136 SCIENCE PROGRESS. 



It is evident that this matter requires further investi- 

 gation, for the discrepancies are serious. 



I think, however, there is no doubt as to one con- 

 clusion, viz., that the capacity for heat of water dimin- 

 ishes as its temperature rises, provided the temperature 

 be less than 20 C. 



Dr. Guillaume suggests that the temperature at which 

 the specific heat of water is a minimum should be selected 

 as the standard, but this point is not yet sufficiently estab- 

 lished for the proposal to be carried into effect. 1 



Whatever method be adopted for the determination 

 of J, the numerical results depend upon the value of g. 

 Any error thus introduced is, however, of little con- 

 sequence, since every observer naturally records the value 

 assumed for his own locality, and thus if any error be 

 subsequently discovered the resulting correction is easily 

 applied. 



If the method adopted be an electrical one the in- 

 quirer is dependent on two of the following three con- 

 stants :— 



( 1 ) The electro-motive force of some standard cell. 



(2) The electro-chemical equivalent of some element. 



(3) The value of the ohm. 



The traveller by this route is therefore less independent 

 than the inquirer who adopts a more direct path. 



When, with the assistance of Mr. G. M. Clark, I 

 embarked on this investigation, our desire was not so 

 much to determine the actual value of J as to test the 

 validity of the determinations of the electrical units and 

 to trace the changes in the specific heat of water. I 

 confess that I entertained a hope that our results might 

 be in agreement with Rowland's, and if this had been the 

 case the existing system of electrical measurements might 

 have been regarded as firmly established. As it is, the 

 approximation is sufficient to prove that any residual 

 errors are small. The want of harmony is, however, 



1 1 am glad to hear that Dr. Chappuis has embarked on this investi- 

 gation. 



