2 THE FLIGHT OF BIRDS 
understand fully what fis 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 
