January yt/i, 1 9 19.] PROCEEDINGS. vii. 



available, it was impossible to review the great series of 

 researches made by Joule during his long and busy life but 

 attention would be confined to the first five years (1838-43) of 

 Joule's scientific career which began at the age of nineteen, and an 

 endeavour would be made to trace during this period the gradual 

 growth of Joule's power of experimentation and of philosophic 

 insight. In this, he had been greatly assisted by the able 

 memoir on the work of Joule published by the late Professor 

 Osborne Reynolds in the Memoirs of the Society. 



This period was in some respects the most fruitful and 

 inspiring in Joule's lifetime for it included his remarkable 

 researches on the transformations of energy in the voltaic cell, 

 the dynamo and motor and his first measurement of the 

 mechanical equivalent of heat. 



A brief account was at first given of Joule's researches to 

 improve the electromagnetic engine for the generation of power 

 and of his investigations in electromagnetism. These investiga- 

 tions had an important bearing on his later work, for his electro- 

 magnetic engine, used both as a dynamo and motor, was an 

 indispensable adjunct in his later researches, while the familiarity 

 he had gained in the accurate measurement of the work done by 

 his engine proved later of great value. 



At this stage Joule had appreciated the great importance of 

 accurate measurement of his electrical and mechanical magni- 

 tudes. He had designed a special galvanometer for measure- 

 ment of current in terms of the voltameter of Faraday and 

 adopted definite standards of resistance. It was the use of these 

 standards that made possible his later far-reaching deductions. 



After completing his work on the electromagnetic engine. 

 Joule attacked the problem of the laws of heating of the electric 

 current and proved for the first time that the heating effect was 

 proportional to the square of the current. In this research, he 

 investigated the heat emission in electrolytes as well as in con- 

 ductors and this led to a series of researches in which he traced the 

 various factors to be taken into account to evaluate accurately 

 the energy emitted in an electrolytic cell. He then proceeded to 

 determine the total heat emitted by his voltaic battery for the 

 consumption of one pound of zinc and compared it with the 

 heat developed by the combustion of one pound of zinc in 

 oxygen. After surmounting numerous difficulties, he was able 

 to show conclusively the remarkable fact that the chemical heat 

 of combination was equal to the heat developed by the same 

 chemical change through the intermediary of the voltaic battery. 

 At this early stage, he had thus proved the equality and con- 

 vertibility of chemical, electric and heat energy, and had laid the 

 experimental foundation for the great subsequent generalisation 

 of the conservation of energy. 



