244 On tlic Capacity for Heat of Water, &c. 



national ohm, it is probable that the error is not there. The recent 

 work on the absolute value of the Clark cell, which is demanding so 

 much attention just now, and which has so far given so many incon- 

 sistent results, makes it very probable that the value of the Clark cell 

 adopted in the present work is in error. If this is so, then, as is 

 pointed out, the value of the Clark cell must be taken as 1*43325 int. 

 volts at 15 C., in order to bring the present series of experiments, 

 involving both the international volt and ohm, into absolute accord 

 with the result by the direct mechanical method of Reynolds and 

 Moorby. 



Having considered the above relationship, the mean value of the 

 mechanical equivalent given by Rowland's experiments between 6 and 

 36 C. is compared with the same mean value from the present series 

 of experiments over the same range. By expressing this latter value 

 in terms of the value of the Clark cell 1 -43325 volts, or as may be 

 said in terms of Reynolds's and Moorby's determination, instead of the 

 original value 1 '43420 volts used in calculation, it comes equal to 

 4'1817 joules. The value obtained from Rowland's corrected curve 

 is 4'1834 joules, which agrees with the present series of experiments 

 to 1 part in 2000. This is a discrepancy so small as to be, if not 

 within the limits of error of these several determinations," at least 

 negligibly small in comparison to the great range covered by the 

 present series of experiments. 



By far the most difficult part of the present series of experiments 

 is the comparison of the absolute value of the mechanical equivalent 

 of heat obtained from these experiments with the values obtained by 

 the electrical method used by Griffiths, and by Schuster and Gannon, 

 even when our several results are expressed in terms of the same values 

 of the units used. There is every reason to believe that the values 

 of the resistance standards used in the present work were the same as 

 those used by both these investigators. It is also highly probable 

 that the values of the Clark cells in the present series of experiments 

 were in correct agreement with all the best results that have been 

 obtained in setting up this electro-chemical combination. It is probable 

 that the difference in the values obtained by Griffiths, and by Schuster 

 and Gannon, from the value obtained in the present series of experi- 

 ments must be attributed not to these, but to the radical difference in 

 the methods of calorimetrv. 



