These experiments, though they have continued over a considerable period of time, are, unfortunately, by no means conclusive in results. I may as well explain how and why I conducted them. Actual trials of aërial propellers have not very often been made, or perhaps I should say that the results of such trials have not often been published. This latter may be for two reasons : 1st, that inventors wish to keep the results of their investigations to themselves, which, though somewhat selfish, is but natural. 2nd. The results may be such that the experimenters do not think them worth recording. I have considered whether I should not comply with this second reason, and simply look upon the results of my work as negative and not worth recording.

The soap bubble and the projectile illustrate the two opposite extremes of mechanical flight.

The two greatest hindrances to the solution of this problem have always been the balloon and the screw propeller.

People pick up this and that old device, and fancy that a merely new combination will answer their purpose. The balloon is one such device, having one chief function— that of flotation. Balloon troubles and risks are so well-known to every member of this Society that they need no description. The very obvious schoolboy device of elongating the bulb and driving it end-on with a screw propeller has only resulted in the attainment of a feeble speed, not hitherto exceeding 10 miles an hour in a dead calm.

The number of successful glides accomplished by Mr. Wilbur Wright and his brother, with their double-decked gliding machine in America, would seem to be a proof of the value of those careful preliminary experiments which it has been the custom of these intrepid aviators to originate. After their first experiments, made with gliding machines in 1900 and 1901, they undertook laboratory experiments for the purpose of determining the amount and direction of the pressures produced by the wind upon plane and arched surfaces exposed at various angles of incidence; upon the results of these experiments a new pattern machine was constructed in 1902.