206 Centenary Commemoration, 1799-1899. [June 6, 



audience that when the blue and yellow of the spectrum were cut off 

 by solutions of litmus and bichromate of potash respectively the com- 

 bination of the remaining red and green was obviously yellow. The 

 lecturer next described Young's way of getting rid of the " false light," 

 that interfered so greatly with the brilliance of the effects when 

 Newton's rings were being obtained by means of two glass plates 

 pressed together, and by analysing the colours from such plates with 

 a prism he exhibited the original of a diagram in Young's book, 

 which indicated the particular rays destroyed by interference. Young 

 was singularly successful in the theory of cohesion and capillarity, in 

 which some of his earliest work was done, and he was the first to 

 deduce an estimate of molecular dimensions from data afforded by 

 that theory. The size of the molecule, according to his calculations, 

 was not very different from that admitted at the present day. In the 

 theory of the tides he made great advances, and in explaining the 

 circumstances which determine whether there shall be high or low 

 water under the moon, he gave the general theory of forced vibrations. 

 His views of heat were very interesting. He had the utmost con- 

 tempt for the idea widely prevalent in his time that it was a separate 

 entity, and expressed the hope that before long philosophers might 

 return to a true conception of its nature as motion. Lord Eayleigh, 

 in concluding his observations on Young, said that possibly he had 

 left the impression that Young knew everything. In fact, it was 

 seldom that he was wrong ; but just to show that he was, after all, 

 human, a passage might be quoted from his book in which he de- 

 clared there was no immediate connection between magnetism and 

 electricity ! Speaking of work which had been done at the Institution 

 by men who held no regular appointment in it, the lecturer noted that 

 Wedgwood, in conjunction with Davy, was the first to produce any- 

 thing that could be called a photograph, while instantaneous photo- 

 graphy, such as was required for rapidly moving objects, was carried 

 out for the first time by Fox Talbot in the laboratory of the Institution. 

 Slides were exhibited illustrative of flying bullets, splashing milk, and 

 breaking soap films, all taken by the electric spark. Towards the 

 close of the lecture Lord Eayleigh showed one famous experiment of 

 Faraday's, the rotation of the plane of polarised light by magnetism, 

 which he observed had acquired a new interest from the recent dis- 

 coveries of Dr. Zeeman. In illustration of Tyndall's work, he instanced 

 the discovery of sensitive flames and their application to acoustical 

 investigation. The analogue of a remarkable optical experiment, from 

 which it appears that there is a bright spot at the centre of the shadow 

 of a circular disc, was exhibited. 



Sir James Crichton-Browne said, 



May it please your Royal Highness, 



The Royal Institution having resolved to mark its Centenary by 

 adding to its roll of Honorary Members the names of some of the 

 most eminent representatives of physical and chemical science on the 



