I hold that in the flight of the soaring birds (the vultures, the eagles, and other birds which fly without flapping) ascension is produced by the skillful use of the force of the wind, and the steering, in any direction, is the result of skillful manoeuvres; so that by a moderate wind a man can, with an aeroplane, un- provided with any motor whatever, rise up into the air and direct himself at will, even against the wind itself.