446 FRAGMENTS OF SCIENCE 



the reason why Faraday advised Mr. Joule not to submit 

 the paper to the Koyal 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 

 demonstrated, experimentally, that the mechanical power 

 exerted in turning a magneto-electric machine is converted 

 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 ob- 

 tained 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 deter- 

 mination, it is not surprising that the "mechanical 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 temperature. 



One noteworthy result of his inquiries, which was 

 pointed out at the time by Mr. Joule, had reference to 

 the exceedingly small fraction of the heat actually con- 

 verted into useful effect in the steam-engine. The thoughts 

 of the celebrated Julius Robert Mayer, who was then en- 

 gaged in Germany upon the same question, had moved 

 independently in the same groove; but to his labors due 

 reference will be made on a future occasion.' In the 

 memoir now referred to, Mr. Joule also announced that 

 lie had proved heat to be evolved during the passage of 

 water through narrow tubes; and he deduced from these 



* "Phil. Mag.," May, 1845. ' See the next Fragment. 



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