272 A NATURALIST IN HIMALAYA 



in every circle and certain conditions on which their 

 sailing flight depends. 



It is soon clear that a circle is not a true circle, but 

 that the kite in sailing round and round traces a 

 succession of pear-shaped figures. These figures for 

 convenience' sake may be called circles. Now the 

 presence of wind appears to be essential to successful 

 circling with increase in height, so it is possible to 

 divide the circle into segments ; one, the windward 

 segment or that portion traced by the bird when 

 moving against the wind, and the other, the leeward 

 segment or that followed by the bird when moving 

 with the wind. Having divided the circle into these 

 two segments, we observe the behaviour of the bird 

 in each of the segments, and from this gain a clue as 

 to the mechanism by which it is sustained. It is 

 understood that the kite is circling, that it is gaining 

 height at every circle, that at one side of the circle it is 

 moving to windward or heading the wind, and that on 

 the other side it is moving to leeward or coming down 

 the wind. 



Thus dividing the circle into a windward and a lee- 

 ward segment, we are able to detect four salient facts. 

 Firstly, we note that the bird on the leeward side 

 makes a much longer sweep than it does on the wind- 

 ward side. It travels over a longer distance. To 

 windward the bird seems cramped for space ; it turns 

 more sharply, while to leeward it circles in a free and 

 easy sweep. In the windward segment it is tracing 

 the sharp apex of the pear, while to leeward it follows 

 a broad open course. 



Secondly, we note that on the windward side of the 

 circle the kite moves at a diminished speed. Away to 



