2 Reynolds and Moorby, Equivalent of Heat. 



tion of the circumstances and motive which led to the 

 undertaking. 



In the experimental comparison of physical quantities 

 in different modes, such as heat and work, the. measured 

 results depend not only on the aptitude and foresight of 

 the experimenter and on the particular units employed, but 

 involve fundamentally the standards to which the units 

 are referred. Thus, in a repetition of the experiments, 

 however accurate, the results should not agree unless the 

 standards employed are the same. 



Now Joule's standard of temperature-measurement was 

 the scale of his thermometer ib), which is now in the 

 custody of the Society, and which has not been used in any 

 other determination. 



Other determinations have been made by various 

 observers with various thermometers, and the results are 

 various which, though none of them differ by more 

 than I % from Joule's values — 772-69 (1849), 772*55 

 (1878) — , are on the average higher than Joule's. And, 

 as the result of two researches (Rowland and Griffiths), 

 there had, before 1890, been serious proposals, published 

 in the Transactions of the Royal Society, to adopt the 

 number yjZ instead of J or 772. '■ 



As a member of this Society, the author felt strongly 

 averse to this proposal, and not only so, but, from a study 

 of the published papers, convinced, himself that, notwith- 

 standing the improved laboratory conveniences, the 

 methods and means by which these later results were 

 obtained, were, quite apart from Joule's wonderful aptitude, 

 in no way comparable with those of Joule ; still he did not 

 then feel competent, even had he been able to do so, to 

 attempt a verification of Joule's results ; for it seemed to 

 him a mere impertinence to publish results either as 

 verifying or correcting those already obtained except 

 with the fullest assurance that the requisite means, aptitude, 



