( 115 ) 

 WIND AND FLIGHT.* 



BY 



F. W. HEADLEY, m.a., m.b.o.u. 



Part I. 



Designers of flying machines are many ; students of the 

 flight of birds are few, in spite of the fact that there is, 

 in our own country at any rate, a great and growing 

 interest in ornithology. This being so, I pro230se to say a 

 very few words about the general subject of the flight of 

 birds before I try to explain the various ways in whicli 

 they utilise winds and currents of air. 



Air will support a body propelled horizontally through 

 it if only this body moves quickly enough. Speed of 

 movement is an absolute necessity. Any bicyclist knows 

 that the faster he travels, the harder it is to cut his way 

 through the air, even if he does not know that its. 

 resistance increases as the square of his velocity. Sujiposing 

 the figm-e 100 represents the resistance when he is going- 

 at ten miles an hour, it is represented by 400 when he 

 quickens to twenty. This holds of all moderate velocities. 

 At very great speeds the resistance increases even more 

 rapidly. Here, then, is the principle that makes flight 

 possible, for if a flying machine is well built the resistance 

 will come mainly in the form of supj^ort. No sooner had 

 Mr. Maxim's ponderous aeroplane attained a velocity of 

 thirty-six miles per hour than it rose in the air. A bird 

 is built on such perfect lines that the air hinders but little 

 his progress onward. He sets his body, or the plane of 

 his body and expanded wings, at a small angle to the 



* The account I give of soaring in these articles is, I hope, definite and 

 clear. It would certainly not be clear without a general accoiint of wind 

 and flight. This must excuse my recoiaiting again some observations of 

 which I have already published accounts. 



