324 FRA GMENTS OF SCIENCE. 



equivalents; the agreement between tliern being far greater 

 than that attained in his first experiments. The mean of 

 them was 802 foot-pounds. From experiments with 

 water agitated by a paddle-wheel, he deduced, in 1845, 

 an equivalent of 890 foot-pounds. In 1847 he again 

 operated upon water and sperm oil, agitated them by a 

 paddle-wheel, determined their elevation of temperature, 

 and the mechanical power which produced 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 labors of the previous ten years had 

 made Mr. Joule completely master of the conditions essen- 

 tial to accuracy and success. Bringing his ripened expe- 

 rience to bear upon the subject, he executed in 1849 a 

 series of 40 experiments on the friction of water, 50 experi- 

 ments 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, justly recognized all over the world as " Joule's 

 equivalent." 



There are labors so great and so pregnant in conse- 

 quences, that they are most highly praised when they are 

 most simply stated. Such are the labors 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 experimental demonstrator, has been 

 enunciated. 



I have omitted all reference to the numerous minor 

 papers with which Mr. Joule has enriched scientific litera- 

 ture. Nor have I alluded to the important investigations 

 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 honor 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 honored himself and England by 

 bestowing an annual pension of 200. on Dr. Joule. 



