ESSAY FOR THE INSTITUTE OF FRANCE. 10 1 



Cornish engine at that time, per grain of coal, is 1431b. raised 

 one foot high, or one-tenth the vis viva due to the combus- 

 tion of coal. 



The duty of a horse per grain of food is 1431b. raised 

 one foot high, or one quarter of the vis viva resulting from 

 the combustion of the food. 



During the interval between the summer of 1844 and 

 the end of 1845, Joule is also deeply engaged in repeating 

 and extending his research made in 1842 on the heat 

 evolved during electrolysis. 



The results of this extended research he communicates 

 in an essay to the French Academy of Sciences, under the 

 motto : — 



" Actioni contraria semper et aequalis est reactio." — Newton. 

 in competition for the prize offered for the best essay on 

 " The Heat of Chemical Combinations." The merit of this 

 ■essay is unquestionable, but Joule seems to have been 

 unaware of the regulations to be observed by the competi- 

 tors for the prize, and to have been too late. The result 

 being that his essay was not published till 185,2, when he 

 .sent it to the Philosophical Magazine. 



In 1846, besides working at the perfection of his 

 apparatus and experiments for obtaining with greater 

 accuracy the mechanical equivalent of heat, Joule is also 

 engaged on two very heavy experimental researches. 



Having completed the research on magnetism, which he 

 had undertaken with Dr. Scoresby, he takes up again " The 

 Effect of Magnetism upon the Dimensions of Iron and 

 Steel." This he had begun in 1841, when Mr. F. D. Arstall 

 suggested to him a new form of electro-magnetic engine 

 based on this, then supposed, effect. The first results were 

 published in Joule's first public lecture (already mentioned). 



