496 



Mr. J. P. Joule on the Heat disengaged 



Table VI. — Experiments on the Heat evolved by the Standard 

 Coil. Pile of 4 cells. 



In order to compare the results of the above tables, it now 

 became necessary to ascertain the capacity for heat of the jars of 

 liquid employed in the experiments. This was done in one or 

 two instances by the method of mixtures. The jar along with 

 its contents was heated to a certain point, and then having been 

 immersed in a large can of cold water, the capacity was deter- 

 mined by the decrease of temperature in the former and the in- 

 crease in the latter. I felt, however, that this plan was on several 

 accounts incapable of giving results of extreme accuracy, and 

 had therefore recourse to a method founded upon the law of the 

 development of heat by electricity. The spiral glass tube (fig. 5), 

 filled with mercury, was immersed up to the bulbs aa in the jar 

 whose capacity for heat was to be determined. A current of 

 electricity was then passed through the mercury for a given 

 time, and the heat thereby evolved was observed with the usual 

 precautions. The capacity of the jar and its contents was of 

 course directly proportional to the square of the intensity of the 

 current, and inversely to the increase of temperature. 



Table VII. — Experiments on the Heat evolved by the Mercury 

 Spiral in the jar of Solution of Copper used in the experiments 

 of Table V. Pile of 4 cells. 



