322 FRAGMENTS OF 



into the heat evolved by the passage of the currents of in- 

 duction 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 "'mechanical 

 values of heat," deduced from the different series of ex- 

 periments published in 1843, varied widely from each 

 other. The lowest limit was 587, and the highest 1,020 

 foot-pounds, for one degree Fahrenheit 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 engaged 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 he had proved heat to be evolved during the 

 passage of water through narrow tubes; and he deduced 

 from these experiments an equivalent of 770 foot-pounds, a 

 figure remarkably near the one now accepted. A detached 

 statement regarding the origin and convertibility of animal 

 heat strikingly illustrates the penetration of Mr. Joule, 

 and his mastery of principles, at the period now referred 

 to. A friend had mentioned to him Haller's hypothesis, 

 that animal heat might arise from the friction of the blood 

 in the veins and arteries. " It is unquestionable," writes 

 Mr. Joule, " that heat is produced by such friction; but it 

 must be understood that the mechanical force expended in 

 the friction is a part of the force of affinity which causes 

 the venous blood to unite with oxygen, so that the whole 

 heat of the system must still be referred to the chemical 

 changes. But if the animal were engaged in turning a 

 piece of machinery, or in ascending a mountain, I appre- 

 hend that in proportion to the muscular effort put forth 

 for the purpose, a diminution of the heat evolved in the 

 system by a given chemical action would be experienced." 



* Phil. Mag., May, 1840- f See the next Fragment. 



