THE COPLEY MEDALIST OF 1870. 427 



temperature, and the mechanical power which pro- 

 duced it. From the one he derived an equivalent of 

 781.5 foot-pounds; from the other an equivalent of 

 782.1 foot-pounds. The mean of these two very close 

 determinations is 781.8 foot-pounds. 



By this time the labours of the previous ten years 

 had made Mr. Joule completely master of the condi- 

 tions essential to accuracy and success. Bringing his 

 ripened experience to bear upon the subject, he exe- 

 cuted in 1849 a series of 40 experiments on the friction 

 of water, 50 experiments on the friction of mercury, 

 and 20 experiments on the friction of plates of cast- 

 iron. He deduced from these experiments our present 

 mechanical equivalent of heat, just recognised all over 

 the world as ' Joule's equivalent/ 



There are labours so great and so pregnant in con- 

 sequences, that they are most highly praised when they 

 are most simply stated. Such are the labours of Mr. 

 Joule. They constitute the experimental foundation 

 of a principle of incalculable moment, not only to the 

 practice, but still more to the philosophy of Science. 

 Since the days of Newton, nothing more important 

 than the theory, of which Mr. Joule is the experi- 

 mental demonstrator, has been enunciated. 



I have omitted all reference to the numerous minor 

 papers with which Mr. Joule has enriched scientific 

 literature. Nor have I alluded to the important in- 

 vestigations which he has conducted jointly with Sir 

 William Thomson. But sufficient, I think, has been 

 here said to show that, in conferring upon Mr. Joule 

 the highest honour of the Royal Society, the Council 

 paid to genius not only a well-won tribute, but one 

 which had been fairly earned twenty years previously.* 



* Lord Beaconsfield has recently honoured himself and Eng- 

 land by bestowing an annual pension of 200/. on Dr. Joule. 



