BIRDS AND THE WIND McMILLAN 363 



tained its true direction and velocity. A quartering wind on the 

 ground will, in all probability, be a direct tail wind aloft. Is it not 

 possible, therefore, that bird students have actually observed that 

 migrants prefer tail winds ? 



Perhaps it is true that they do. Perhaps it is only fancy born of 

 the writer's own natural desire for a clear sky and a tail wind. 

 Whether true or false, there is one fact that is certain : the winds are 

 there for the birds to use. All they have to do is choose. Sir 

 Napier Shaw in his book, The Air and Its Ways, has likened the cir- 

 culation of the atmosphere to a steam engine run by the heat of 

 the sun. The spinning cyclonic and anticyclonic areas he has called 

 the flywheels of that engine. In his own words, he says, "the con- 

 stituent parts of the flywheel at any time are the natural airways of 

 the world." He was speaking of aviation when he made the state- 

 ment but, in the opinion of the writer, he might better have spoken 

 of the birds. Perched on the spinning wheels and the whirling 

 belts, they are riding the natural flyways of the world. 



