the \ Thermometer for high Degrees of Heat . ^395 
rods are prefled, and on which their figure and dimenfions de- 
pend, as to fuperfede the ufe of the paring gage altogether ; 
that'the whole furface may remain of the lame uniform com- 
pact nefs which it received in the prefs. And as it is fcarceiy 
practicable, in any mode of forming foft clay, to have all the 
pieces precifely of the fame dimenfions after drying, I do not 
rejeCt thofe which come within two or three degrees of the 
ftandard, but, infteadof injuring the furface by paring or rub- 
bing, I mark on the ends the degrees which they refpeCtively 
exceed or fall fhort ; which degrees are accordingly to be fub- 
ftraCted, or added, in all obfervations of heat made with thofe 
pieces. StriCtly fpeaking, an allowance ought to be made alfo 
for the proportional diminution upon this excefs or deficiency 
itfelf ; but the allowance for three degrees would not, at the 
melting heats of copper, filver, or gold, amount to more than 
a feventh part of a degree; and at the extreme point of heat 
that I have been able to attain, when the piece has diminilhed 
iLfJL, or nearly one-fourth of its whole thicknefs, it comes 
only to four-fifths of a degree. 
It may be proper to take notice of an irregularity in the 
apparent diminutions of the pieces, which was fometimes ob~ 
ferved to happen from another caufe, their bending a little in 
ftrong fire, fo as to be prevented from going fo far in the gage 
as they would have done if they had continued perfectly 
ftraight. But as this takes place only in pieces of confiderable 
length, and as they derive no advantage of any kind from that 
length, the remedy is too obvious to need being here men- 
tioned. 
Another fallacious appearance arofe, not from any imper- 
fection in the pieces themfelves, but from a deception with 
refpeCt to the heat in which the comparifon of them had been 
Vol. LXXVI. Fff made. 
