regijlers the Temperature. 267 



AB is filled with the firongeft fpirit of wine or alcohol, and from B to E is filled with 

 mercury. 



It will be evident from infpection, that if the fpirit of wine is expanded by heat, the mer- 

 cury in the fmaller tube will rife ; and if the fpirit of wine is contradted by cold, the mercury 

 will fall ; and although they are both fubjeded to the preflure of the atmofphere, yet as liquids 

 are incompreflible by weight in any perceptible degree, neither the fpirit of wine nor mercury 

 will be altered in bulk by the different weights of the atmofphere. 



F D is a fcaleof brafs or ivory about fix and a half inches long, divided in the ufual way. 



E is a fmall conical piece of ivory or glafs of a proper weight, made to float on the fur- 

 face of the mercury in the fmaller tube ; to which float is joined a wire reaching to H 

 having a knee bent at a right angle, which raifes one index, and deprefTes another index, 

 according as the mercury rifes or falls, which wire fhall be termed Refloat wire. 



I I is a glafs tube feven inches and a half long, clofed at top, and open at bottom, fo 

 wide as to Aide eafily over the fcale ; and by means of a brafs rim cemented to it is made to 

 fit exadlly to the circular bafe of the fcale, fo that when this tube is put on, it covers the 

 whole fcale, and hinders and defends them from wind or rain. This cover need not be taken 

 off, except when the inftrument is to be prepared for an obfervation. 



The operation of the float and indexes will be better underftood from fig. 2, which re- 

 prefents them of the full fize. 



F G is the fcale fixed to a circular piece of wood or brafs through which the top of the 

 fmall tube is made to pafs. 



From G to K is a piece of the fmalleft harpfichord wire, or rather of the fmalleft gold 

 wire, ftretched along the fcale, fixed at the ends by two brafs pins. 



L, L, are two indexes formed of thin black oiled filk, pierced by the fmall wire in fuch a 

 manner as to Aide upwards and downwards with a very fmall force, not more than two grains. 



H, the knee of the float wire, before defcribed, is made to encompafs the fmall wire between 

 the two indexes, fo that when the float rifes, the upper index is moved upwards, and when 

 it defcends, it leaves the upper index ftationary, and pufhes down the lower index, which is 

 alfo left ftationary when the float rifes. 



When the inftrument is to be prepared for an obfervation, the one index is to be pulled 

 down, and the other raifed, by means of a bit of wire bent for the purpofe, until both indexes 

 touch the knee of the float wire ; and when it is again obferved, the upper index will point 

 out the greateft degree of heat, and the lower the greateft degree of cold. 



If this thermometer is to be adapted to a piece of clock-work in order to record the degrees 

 of heat at each hour and minute of time, it ought to be made of larger dimenfions. The 

 large tube may be forty inches long, and not increafed in diameter, but the fmall tube ought 

 to be enlarged in diameter, and not in length. By enlarging the tube which contains the 

 fpirit of wine in length only, it will be affefted by heat and cold in as fhort a time as that 

 before defcribed. 



It is unneceffary at prefent to explain the clock-work. It is fufficient to fay, that a hollow 



cylinder. 



