624 



BIRDS. 



it, surpasses it, outraces it ; is the air, conscious of itself, conquering 

 itself, ruling itself " 



Ruskin has compared the flight of a bird to the sailing of a boat. " In 

 a boat, the air strikes the sail ; in a bird, the sail strikes the air ; in a 



Fig. 222. — Wings coming down. (From Marey.) 



boat, the force is lateral, and in a bird downwards ; and it has its sail 

 on both sides." But, as he says, the sail of a boat serves only to carry 

 it onwards, while wings have not only to waft the bird onwards, but to 



Fig. 223. — Wings completely depressed. (From Marey.) 



keep it up. To carry the weight of the bird the wings strike vertically, 

 to carry the bird onwards they strike obliquely ; sometimes the direction 

 of the stroke is more vertical, and then the bird mounts upwards • 



