WIND AND FLIGHT 147 
Kestrel hovering with motionless wings. The up- 
currents over sun-heated plains seem to have force 
up to an enormous height. In Egypt I once watched 
through my telescope a flock of Storks, ascending 
with wings held rigid till they looked mere specks. 
I wondered how they steered clear of one another, 
there were so many describing mazy, intersecting 
circles. It was just noon, and the day was decidedly 
hot. 
Of course there may be among mountains upward 
currents that are in origin similar to those found 
over level plains. The extraordinary heat of the 
summer of 1911 has been well calculated to produce 
such currents in unusual places. I have a letter 
from Mr. R. C. Gilson that gives most striking 
evidence of this. ‘Lying on my back the other 
day,” he writes (the letter is dated Sept. 16th, 1911, 
“on the summit of the Miirren Schildhorn, a flat- 
topped eminence (about 10,000 feet) with pretty 
steep sides—at all events two opposite sides are 
steep, the mountain is ridge-shaped—I saw a piece 
of paper carried up by the wind, and having no 
tendency to descend, but the reverse. I then noticed | 
another much higher up, then others, an apparently 
indefinite series (the mountain is frequented by 
untidy tourists), of which the farthest that I could 
see were mere silvery specks in the sunshine. How 
high they were it is impossible to say, but I guess 
not far off 1,000 feet above the hill. The weather 
was anticyclonic, almost windless. Presumably the 
elevating forces were convection currents from the 
sun-warmed mountain-side. Where I lay I could 
hardly detect a breeze, but there was always a very 
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