Flight of Albatrosses. 



85 



keep on the wing all day with very little exertion. Of course, 

 it is not true sailing, but some word is wanted to distinguish 

 it from the soaring of Vultures, Pelicans, and other birds. 

 For the flight of the Petrels is performed near the surface of 

 the sea and the birds make irregular curves with such sharp 

 turns that their outstretched wings are, when turning, in an 

 almost perpendicular position (see fig. 7). Vultures, when 

 soaring, ascend to a considerable height,, and then wheel 



Fig. s. 



Albatross rising ami turning; to the right. 



round and round in great circles, always keeping their wings 

 hoi izontal. 



Sailing flight depends, of course, upon the principle of the 

 inclined plane. The bird acquires momentum by Hupping 

 its wings and then, holding them extended and motionless, 

 waits until its momentum is nearly exhausted, when it 

 once more propels itself forward as before. In the case 

 of the Sooty Albatross the interval may, under favourable 

 conditions, be about half an hour, and the difficulty is to 

 explain why the friction of the air does not sooner bring the 



