MECHANICAL VALUE OF HEAT. 6$ 



the resistance. The results he obtains give for the work 

 necessary to raise lib. of water I degree Fahrenheit, quan- 

 tities which lie between 1,026 and 587 lbs. raised one foot. 

 Upon which he says : — " The foregoing are all the experi- 

 ments I have hitherto made on the mechanical value of 

 heat. I admit there is considerable difference between 

 some of the results, but not, I think, greater than may be 

 referred with propriety to mere errors of experiment. I 

 intend to repeat the experiments with more powerful and 

 more delicate apparatus. At present we shall adopt the 

 mean result of the thirteen experiments given in this paper, 

 and state generally that" 



" The quantity of heat capable of increasing the 



temperature of a pound of water one degree of Fahrenheifs 



scale is equal to, and may be converted into, a mechanical 



force, capable of raising 8 58 lbs., to a perpendicular height 



of one foot." 



This result is the climax of Joule's researches. For 

 although he was immediately able, by using simpler means, 

 to attain greater accuracy in the determination of the 

 mechanical equivalent of heat ; this was of small importance 

 compared with the philosophical insight which resulted 

 from the comprehensiveness and sequence of his in- 

 vestigation. 



Commencing with the electro-magnetic engine, and 

 discovering the measure of the electric action equivalent to 

 the work done, then showing that the heat developed in a 

 conductor has also an equivalent in the same measure of 

 electric action, and further that the heat developed in the 

 cells of a battery has an equivalent in the same action when 

 proper allowance is made for secondary actions ; and so 

 discovering, by means of this measure of electrical action, 

 F 



