288 SCIENCE PROGRESS 



Professor. It was the gift to the University of the Chancellor, 

 the seventh Duke of Devonshire. Laboratory training in 

 Physics was almost unknown. Carey-Foster had established 

 classes in University College, and Clifton was in charge of the 

 Clarendon Laboratory at Oxford. Maxwell gathered round 

 him a few senior students, among them Chrystal, W. D. Niven, 

 Garnett, and Donald Macalister ; but the Laboratory, though 

 equipped with a large collection of lecture-room and similar 

 apparatus, was not laid out for the training of the ordinary 

 undergraduate. 



Rayleigh, with the help of his demonstrators, set himself 

 to alter that. Classes in Practical Physics were organised, 

 and the senior men, encouraged by the example of the Professor, 

 began to undertake physical research work. For himself he 

 commenced that great series of Electrical Measurements which 

 have formed the real starting-point of the system of Electrical 

 Units to which the progress of Electrical Engineering is so 

 greatly due. The unit of electrical resistance, the " ohm ' 

 had been first realised in concrete form by the work of Maxwell 

 at King's College, but further investigation on the Continent 

 had thrown some doubt on his result, and Rayleigh and Schuster 

 undertook to solve the uncertainty. 



In his later work he had the assistance of his sister-in-law, 

 Mrs. Sidgwick, and with her carried out his classical measure- 

 ments on the Silver Voltameter and the Latimer Clark Cell, 

 thus establishing definitely the units of resistance, current, 

 and electromotive force. 



These researches illustrated in a marked degree Lord 

 Rayleigh's genius as an experimental physicist. The appara- 

 tus employed, except when high precision was required, was of 

 the simplest, that which came nearest to hand was utilised ; 

 and, whether at the Cavendish Laboratory or at his private 

 laboratory at Terling, visitors were astonished at the means by 

 which results of surprising accuracy, accuracy which has only 

 been further substantiated by more elaborate research, were 

 reached. 



During this same time there appeared also some remarkable 

 short papers on optical questions, dealing with the resolving 

 power of optical instruments and cognate matter. To him 

 we owe much of the fundamental work connecting the aperture 

 of an optical instrument with its power to distinguish the small 



