232 MOVEMENT 



were not only fully confirmed, but this new method 

 also completely explained the movements of flight. 



In this research, as in those on different kinds of 

 locomotion, it was necessary to combine several 

 methods, each with its own particular object. Direct 

 registration, with its continuity of record, was always 

 made use of when it was necessary to determine 

 the frequency and duration of a given movement 

 of a part of the body. Chronophotography was 

 useful when a general idea of the movement was 

 desired ; it was also the only means by which 

 the movements of an isolated . point could be ex- 

 pressed, when the movement was not accompanied by 

 the development of a certain amount of force. An 

 example of this kind may be seen in the trajectory 

 described by the extremity of a wing. It is impossible 

 to apply a registering apparatus to the end of 

 a flexible feather ; but the true interest of chrono- 

 photography lies in the fact that it can provide a 

 complete picture of a bird, in the various attitudes it 

 assumes during the act of taking a stroke with its wings. 



Successive Photographs of Birds taken on the Wing. — 

 If a white bird, brightly illuminated by the sun, is 

 photographed in series as it crosses in front of a dark 

 background, its various attitudes will be clearly seen. 

 In these photographs the bending of the wings due 

 to the resistance of the air is usually quite evident, 

 and it expresses in a striking manner the force with 

 which the wing is moved ; if one tries to reproduce the 

 same degree of bending by mere manual force one is 

 quite astonished at the amount necessary. This curving 

 of the feathers may be observed in all kinds of 

 birds, but in different degrees according to the 

 flexibility of the wings ; thus, for instance, it is very 

 pronounced in the case of a flying heron, just when 

 the wing reaches the mid phase of descent (Fig. 163). 



