for Measuring the Expayisions of Solids, ^c. 195 



Nevertheless, it is a curious fact, that M. Guyton's Essay 

 contains proof that his determination is erroneous, and that 

 mine is a near approximation to the truth. As a collateral 

 means of verifying the indications of instruments intended to 

 measure high degrees of temperature, he refers to the calori- 

 meter as capable of affording the necessary data by a calcula- 

 tion from the amount of heat communicated to known quan- 

 tities of ice or water by bodies in a state of incandescence ; 

 and he quotes the very exact experiments of MM. Clement 

 and Desormes, who had in this manner determined the fol- 

 lowing points : 



By the Liqueiac- By the Heat com- 



tion of Ice. muiucated to Water. 



Fahr. Fahr. 



Temperature of soft iron melted ... 3988° 3902^ 



Castironjust on the point of melting 3164 



Red hot iron 2732 



White hot ditto 3282 



Iron just ceasing to be luminous "> lo-o 



in day-light / ^"^'"^ 



Melted copper 2294- 



My own determinations of the melting point of cast iron, 

 3479^, of that of copper, 254'8-, and of a red heat, about 1000% 

 agree very closely and satisfactorily with these results, with 

 which I was unacquainted at the time of my experiments. 

 M. Guyton's remark upon the latter is : "11 suffit de jeter un 

 coup-d'oeil sur les resultats,'pour recueillir de nouvelles preuves 

 univoques de la necessite de reduire les valeurs donnees par 

 Wedgwood aux degres de son pyrometre. Mais je ne crains 

 pas de dire que ces reductions sont ici portees trop loin, ainsi 

 qu'on pent en juger en les rapprochant de celles auxquelles 

 j'ai ete conduit par I'ensemble des experiences rapportees dans 

 cet essai. Ce n'est pas que je veuille repandre des doutes sur 

 I'exactitude des observations dont je dois la communication 

 aux deux habiles chimistes ci-dessus cites ; mais il est aise de 

 faire voir que la difference des resultats est due, pour la plus 

 grande partie, a la difference des procedes ; de sorte que les 

 evaluations qu'ils ont donnees aux degres de I'echelle de 

 Wedgwood, peuvent, en derniere analyse, et en prenant les 

 termes n)oyens dans la latitude que comportent des operations 

 aussi delicates, servit plutot a confirmer qu'a detruire le sys- 

 teme de correction que j'ai ctabh." 



It is worthy of observation, that had the degrees of Wedg- 

 wood's pyrometer been valued from this determination of the 

 fusing point of iron, the result would have better corresponded 

 with the whole series of pha-nomena. Instead of 130- Fahr. 

 as fixed bv the inventor, or 62°'.5 as corrected bv M. Guyton, 



2 C 2 ■ thcv 



