io 4 ANIMALS AT WORK AND PL A Y 



wing as they swung on in great circles till they 

 were lost to sight. It was an instance, if such 

 were wanted, establishing beyond doubt the power 

 of birds to sail without flapping their wings or 

 gradual loss of height for long periods against the 

 wind.' Until recently, however,^ instances establishing 

 this fact were very much wanted. Because they 

 would not understand how it could be done, 

 many people denied that it could be done, and 

 like the Professor in the Water Babies, who called 

 Tom a holothurian and a cephalopod because he 

 would not admit that he was wrong, they invented 

 all sorts of ingenious theories to account for the 

 c appearance ' of soaring, or to show that though 

 birds did float in air it was not soaring but 

 something else. One, that soaring birds ' imparted 

 a vibratory movement to their feathers,' which they 

 can do, but only use it to dry them after wash- 

 ing or when they are frightened ; another, that the 

 air in the bird's bones and air vessels expanded 

 and kept them up like a balloon ; and a third 

 and more probable one, that they only soared 

 when there were upward draughts of air, on which 

 they floated like burnt paper over a chimney-pot. 

 This was quite satisfactory so far as it went, and 

 where the existence of an upward current could 

 be proved. A good example was seen by the 



