the true form of Carnot's Function. 389 



peyron expressed by C, and Thomson by the fraction — , " is 



/A 



nothing more than the absolute temperature multiphed by the 

 equivalent of heat for the unit of work/' I have hitherto avoided 

 mentioning this point in my papers ; principally because I have 

 so high an esteem for the labours of the physicist for whom Prof. 

 Thomson claims priority, that I was anxious to avoid even the ap- 

 pearance of wishing to lessen his deserts. But as Prof. Thomson 

 has since then frequently repeated that assertion, — among other 

 places in the paper in the March Number of this Journal, where, 

 in page 215, he calls that theorem " Mr. Joule's conjecture," — 

 I think it necessary to say a few words on the subject. 



Holtzmann established the same formula for the function C 

 in a paper which appeared as early as J 845* ; and Helmholtz, in 

 his pamphlet published in 1847, " On the Conservation of Force," 

 citing Holtzmann's paper, calculated sevei'al values obtained by 

 this formula, and compared them with those arrived at by Cla- 

 peyron in a different manner. But the views upon which Holtz- 

 mann founded his speculations do not agi'ee with the mechanical 

 theory of heat as at present received ; so that after this had been 

 recognized, the correctness of the formula found by him was, 

 naturally, again rendered doubtful. On this account, in a paper 

 communicated to the Berlin Academy in February 1850t, "On 

 the Moving Force of Heat," in which I brought Carnot's pro- 

 position in agreement with the mechanical theory of heat, I 

 again endeavoured to determine his function more accurately. 

 Therein 1 arrived at the same formula as Holtzmann, and I believe 

 that I then, for the first time, correctly explained the principles 

 upon which this formula is based. 



In presence of these facts. Prof. Thomson, to justify his state- 

 ment, says J, "It was suggested to me by Mr. Joule, in a letter 

 dated December 9, 1848, that the true value of /x might be in- 

 versely as the temperature from zero." Against this I must beg 

 to urge, — First, that, as far as I am aware, it is usual, in deter- 

 mining questions of priority in scientific matters, only to admit 

 such statements as have been published. And I believe that this 

 custom ought to be conscientiously adhered to, especially in 

 theoretical investigations ; for it usually requires continued and 

 laborious research in order to give to a thought, after it has been 

 fii'st entertained, and perhaps casually communicated to a friend, 

 that degree of certainty which is necessary before venturing upon 

 its publication. Secondly, that since Thomson does not say that 



* On the Ileat aud Elasticity of Gases and Vapours. By C. Holtzmann. 

 Mannheim, 1845. 



t Poggendorff's Annalen, vol. Ixxix. ; and Phil. Mag. 4th series, vol. ii. 

 J Edinburgh Transactions, vol. xx. p. 279. 



