1^22.] Mr, Herapath's Reply to X. 33 



sions are alsomearly as the simple ratio of another set of num- 

 bers ; that set of numbers is the common Fahrenheit tempera- 

 tures ; therefore, within this range h'ttle evidence is gained for 

 or against his theory." To the first sentence I may reply, it is 

 not a set of numbers, but a theorem, I have found. 1 may fur- 

 ther observe, that this theorem I discovered in the year 1815 or 

 1816 ; and was not aware that there was a single experiment in 

 existence to confirm it until Dr. Ure's paper on the tension of 

 vapours appeared in the Phil. Trans, for 1818 ; for I have not to 

 this day seen any of De Luc's papers. I may likewise add that I 

 never attempted to try the truth of itmyself until the fall of 1820, 

 after I had in vain endeavoured to interest the Royal Society in" 

 the proof. This latter part can be confirmed by my cousin, Mr. 

 W. Herapath, who knows I had no apparatus, and assisted me 

 in making thermometers for the purpose in Aug. and Sept. 1820. 

 Dr. Thomson can, I have no doubt, likewise recollect my asking 

 him his opinion about June, 1820, in Queen-square, Westmin- 

 ster, respecting these projected experiments, and the best method 

 of constructing thermometers for high ranges. These facts will, 

 perhaps, satisfy the world, that I have not procured experiments, 

 and formed a theorem to suit them ; but that I first drew from 

 my principles a theorem, in ignorance that there was any thing 

 in existence to confirm it ; then openly proposed it to the Royal 

 Society as the test of my views ; and afterwards, when they 

 would neither try it, nor recommend it to be tried, succeeded in 

 trying and proving it myself. Authenticated circumstances of 

 this kind will, I have no doubt, have their weight with men of 

 liberality, and make a due impression of the soundness of the 

 theory I have expounded, on minds uninfluenced by interested 

 motives in opposing it. 



With respect to the other part of the quotation, the best reply 

 is that contained in p. 100, Annals for Aug. I have there com- 

 puted three experiments, two by De Luc on water, and one out 

 of six or seven by myself, equally consistent, on mercury. The 

 sum of all the deviations of these experiments from my pre-inves- 

 tigated theory, is the one-tenth of a degree of Fahr. ; and the 

 sum of their differences from the old theory, sixteen degrees two- 

 tenths. Thus, instead of the two theories agreeing, as X. says 

 they do, nearly equallywell with experiments, the one wanders 

 162 times further from them than the other. 



These, 1 believe, are the principal objections which X. has 

 advanced against my views. On most of his other observations, 

 particularly that of capacity, which is only a suggestion, it is 

 unnecessary for me to make any remarks. I shall, therefore, 

 with a notice of one more of his ideas, close this paper, and take 

 that leave of him he appears willing to take of me. 



" We cannot,"- observes X. in his last paper, '^ take Mr. H.'s 

 law of temperature as the true law, unless we are sure it holds 

 good at all points in the scale ; but of this we cannot be sure any 



New Series, v o l . 1 1 1 . d 



