448 Mr. E. H. Griffiths on 





their work. It is unnecessary to say that in this case there 

 is not the usual doubt as to the thermometric data. In the 

 absence of further details I feel that it would be unbecoming 

 on my part to venture on a criticism of the experimental 

 methods. The result is 4*1905 x 10 7 ergs, expressed in terms 

 of " a thermal unit at 19°*1." 



In endeavouring to make a comparison of the above results 

 the usual difficulty presents itself, viz., the impossibility of 

 expressing them with certainty in terms of any common 

 thermal unit. This does not apply to Rowland's deter- 

 minations or to my own, since the observations extended over 

 temperature-ranges of 5° to 34° and 14° to 26° respectively ; 

 whereas the other observers contented themselves with obser- 

 vations grouped closely about some particular temperature. 

 Fortunately, with the exception of Dieterici's, the difference 

 between the mean temperatures is comparatively small, ex- 

 tending from 11°*5 in the case of Miculescu to 19 0, 1 in the 

 case of Schuster and Gannon. For the reduction of the obser- 

 vations of Miculescu, Joule, and Schuster and Gannon to 

 some common standard, I propose to take the mean of the 

 conclusions of Rowland, Bartoli and Stracciati, and my own 

 as to the changes in the specific heat of water over the range 

 15° to 20°, and the mean of Rowland and Bartoli and Stracciati 

 over the range 10° to 15°, as mine do not extend much below 

 the latter temperature. The results may be expressed as 

 follows : — 



Range 10° to 15°. Coefficient -000414. 

 „ 15° „ 20°. „ -000284 *. 



If, instead of taking the mean of the results of the above 

 observers over these ranges, we adopted the conclusions of 

 any one of them, it would not affect the values of J at 15° in 

 any of the selected cases by more than 1 in 2000. 



The results are shown in the following Table : — 



Values of J expressed in terms of " a thermal unit at 15° C" 



Griffiths 4-198 x 10 7 ergs. 



Schuster and Gannon . . 4*195 x 10 7 „ 



Rowland 4*189 x 10 7 „ 



Joule's later exps. (R)t . 4*182 x 10 7 „ 



Miculescu 4*181 x 10 7 „ 



Joule's later exps. (S) } . 4*174 x 10 7 „ 



* This mean closely approximates to my own coefficient, viz. -000266. 



t In terms of Rowland's air-thermometer. 



X Value resulting from Professor Schuster's determination of the scale- 

 value of Joule's thermometers in terms of the Nitrogen Thermometer of 

 the Bureau International (Phil. Mag. June 1895). 



