366 



NATURE 



[July io, 1919 



from the point of view of a text-book and also 

 as a record of original research. In general 

 dynamics we owe to him great extensions in the 

 application of the principle of reciprocity, and re- 

 searches on the general theory of vibrations of 

 dynamical systems and on the partition of energy. 

 All these researches present a perfect amalgama- 

 tion of physical principles and mathematical 

 analysis ; the physics guides and directs the 

 analysis, while the analysis gives definiteness and 

 point to the physics. 



On the more purely experimental side we recall 

 Rayleigh's classical determination, made mostly 

 in co-operation with Mrs. Sidgwick when he was 

 Cavendish professor, of the absolute measure of 

 the fundamental units of electricity. Among the 

 experimental researches is the one by which he is 

 most widely known and in which he perhaps 

 opened up the newest ground — the discovery of 

 argon. As an inadequate estimate of the part 

 Rayleigh took in this discovery is not uncommon, 

 it may be as well to recall the facts relating to 

 it. In a letter to Nature in 1892 he said he had 

 been much puzzled by the difference between the 

 density of the nitrogen obtained from the air and 

 that obtained from compounds of nitrogen. The 

 latter was always considierably lighter. He fol- 

 lowed this up by a paper, published- in 1894, in 

 which he showed that there was no variation in 

 the density of nitrogen prepared from different 

 nitrogen compounds, so that this must be 

 regardeid as true nitrogen, and that the heaviness 

 of the nitrogen obtained from the air must be 

 due to the presence of a heavier gas ; it was 

 shown in this paper that this gas could not be any 

 of the gases known to chemists. This view was 

 not universally accepted by chemists, convincing as 

 the evidence was, for it seemed to some of them in- 

 credible that the atmosphere contained large quan- 

 tities of a gas which had quite escaped dilution. 



In his search for this gas Rayleigh was for- 

 tunate enough to secure the co-operation of 

 Sir William Ramsay, and their joint work was so 

 successful that at the meeting of the British Asso- 

 ciation in Oxford in 1896 they were able to 

 announce the discovery that the air contained 

 about \ per cent, of a new gas, argon. This 

 gas proved to have remarkable properties and 

 to belong to a new family in the chemical 

 elements, many other members of which were 

 afterwards discovered by Sir William Ramsay. 

 Though both shared in running down the hare, 

 it was Rayleigh alone who started it, and this 

 not by a happy accident, or by the application of 

 new and more powerful methods than those at 

 the disposal of his predecessors, but by that of the 

 oldest of chemical methods — the use of the 

 balance. 



A remarkable feature of Rayleigh's experi- 

 mental work was the simplicity of the apparatus 

 with which the results were obtained ; it has been 

 said of him that he needed nothing for his experi- 

 ments but some glass tubing and a few pieces 

 of sealing wax. The many Continental and 

 American physicists who visited Terling were 

 NO. 2593, VOL. 103] 



filled with amazement that such important results- 

 could have been obtained with such simple 

 apparatus. His example shows that, provided 

 you can "mix your colours with brains," there 

 are still regions in physics in which good work 

 can be done with modest appliances ; at the same 

 time, it is true that there are other regions in 

 which time would be wasted unless powerful and 

 elaborate appliances were available. 



Though Rayleigh's activities were mainly 

 engaged with research, he did very important 

 work in other fields. He held from 1879 to 1884 

 the Cavendish Professorship of Experimental 

 Physics at Cambridge — there seemed something 

 peculiarly appropriate in his holding a professor- 

 ship with this title, for the work of Cavendish 

 and Rayleigh had many characteristics in 

 common. While at Cambridge he not only made 

 the determinations of electrical constants already 

 alluded to, but in conjunction with Glazebrook and 

 Shaw he also organised the teaching of theoretical 

 and practical physics, and made for the first time 

 the laboratory take an integral part in the training 

 of students of science. The writer, who was a 

 pupil of his at Cambridge, remembers well the 

 assistance he gave to those working in the labora- 

 tory, and how greatly a talk with him cleared up 

 one's notion of a subject and helped to overcome 

 difficulties. 



Rayleigh was for eighteen years professor of 

 natural philosophy at the Royal Institution, and 

 was scientific adviser to the Elder Brethren of 

 Trinity House. He had been secretary and after- 

 wards president of the Royal Society, and since 

 1908 Chancellor of the University of Cambridge. 

 He took the keenest interest in the formation and 

 development of the National Physical Laboratory ; 

 he was chairman of the executive committee from 

 the beginning until a few months before his 

 death, and his interest, advice, and influence 

 have played a very large part in securing the 

 success of that institution. He was a member of 

 the Advisory Council for Scientific and Indus- 

 trial Research, and as chairman of the Committee 

 for Aeronautics rendered great service to the 

 progress of aviation. Throughout the war his 

 advice was of much assistance to many com- 

 mittees engaged in the applications of science to 

 naval and military purposes. 



Though Rayleigh disliked even more than most 

 men the loss of time inseparable from attendance 

 at committees and meetings, he took his full 

 share of such work, and it has been a great thing 

 for British science to be able to call to its councils 

 a man whose judgment was never influenced by 

 prejudice or by a shadow of self-seeking. 



J. J- T. 



John William Strutt, third Baron Rayleigh, 

 was born in Essex on November 12, 1842, 

 and succeeded his father in the title in 

 1873. He was educated at Trinity College, Cam- 

 bridge, taking his degree as Senior Wrangler in 

 1865. His immediate neighbours in the Tripos' 

 list were Prof. Alfred Marshall and Mr. H. M. 



