WIND AND FLIGHT 145 



round a little below me. In hot countries it takes 

 place over wide plains where there are no hills 

 near. I have never seen or heard of it under such 

 conditions in cold, northern regions. Nor have I seen 

 any attempt at it over the sea. Gulls are no mean 

 performers at soaring, and they may frequently be 

 seen circling in fine style over cliffs. The fact that 

 they do not soar out at sea, and that they frequently 

 do where there are cliffs of any height, suggests the 

 secret of the whole thing. The bird when soaring 

 is lifted and maintained by an upward-trending 

 wind. At sea, in our northern latitudes, there are no 

 up-currents, or none of strength sufficient to make 

 soaring possible. Sir Hiram Maxim is able to detect 

 up-currents and down-currents of air that leave 

 smooth or ruffle our comparatively cold northern 

 seas.* It would be folly to deny their existence 

 without very definite evidence. It is very difficult, 

 however, to believe that they are currents of much 

 strength. The water far away from the Tropics 

 does not get heated sufficiently to cause a rapid 

 upward movement of air. Were the up-currents 

 which Sir Hiram Maxim has detected of any force 

 and lifting power, would not the Gull and the Shear- 

 water, quick as they are to avail themselves of any 

 little up -draught due to steamer or to waves, hasten 

 to make use of them ? I am quite aware that I am 

 here guilty, technically, of a petitio principii. I 

 wish to show that soaring depends on up-currents 

 of air, and I use the fact that Gulls do not soar at sea 

 — at any rate not over our northern seas — as evidence 

 that there are no strong up-currents. The reader 



* Artificial and Natural Flight, p. 16. 



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