272 Mr. J. P. Joule on the Heat evolved by Metallic 



was allowed to proceed during twenty minutes, in which time 

 the needle of the galvanometer gradually declined from 55° 

 to 48|°, the mean current being 1 0, 9 Q. The temperature 

 of the liquid had now advanced from 46 0, 6 to 53 0, 95, indi- 

 cating an increase of 7 0, 35. The temperature of the sur- 

 rounding atmosphere was 46 0, 4. 



53. The decomposing cell was now removed again, and 

 the several coils, of which the resistances were, as before, 4*4, 

 5'5, and 7"7, were successively put in its place. The battery 

 now urged through them, 1°'73 Q, l°-48 Q, and l°-22 Q. 



54. In this case 7°'35 4- 0°'55 (for Cor. A) and — 0°'64 

 (for Cor. B) = 7°*26, the heat which was generated in the de- 

 composing jar. 



55. The mean intensity of the current when passing through 



1°"8S -4- 1 0, 73 

 the coil of which the resistance was 4*4, was - 



== 1°*805 Q, but 1°*9 Q when it passed through the decom- 

 posing cell. Hence (4*4 + 3-15*)-^ = 7*17, this, -3-15*, 



leaves 4*02, the amount of obstruction presented by the de- 

 composing cell. 



56. Now we must remember, that when the electric current 

 was passing through the coils, it was urged by the whole in- 

 tensity of the battery ; but that in the case of the decom- 

 posing cell, a part of the intensity of the zinc-iron battery, 

 equal (as I have found by experiment) to 2>\ pairs, or to 

 one sixth part of the whole, is occupied solely in overcoming 

 the resistance to clectrolyzation f of water in the decomposing 

 cell. In order therefore to deduce the true resistance to con- 



4*02 + 3*15 



duction. we must subtract x— — from the obstruction 



6 



4*02; and thus we have 2*83, the true resistance to conduction 



of the decomposing cell. 



57. The latter part of this process is difficult to express 

 clearly, I have therefore drawn a figure to illustrate it. Sup- 

 pose that in fig. 5, 6 represents the intensity of the battery ; 

 the line R 3*15, the resistance of the battery and the con- 

 necting wires ; and the remainder of the line A B, or 4-02 W, 



1-88 1-29 . 1-73 



• From (51. 53.) we have the equations R - = R ^ and R ;v. 7 .7 



_ ...*'** - , whence R = 2-81 and R' = 3-49 : the mean resistance of the 

 ~"R'+4-4' 



battery and connecting wires was therefore 3-1 5. 

 \ Faraday's Experimental Researches, (1 007). 



