On Mr. IVedgWDod's Pyrometer* 1^7 



ccflTary to fufc the different metals, &;c, 8cc. and note them 

 by the refults obtained from the pyrometers made from known 

 .materials \ noting, at the fame time, how ;n any degrees of 

 the mercurial thermometer correfpond to one on Wedg- 

 wood's fcale. Or, 



2. The obje6t in view might perhaps be more eafily at- 

 tained by accommodating the width of the two pieces of brafs 

 in VVedgwood's fcale to tlie flirinkage of the new pyrometers, 

 in fuch a manner, that at the wide end, or zero, they might 

 remain a« at prefcnt, and, by making them approach to or 

 recede from each other at the other end, receive the new 

 pieces at that part of the gauge which (hall indicate the proper 

 degree, obt-ained by comparing the refuks of fome experi- 

 ments made with them and fomq of Mr, Wedgwood's old 

 cylinders, which, though fcarce, may Hill be had. 



We fliall make ourfelves, perhaps, better underftood by 

 alTuming fuppofed refults to fliow the kind of alteration that 

 would be neceflary to accommodate the indications of the 

 new pyrometers which we propofe, to thofe which have been 

 -determined by Mr. Wedgwood^s. 



Expofe one of each to a ftrong heat in a clofe crucible. 

 When withdrawn, fay Mr. Wedgwood's indicates ioo% and 

 that the other wguld reach lio°. In this cafe the new py- 

 rometer would havp (larui^k niore in the fame degree of heat 

 than the old one; and to make it (land at loo^, the true de- 

 gree by Wedgwood's fcale, (which we think ought by no 

 means ^o be altered,) all that would he neceflary would be 

 to bring the lides of the gauge fo much nearer to each other 

 ^t the narrow end pf the groove as to make the new pyro- 

 yneter piece Hop at the proper degree. If thefe two pieces 

 were aoain expofed, together, to a ftronger degree of heat, it 

 would be found, that whatever degree Mr. Wedgwood's 

 might indicate in a gauge that had not been altered, the new 

 pyrometer would alfo indicate \w the one that had beeu 

 accommodated to it after the former expofure to heat. 



If the n^vy pieces wpre found to fliri^k lefs than the old 



ones, the gauge, of coyirfc, would require to be proportionally 



widened at the narrow end, to allow it to reach the degree 



indicated by Mr. Wedgwood's pyrometer ; and in either cafe, 



4 ^M 



