424 FRAGMENTS OF SCIENCE, 



written it must have appeared hopelessly entangled, 

 This, I should think, was the reason why P"araday 

 advised Mr. Joule not to submit the paper to the 

 Royal Society. But its drift and results are summed 

 up in these memorable words by its author, written 

 some time subsequently : ' In that paper it was demon- 

 strated experimentally, that the mechanical power 

 exerted in turning a magneto-electric machine is con- 

 verted into the heat evolved by the passage of the 

 currents of induction through its coils ; and, on the 

 other hand, that the motive power of the electro- 

 magnetic engine is obtained at the expense of the heat 

 due to the chemical reaction of the battery by which it 

 is worked.' ! It is needless to dwell upon the weight 

 and importance of this statement. 



Considering the imperfections incidental to a first 

 determination, it is not surprising that the 'mechani- 

 cal values of heat,' deduced from the different series 

 of experiments published in 1843, varied widely 

 from each other. The lowest limit was 587, and 

 the highest 1,026 foot-pounds, for 1 Fahr. of tempera- 

 ture. 



One noteworthy result of his enquiries, which was 

 pointed out at the time by Mr. Joule, h^d reference to 

 the exceedingly small fraction of the heat actually 

 converted into useful effect in the steam-engine. The 

 thoughts of the celebrated Julius Eobert Mayer, who 

 was then engaged in Germany upon the same question, 

 had moved independently in the same groove ; but to 

 his labours due reference will be made on a future 

 occasion. 2 In the memoir now referred to, Mr. Joule 

 also announced that he had proved heat to be evolved 

 during the passage of water through narrow tubes ; and 



1 Phil. Mag., May 1845. See the next Fragment. 



