THE COPLEY MEDALIST OF 1870 445 



inrestigations were conducted independently of, though 

 a little subsequently to, the celebrated inquiries 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 Vol- 

 taic electricity. In it he announced the law that the calo- 

 rific effects of equal quantities of transmitted electricity are 

 proportional to the resistance overcome by the current, 

 whatever may be the length, thickness, shape, or char- 

 acter of the metal which closes the circuit; and also pro- 

 portional 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 Eoyal 

 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 electrolytes, and found, in all cases, that the heat 

 evolved by the proper action of any Voltaic current is pro- 

 portional to the square of the intensity of that current, 

 multiplied by the resistance to conduction which it expe- 

 riences. From this law he deduced a number of conclu- 

 sions of the highest importance to electro-chemistry. 



It was during these inquiries, which are marked 

 throughout by rare sagacity and originality, that the great 

 idea of establishing quantitative relations between Me- 

 chanical 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 Calo- 

 rific 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 written it must have 

 appeared hopelessly entangled. This, I should think, was 



