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 Pls. Iv and v). 
Y;} Vy, P 
PE IP SSS 
| 
4 
Eig. 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 Pls. Iv, v, VI, vi). 
