THE COPLEY MEDALIST OF 1870. 475 



simply as the strength of the current. These inves- 

 tigations were conducted independently of, though a 

 little subsequently to, the celebrated enquiries of 

 Henry, Jacobi, and Lenz and Jacobi, on the same 

 subject. 



On December 17, 1840, Mr. Joule communicated to 

 the Royal Society a paper on the production of heat 

 by Voltaic electricity. In it he announced the law that 

 the calorific effects of equal quantities of transmitted 

 electricity are proportional to the resistance overcome 

 by the current, whatever may be the length, thickness, 

 shape, or character of the metal which closes the circuit ; 

 and also proportional to the square of the quantity of 

 transmitted electricity. This is a law of primary 

 importance. In another paper, presented to, but 

 declined by, the Royal Society, he confirmed this law 

 by new experiments, and materially extended it. He 

 also executed experiments on the heat consequent on 

 the passage of Voltaic electricity through electro- 

 lytes, and found, in all cases, that the heat evolved 

 by the proper action of any Voltaic current is propor- 

 tional to the square of the intensity of that current, 

 multiplied by the resistance to conduction which 

 it experiences. From this law he deduced a number 

 of conclusions of the highest importance to electro- 

 chemistry. 



It was during these enquiries, which are marked 

 throughout by rare sagacity and originality, that the 

 great idea of establishing quantitative relations between 

 Mechanical Energy and Heat arose and assumed definite 

 form in his mind. In 1843 Mr. Joule read before the 

 meeting of the British Association at Cork a paper ' On 

 the Calorific Effects of Magneto-Electricity, and on the 

 Mechanical Value of Heat.' Even at the present day 

 this memoir is tough reading, and at the time it was 



