iSogal fingtitution of ffireat Brit 



WEEKLY EVENING MEETING^ 



Friday, Jcanuaiy 24, 1890. 



Sir Frederick Abel, C.B. D.C.L. F.R.S. Vice- 

 in the Claair. 



Professor Dewar, M.A. F.R.S. 3LB.L 



The Scientific Work of Joule. 



(Abstract.) 



Prof. Dewar commenced by remarking that the Royal Institution 

 had been so closely identified with the great workers in physical 

 science that it was impossible to allow the work of Joule, whose 

 researches had produced as marked a revolution in Physical Science 

 as Darwin's in Biology, to pass without recognition in the present 

 series of Friday Evening Discourses. Sir William Thomson, as 

 Joule's friend and fellow-worker to the last, had been invited to 

 undertake the duty, and had agreed to do so ; but at the last moment 

 had been compelled to decline by reason of important official duties 

 in Scotland, and the task had consequently devolved upon him. 



Having given a brief account of Joule's parentage, early life, and 

 education, Prof. Dewar reviewed, as fully as time would permit, his 

 scientific work, which extended over about forty years, and was repre- 

 sented by 115 original memoirs. The first period (1838 to 1843) was 

 distinguished as that in which Joule educated himself in experimental 

 methods, chiefly in connection with electricity and electro-magnetic 

 engines. This work led him in 1840 to his first great discovery, the 

 true law governing the relation between electric energy and thermal 

 evolution, which enabled him later on to account for the whole dis- 

 tribution of the current, not only in the battery in which it is pro- 

 duced, but in conductors exterior to it. Joule was thus led to take up 

 the study of electrolysis. Faraday had already made the discovery that 

 electrolytic bodies could be split up into equivalent proportions by the 

 passage of the same electric current ; Joule saw that there would be 

 great difiiculty in finding out the distribution of the current energy, 

 and accounting for the whole of it. After a laborious research he 

 succeeded in showing that during electrolytic action there was an 

 absorption of heat equivalent to the heat evolved during the original 

 combination of the constituents of the compound body. The prose- 

 cution of his electrical researches rapidly brought Joule on the road 

 to his great discovery of the Mechanical Equivalent of Heat, it being 

 clear from a foot-note to a paper dated 18th February, 1843, that he 

 already had well in hand the study of the strict relations between 

 chemical, electrical, and mechanical effects. 



In working out these laws, it was to be remarked that Joule — in 

 common with most inventors and seekers after new scientific truths — 

 chose perhaps the most difficult means that could have been selected ; 



Vol. XIII. (No. 84.) b 



