FOR MEASURING THE EXPANSION OF SOLIDS. 
261 
incandescence ; and he quotes the very exact experiments of MM. Clement 
and Desormes, who had in this manner determined the following points : 
By the Liquefaction By the Heat commu- 
of Ice. nicated to Water. 
Fahr. Fahr. 
Temperature of soft iron melted ..... 3988° . . 3902° 
Cast iron just on the point of melting . . . 3164° . . 
Red hot iron 2732° . . 
White hot ditto 3282° . . 
Iron just ceasing to be luminous in day- light . . . 1272° 
Melted copper . . 2294° 
My own determinations of the melting point of cast iron, 3479°, of that of 
copper, 2548°, and of a red heat, about 1000°, agree, very closely and satisfac- 
torily with these results, with which I was unacquainted at the time of my ex- 
periments. M. Guyton’s remark upon the latter is : “ II suffit de jeter un coup- 
d’oeil sur les resultats, pour recueillir de nouvelles preuves univoques de la ne- 
cessite de reduire les valeurs donnees par Wedgwood aux degr6s de son pyro- 
metre. Mais je ne crains pas de dire que ces reductions sont ici portees trop 
loin, ainsi qu’on peut en juger en les rapprochant de celles auxquelles j’ai ete 
conduit par l’ensemble des experiences rapportees dans cet essai. Ce n’est pas 
que je veuille repandre des doutes sur l’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 precedes ; de sorte que les evaluations qu’ils ont donnees 
aux degr^s de l’echelle de Wedgwood, peuvent, en derniere analyse, et en pre- 
nant les termes moyens dans la latitude que comportent des operations aussi 
delicates, servir plutot a confirmer qua detruire le systeme de correction que 
j’ai etabli.” 
It is worthy of observation, that had the degrees of Wedgwood’s pyrometer 
been valued from this determination of the fusing point of iron, the result would 
have better corresponded with the whole series of phenomena. Instead of 130° 
Fahr. as fixed by the inventor, or 62°.5 as corrected by M. Guyton, they would 
have been estimated at about 20° Fahr. ; and taking Mr. Wedgwood’s original 
determination of the fusing point of silver at 28° of his scale and the zero point 
at 1077°, the former would come out about 1650°. By raising the zero point 
a little, (and it is much more probable that the temperature of a red heat fully 
