122 Dr. Joule on the History of the Dynamical Theory of Heat. 



mesure et la representation de cctte diminution de chaleur." In 

 p. 389 be gives a Table of tbe quantity of mecbanical effect pro- 

 duced corresponding to tbe loss of temperature of steam on ex- 

 pandiug. From tbis it appears tbat 1° Cent, corresponds with 363 

 kilogrammes raised to tbe beight of 1 metre. At p. 403 be states, 

 " Je bornerai la mes reflexions sur un sujet dont cbacun saura ap- 

 prdcier Fimportance. Du calorique qui est employe par Tindustrie 

 k produire de la force, et aux usages domestiques, une faible partie 

 seulement est utilisee ; une autre quantite bien plus considerable, 

 et qui pourrait suffire a creerd'im menses valeurs et a augmenter 

 d'autant la ricbesse nationale, se trouve absolument perdue." 

 From tbe above extracts, it will be seen that a great advance 

 bad been made before Mayer wrote bis paper in 1842. Mayer 

 discourses to the same effect as Seguin, but at greater length, 

 with greater perspicuity, and with more copiousness of illustra- 

 tion. He adopts the same hypothesis as the latter philosopher, 

 viz. that the heat evolved on compressing an elastic fluid is 

 exactly the equivalent of the compressing force, and thus arrives 

 at the same equivalent, viz. 365 kilogrammes per 1° Cent. 



It must be remarked that, at the time Seguin and Mayer 

 wrote, there were no known facts to warrant the hypothesis they 

 adopted. There was no reason to assert that the heat evolved 

 by compressing a gas was even approximately the equivalent of 

 the compressing force. This being the case may account for the 

 inattention of the scientific world to these writings. The dyna- 

 mical theory of heat certainly was not established by Seguin and 

 Mayer. To do this required experiment ; and I therefore fear- 

 lessly assert my right to the position which has been generally 

 accorded to me by my fellow physicists as having been the first 

 to give a decisive proof of the correctness of this theory. 



In saying this I do not wish to claim any monopoly of merit. 

 Even if Rumford, Mayer, and Seguin had not produced their 

 works, justice would still compel me to share with Thomson, 

 Rankine, Helmholtz, Holtzman, Clausius, and others, whose 

 labours have not only given developments and applications of 

 the dynamical theory which entitle them to merit as well as 

 their predecessors in these inquiries, but who have contributed 

 most essentially in supporting it by new proofs. 



Permit me to remark, in conclusion, that I applied the dyna- 

 mical theory to vital processes in 1843* ; and that in 1 847, in a 

 popular lecture published in the f Manchester Courier/ I ex- 

 plained the phenomena of shooting-stars, and also stated that 

 tbe effect of the earth falling into the sun would be to increase 

 tbe temperature of that luminary f. Since that time Thomson, 



* Phil. Mag. S. 3. vol. xxiii. p. 442. 



f Ibid. vol. xxxii. p. 350; and Manchester Courier, May 12, 1847. 



