CHAPTER XIII 



AERIAL LOCOMOTION 

 The Flight of Birds 



Summary. — Borelli's theory on the mechanism of the flight of birds — 

 Chronography used for determining the frequency of the move- 

 ments of the wing, and the relative duration of the rise and fall 

 — Myography— Method of recording the phases of contraction 

 and relaxation of the wing muscles — Record of the trajectory of 

 a bird's humerus, and the variations in inclination of the surface 

 of the wing— Photographic trajectory of the tip of the wing — 

 Chronophotography as showing the successive attitudes of the 

 bird during the different phases of movement of the wings — 

 Photographs of birds taken from different aspects — Simultaneous 

 chronophotography. 



Of all kinds of locomotion, as existing among verte- 

 brates, that of birds has remained the longest unex- 

 plained. In a rather obscure passage, Borelli cornj)ares 

 the wing action to that of a wedge ; meaning by that 

 ■expression that the surface of the wing bears an 

 oblique relationship to the direction of movement, 

 and that the resistance of the air can be resolved into 

 two separate forces, one of which sustains the weight 

 of the bird, while the other urges it in a forward 

 direction. This interpretation is legitimate in view 

 of the analogy correctly established by Borelli between 

 the propelling action of the wing and that of a fish's 

 tail. 



Being ourselves extremely interested in the me- 

 chanical problem of flight, we have for several years. 



