MOTIVE POWER 



43 



the forward-downward movement as giving the 

 required incline I wish to lay stress, because treatises 

 on flight do not, as far as I know, recognize this way 

 of obtaining the downward slope, but speak only of 

 the depressing of the front margin relatively to the 

 back (see Pis. iv and v). 



Fig. 17. 



Gulls flying (after Marey). A. — 25 photographs per second. 

 B. — 50 per second. 



I am now going to describe more in detail the 

 different phases of the stroke. For this I must 

 depend to some extent on Professor Marey's photo- 

 graphs. Other photographers, myself among them, 

 taking snapshots, have caught the various wing 

 positions. He shows us the various phases in series : 

 they follow one another at the rate of 25 or of 50 

 per second (see fig. 17 and Pis. iv, v, vi, vn). 



