On Mr, JFadgwood* s Vyrometer, 153 



prefent a feries of experiments, according to which he efta- 

 blifhes his theory 5 and he cdncludes with fome obfervations 

 on caloric. '^ It a6ls," fays the author, *' on bodies not 

 equally dilatable, in a manner analogous to folvents, by com- 

 bating the force of cohefibn, arid thereby putting the parts 

 in a ftate to exercife their reciprocal a6lion. Its action con- 

 curs with that of the folvents to oppofe the force of cohefioii ; 

 and hence it happens that the fdlution of a fait by water 

 varies according to the degrefes of temperature. When ca- 

 loric afts on bodies unequally dilatable, it produces fepara- 

 tions and new combinations indeperidently of the affinity 

 peculiar to thefe fubftances, in the fame mahner as folvents 

 when ailing on bodies unequally foluble. 



XIX. On Mr, Wedgwood's 'Pyrometer, 



^y S the conllruftion and ufe of this valuable iriftrument, 

 the only one yet invented which can convey to the mind any 

 accurate ideas refpefting high degrees of heat, and enable us 

 to compare them with each other and with lower degrees, is 

 very generallyv^knowu, a long defcription of it would be fu- 

 perfluous. We fhall therefore briefly obferve, that its indi- 

 cations-are obtained from the property which all clavs pofTefs, 

 of (lirinking or being diminifhed in bulk by expofure to heat ; 

 that, confcquently, any piece fitted into a tapering gauge (for 

 infiance^ a fedor opened a little,) will; after expofure to a 

 fufficient degree of heat, pafs further into the gauge ; and 

 'that, the greater the degree of heat it has expericiiced, the 

 greater will be its diminution of volume, and the deeper will 

 it go into the gauge. Different divifions marked ort the fide 

 \i{ the gauge will, of courfe, give the comparative degrees of 

 heat, to which pieces of the fame clay, fize, and form, may 

 have been expofed. Mr. Wedgwood's gauge confifts of two 

 rulers or flat pieces, a quarter of an inch thick and 24 inches 

 long, fixed upon a fmdoth flat plate, 5-ioths of an inch afun- 

 dcr at one end and 3-ioihs at the other, fo that they include 

 between them a long converging canal or groove; and tlie 

 rule which forn]s one of the fides of this groove is divided 

 Vol. IX. TJ into 



