[ 68 9 ] 
has boiled for a Quarter of an Hour, I turn the In- 
dex AB in Fig,. 3. till it (lands in the horizontal 
Pofition, as at B , being the Point of boiling-hot 
Water, and which anfwers to Divifion 212 on Fah- 
renheit's Arch. I then take it out of the Water, 
and dry it, by holding it a little over the Fire: And 
now great Care muft be taken, that nothing alters 
the Situation of the Index upon the Axis; even a 
Nut to fcrew on upon the Axis at C may be the 
beft to keep it fixed. If the Inftrument be left to 
cool in the Air, the Index will fail below B> (hewing 
the Degrees of Cold, or lefs Heat than boiling Wa- 
ter 3 and if put into melting Tin, Lead, <&c, it will 
(hew the Degrees of Heat above boiling Water. A 
brafs Rod will ferve for an Inftrument to meafure; 
the greateft Degrees of Cold, and all the Degrees of 
Heat, to the melting of Silver or Gold ; but if you 
have a Mind to make one to meafure greater De- 
grees of Heat, the Rod muft be of Steel, or the nneft 
Iron. A Rod of Brafs, according to Dr. Mufchen - 
hroek’s Experiments, /. c. was found to lengthen 
377, when one of Iron lengthen'd only 230 Parts. 
An iron Rod, being regulated by boiling W ater, as 
above direded, will meafure not only the Heat of 
melted Tin and Lead, but of Silver, Gold, and Cop - 
per, and will even (hew the Degree when Iron itfeif 
begins to melt, which will be the greateft Degree 
of Elongation of the Rod juft before the Bottom of 
it runs ; and I imagine, that an Inftrument may be 
conftruded with Supporters, and a Rod made of 
Tobacco-pipe Clay, which, being regulated by boil- 
ing Mercury (for it muft never touch Water), may 
Uuuu 2 be 
r 
