WIND AND FLIGHT 145 
round a little below me. Jn 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. Atsea,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 principw. 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. 
