226 



AERONAUTICS. 



to" the whole line of both wings a corresponding push forwards 

 to the body of the bird. The same volume of air is thus 

 made, in accordance with the law of action and reaction, to 

 sustain the bird and carry it forward,'''^ Mr. Macgillivray 

 observes that " to progress in a horizontal direction it is neces- 

 sary that the downward stroke should be modified by the ele- 

 vation in a certain degree of the free extremities of the quills^ 



Marey's Views. — Professor Marey states that during the 

 down stroke the posterior or flexible margin of the wing yields 

 in an upward direction to such an extent as to cause the under 

 surface of the wing to look backwards, and make a backward 

 angle with the horizon of 45*" plus or minus according to 

 circumstances.^ That the posterior margin of the wing yields 

 in a slightly upward direction during the down stroke, I 

 admit. By doing so it prevents shock, confers continuity of 

 motion, and contributes in some measure to the elevation of 

 the wing. The amount of yielding, however, is in all cases 

 very slight, and the little upward movement there is, is in 

 part the result of the posterior margin of the wing rotating 

 around the anterior margin as an axis. That the posterior 

 margin of the wing never yields in an upward direction until 

 the under surface of the pinion makes a backward angle 

 of 4:6° with the horizon, as Marey remarks, is a matter of 

 absolute certainty. This statement admits of direct proof 

 If any one watches the horizontal or upward flight of a large 

 bird, he will observe that the posterior or flexible margin of 

 the wing never rises during the down stroke to a perceptible 

 extent, so that the under surface of the wing on no occasion 

 looks backwards, as stated by Marey. On the contrary, he 

 will find that the under surface of the wing (during the down 

 stroke) invariably looks forwards — the posterior margin of 

 the wing being inclined downwards and backwards ; as shown 

 at figs. 82 and 83, p. 158; fig. 103, p. 186; fig. 85 (abc), 

 p. 160; and fig. 88 (cdefg), p. 166. 



The under surface of the wing, as will be seen from this 



1 Reign of Law "—Good Words, February 1865, p. 128. 



2 History of British Birds. Lond. 1837, p. 43. 



3 " Mechanisme dii vol chez les insectes. Comment se fait la propulsion," 

 by Professor E. J. Marey. Revue des Cours Scientiliques de la France et de 

 I'Etranger, for 20tli March 1869, p. 254. 



