved 

 by experiment. It may also be demonstrated mathematically, 

 as a reference to figs. 114 and 115, p. 228, will show. 



Let a & of fig. 1 1 4 represent the horizon ; m n the line of 

 vibration ; x c the wing inclined at an upward backward 

 angle of 45° in the act of making the down stroke, and xd 

 the wing inclined at a downward backward angle of 45° and 

 in the act of making the up stroke. When the wing xc 

 descends it will tend to dive downwards in the direction / 

 giving very little of any horizontal support (a b) ; when the 

 wing X d ascends it will endeavour to rise in the direction g, as 

 it darts up like a kite (the body bearing it being in motion). 



