196 LORD RAYLEIGH ON FLIGHT. 



advantage of its gustiness. Leaving this subject, the lecturer dis- 

 cussed the general question of the action of the wind on an aeroplane. 

 He first showed one or two experiments illustrating the curious effects 

 that might be obtained from a plane exposed obliquely to wind. In 

 one of these it was seen that a light piece of sheet brass, evenly piv- 

 oted in and nearly tilling up an aperture through which air was issuing 

 under pressure, tended to set itself square to the aperture so as to 

 block it as much as possible, but, if started, it continued to rotate in 

 either direction, emitting a roaring sound. This phenomenon had 

 never been properly explained, nor had the somewhat analogous action 

 of a piece of card, which, when dropped, reached the ground Avith a 

 rotatory motion. As to the pressure of the Avind on a plane surface, 

 if the latter was falling verticallj^ at the rate, sa}", of 4 miles an hour, 

 and also moving horizontally at, say, 20 miles an hour, did the hori- 

 zontal motion make a difference to the pressure that existed at its 

 under surface? It might be argued that it did not; but the argument 

 was fallacious, and the truth was that the horizontal motion nuich 

 increased the pressure under a vertically falling plane, a fact on which 

 depended the possibilit}- of flight, natural and artificial. Lord Ra}^- 

 leigh showed how this point might be illustrated, and even investi- 

 gated, by means of a simple variation of the ordinary windmill. 

 This was a light wheel having six vanes, each of which could be set 

 at any desired angle, and it was used by setting four at a particular 

 angle and ffnding at what angle the other two must be placed so as to 

 compensate the rotation of the wheel produced by the former when it 

 was moved quickly through the air. He next observed that not only 

 was there pressure underneath a bird's wing or an aeroplane, but that 

 the suction above was not an unimportant matter, and he performed 

 an experiment to show the reality of this suction, about which he said 

 there had been some skepticism. Turning to flight on a large scale, 

 he remarked that it was a natural question to ask, Was it possible for 

 a man to raise himself from the ground by working a screw with his 

 own muscular power only? The investigation was not difficult, and 

 the answer was that it was quite impracticable for him to do so. Arti- 

 ficial flight was a question of the speed of the horizontal motion. A 

 bird did not use a revolving mechanism like a screw to propel itself, 

 but he had no doubt that a revolving mechanism was the most suitable 

 for artificial fl^^ing machines. Whether the difficulties of these would 

 be surmounted he did not know, but he was di.sposed to agree with Mr. 

 Maxim that it was mainly a question of some time and much money. 

 Still, he did not think flight would ever be a safe mode of conveyance 

 for those who were desirous of going out for a day's shopping, for it 

 was hard to see how alighting on the ground could ever be rendered 

 quite free from danger. But, as Mr. Maxim once remarked, the first 

 use of flying machines would be for military purposes, and they had 

 not yet succeeded in making war quite safe. 



