THE POSSIBILITY OF SOARING IN HORIZONTAL WIND. 211 
see why the best soaring is done in steady winds, The answer 
is, the bird is less liable to lose its vortices by a sudden gust and 
have to take a flap or two to balance itself on a fresh pair. The 
difference between flying and soaring is that the air in contact 
with the underside of the wing is moving towards the bird’s head 
when soaring and towards the tail when flying. A soaring bird’s 
wing is a shield dividing two currents of air moving in contrary 
directions. The vortex draws towards the shield and pushes it 
into the low pressure above the wing. 
There is a very similar experiment described at pages 79, 80, of 
this Society’s Journal for 1893, but I then failed to see the true 
cause of the phenomenon and thought the air currents were those 
shown in the flying wing (Plate 17, fig. 1) whereas the currents 
were those of the soaring wing. 
Mr. Chanute says that, ‘Dr. Thomas Young, the great physicist, 
showed in 1800 that a curved S-like surface suspended horizontally 
by a thread advanced against an air jet impinging upon its upper 
surface.” If this S-like surface proves to be like Plate 17, fig. 16, 
and he explains the cause to be the vortex shown therein, it is only 
another proof that there is nothing new under the sun. The 
turn-up tail is now being experimented with, as I think it provides 
automatic stability in a fore and aft direction. 
Having experienced much of the monotonous process of repair- 
ing broken models, I have now devised and am using a method of 
experimenting that practically enables me to avoid all breakages. 
The apparatus used is well shown in Figures 17 and 18, which 
I think will advance the art of aérial navigation more than 
any amount of laboratory experiments. The two poles are twenty- 
four feet high and forty-eight feet apart. There is a cord between 
the tops of the poles, and the string of the soaring kite is tied to 
the middle of the cord at a sufficient height to prevent it striking 
the ground. I stand to leeward of the poles and start the soar- 
ing kite at a positive angle, it then flies as an ordinary kite to 
near the zenith. The vortex then forms under the curved — 
