[ 6 92 ] 
As all chemical Digeftions, where an equable 
Heat is to be continued for fome time together, will 
come in between hot Simfhine and the boiling of 
Quickftlver, a Thermofcope of that Range will be 
fufficient for common Ufes; and therefore one fit- 
ted with a brafs Rod will anfwer thefe Purpofcs. 
In large Furnaces for running down Ores, or 
melting great Quantities of Metal together, it is not 
poilible to place fuch an Inftrument 5 but then in 
Lead and Tin there may be fmall Outlets contrived, 
into which fome of the melted Metal may be permit- 
ted to flow, and remain in Conrad with the fame Body 
of Metal within, where the Inftrument may be placed ; 
and for placing a Thermofcope in Iron, Copper, or 
Glafs Furnaces, there maybe aPlace contrived, which 
lhall not open into the Furnace, but have the Thicknefs 
of a Stone or Brick left between, upon which the In- 
ftrument may be plac'd 5 and tho’ in fuch a Situation 
it will not meal ure the a&ual Heat within the Fur- 
nace, it will always give the relative or comparative 
Heat in the like Circumftances at different Times, 
and fo fhew us how to regulate the Heat within. 
Altho' a Chemift: lhall have one of thefe Inftru- 
ments to meafure the Heat, he lhall have ufed in 
any Experiment, and have noted down the feveral 
Degrees made ufe of, and the Time each lafted, he 
ftill labours under another Difficulty, which is the 
not being able to command any required Heat, and 
that it lhall laft: a certain required Time, unlefs it 
be below that of boiling Water, which may be pro- 
cured and continued by various Contrivances of 
Lamps, either of Spirits, or of Oil 5 but how to con- 
tinue a Fire for 12 or 24 Hours together, without At- 
tendance, which lhall continually keep Quickfilver 
boiling, 
