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bar G, which returns all the bars on their con- 
tradion. 
On the dial-plate I, there are three circles defcribecL 
The inward circle is divided into 240°, according to 
Fahrenheit’s fcale. The middle circle is divided into 
360°, which is intended to mark the expanfion of 
different metals. The outward circle is divided into 
2080 parts, to which the longer index / points, which 
marks 18 divifions for each degree of the inward circle ; 
and 1 2 for each degree of the middle circle, pointed to 
by the index k. 
The quarter divifions of the dial are marked I, II, 
III, II 1 I, to fhew, by the index k, how often the 
index / has gone round. 
There is a fcrew-hole towards the point, in the 
index /&, to fix a fmall pencil in ; which is moved by 
the index on a circle of wood, or ivory, and maiks. 
the higheft and lowed: degrees it has pointed to, for 
any time j which laves the continual examination le- 
quifite to form obfervations of this kind ; and the 
mark of the pencil is eaiily rubbed out, when any 
new obfervation is intended. 
The firft bar A of this inftrument may readily be 
taken out, and replaced ; or any other bar of equal* 
length and thicknefs applied ; by which means, the 
inflrument may be ufed as a pyrometer, to mealure 
the expanfion of any bar 1 feet long,, with great 
exadnefs, to the 73,840th part of an inch per foot j 
and, as a thermometer, it marks the alterations in 
the temperature of the air, much more fenfibly than 
any other inflrument for the purpofej the lange of 
the minute index / being 74 inches, by the common 
degrees of heat and cold of this climate. 
If 
