LORD RAYLEIGH ON FLIGHT.^ 



The first Friday evening meeting for this season of the members of 

 the Royal Institution took place last night, when Lord Rayleigh deliv- 

 ered a discourse on '"Flight." The Duke of Northumberland was in 

 the chair, and among the large audience were Lord and Lady Kelvin, 

 Sir Frederick Bramwell, Mr. A. J. Balfour, Sir Frederick Abel, Sir 

 William C'rookes, Sir James Crichton-Browne, Professor Dewar, Mr. 

 Justice Stirling, Dr. J. H. Gladstone, Mr. Hiram Maxim, and Sir 

 H. T. Wood. 



Lord Rayleigh lirst considered the question what people generally 

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

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

 machine l)ig enough to carry a man by whom it could be controlled. 

 The main problem of the llA'ing machine was the problem of the aero- 

 plane. What were the forces that acted on a plane exposed to the 

 wind? This was also the vital problem of kites, of which he men- 

 tioned some of the practical applications ])y Franklin, Archibald, 

 Baden-Powell, and others; ])ut kites were always anchored to the 

 ground, and as soon as we cast ourselves adrift from the ground the 

 problem l)ecame difficult, for it was then necessary to consider how 

 maintenance in the air could ])e 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 

 itself with l)ut little flapping of the wings? There had been much 

 discussion about this point, often foolish because of misunderstand- 

 ings between the disputants. However, the science of mechanics 

 enabled it to ])e laid down with certainty that a bird could no more 

 maintain itself without motion of the wings in a uniform wind mov- 

 ing horizontally than in air at perfect rest. It was entirely a question 

 of relative motion. If, then, a bird was seen to be maintaining itself 

 without flapping it was certain the air was not moving horizontally and 

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

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

 supposed. In other cases where it w^as difficult to imagine the exist- 

 ence of such currents an explanation might be sought in the nonuni- 

 formity of the wind, for it was mechanically possible for a bird just 

 at the point of transition between two diflerent strata of wind to main- 

 tain its position by taking advantage of the different velocities. The 

 albatross, he believed, did so. Langley, again, had pointed out how 

 the bird could turn to account the internal work of the wind by taking 



^From London Times, January 20, 1900. 



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