

llaml Institution of feat Britain. 





WEEKLY EVENING MEETING. 



Friday, January 19, 1900. 



His Grace The Duke of Northumberland, K.G., President, 

 in the Chair. 



The Et. Hon. Lord Eayleigh, M.A. D.C.L. LL.D. F.R.S. M.B.I. 



PROFESSOR OF NATURAL PHILOSOPHY E.T. 



Flight. 



Lord Rayleigh first considered the question what people generally 

 meant when they spoke of a flying machine, and concluded that size 

 had a great deal to do with their conception, which was usually of 

 a machine big enough to carry a man by whom it could be con- 

 trolled : otherwise the flying machine had been invented long since 

 by Penaud. The main problem of the flying machine was the 

 problem of the aeroplane. What were the forces that acted on a 

 plane exposed to the wind ? This was also the vital problem of 

 kites, of which he mentioned some of the practical applications by 

 Franklin, Archibald, Baden-Powell, and others ; but kites were 

 always anchored to the ground, and as soon as we cast ourselves 

 adrift from the ground the problem became essentially different, for 

 it was then necessary to consider how maintenance in the air could 

 be managed. Now some birds seemed to maintain themselves in the 

 air with little effort. What was the nature of the " soaring " or 

 " sailing flight " by which a big bird maintained himself with but 

 little flapping of the wings ? There had been much discussion about 

 this point, often foolish because of misunderstandings between the 

 disputants. However, the science of mechanics enabled it to be laid 

 down with certainty that a bird could no more maintain himself 

 without motion of the wings in a uniform wind moving horizontally 

 than in air at perfect rest. It was entirely a question of relative 

 motion. If, then, a bird was seen to be maintaining himself without 

 flapping, it was certain the air was not moving horizontally and 

 uniformly. But there might be rising currents of air upon which he 

 was supported, and these were much more common than was often 

 supposed. In other cases where it was difficult to imagine the 

 existence of such currents, an explanation might be sought in the 

 non-uniformity of the wind. For example, it was mechanically 

 possible for a bird just at the point of transition between two 

 different strata of wind to maintain its position by taking advantage 

 of the different velocities. The albatross, he believed, did something 

 of this sort. Langley, again, had pointed out how the bird could 

 turn to account the internal work of the wind by taking advantage 

 of its gustiness. Leaving this subject, the lecturer discussed the 

 general question of the action of the wind on an aeroplane. He first 

 Vol. XVI. (No. 94.) b 



