2 THE FLIGHT OF BIRDS 



understand fully what his methods are. But what- 

 ever the difficulty of learning from him, the bird had 

 certainly much to teach. Such a past master in 

 the art of flying must needs be able to give some 

 hints to the man whose ambition it was to discover 

 the ideal design for an aeroplane. 



And so the question " How does a bird fly ? " 

 became one that had an interest not only for 

 ornithologists. Those who gave it any thought 

 soon found that it involved a number of problems. 

 First comes the question how the yielding air can 

 support a heavy body when gravity is tugging it 

 downwards. Then, of no less practical interest 

 is the question, how the bird maintains his equi- 

 librium, or recovers it if for the moment he happens 

 to lose it. How does he move his wings so that 

 they may at once propel and support him ? How 

 does he steer ? How is it that the small bird is 

 able to start so easily from the level ground ? 

 What of the easier but important problem of alighting 

 without jar ? How is it that the bird, big or small, 

 is able to treat with contempt the sudden gusts 

 and eddies that the boldest aviator fears ? Does 

 the bird ever gain advantage from the unequal 

 velocity of the wind ? Does he search for up-currents 

 and get them to lift him ? 



Resistance of Air. 



The first of these problems was solved by Sir 

 Isaac Newton. By means of an experiment, that 

 may well astonish us if we bear in mind how 

 imperfect were the appliances that he had at his 

 disposal, he demonstrated the peculiar property of 



