324 FRAGMENTS OF SCIENCE. 
equivalents; the agreement between them being far greater 
than that attained in his first experiments. The mean of 
them was 802 foot-ponnds. 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, nas 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. 
