BIRDS. 



471 



This soaring of birds is an oft-discussed problem, and it may be as well 

 to mention it here as anywhere else. Familiar as we are with the law of 

 gravitation, it seems a strange thing that a bird, without a single stroke of 

 the wing, after the 

 first momentum is 

 gained, should be 

 able to go up, up, 

 up, until clear out 

 of sight. We would 

 rather expect it to 

 tumble to the earth 

 as soon as the first 

 impulse was lost. 

 Many are the so- 

 lutions that have 

 been offered, but 

 there is not one 

 that is wholly sat- 

 isfactory. The best 

 advanced is briefly 

 as follows : First, 

 the bird, in mount- 

 ing thus, with rigid 

 pinions, always 

 moves in a spiral ; 

 and second, the 

 soaring never takes 

 place unless there 

 is at least a light 

 breeze. The bird, 

 either by flapping 

 his wines, or start- 



^ A *V 



Fig. 3<J8. — Wood-ibis {Tantalus loculator). 



*&"> 



ing from some elevation, gets his initial momentum, and then the soar- 

 ing begins. Round and round he goes, each complete turn bringing 

 him higher, but at the same time he has drifted away with the wind. 

 As he circles round, at one time his course is with the wind, at another 

 it is directly in the face of it. When going with the wind he allows 

 his body to fall, but holds his wings in such a position that the down- 

 ward motion is converted into forward speed ; then round the turn he 

 goes and faces the wind, and then, like a kite, the breeze carries him 

 up, and to a higher point than on the previous turn. Thus it goes on, 



