[ 6 °2 ] 
For this purpofe, let there be prepar’d a bar of 
ftrait-grain d white deal, or cedar ; which, it is well 
known, are much lefs expanfible by heat than any 
metal hitherto difcover’d : Let the bar be adapted to 
the inftrument in like manner as the other bars in- 
tended to be meafur’d ; but that the foftnefs of the 
wood may not hinder the juftnefs of its bearings, let 
its ends be guarded with a bit of brafs let into the 
wood at the points of contadt, to prevent, as much 
as may be, the moifture or fteam of the water from 
affedting the wood ; let it firft be well varnifli’d, and 
then, being wrapp’d round with coarfe flax from end 
to end ; this will, in a great meafure, imbibe the va- 
pour, before it arrives at the wood. Let the ciftern 
alfo be fo contriv’d, that the inftrument being fup- 
ported at a proper height therein, the bar to be mca- 
fur’d may, upon occafion, be above the cover, while 
the bafis remains in the water : Thus will the cover 
alfo be a defence againft the moifture. Let the water 
in the ciftern be now brought to its lower degree of 
heat (fuppofe at or near the freezing point), the bafis 
having continu’d long enough in the water to re- 
ceive the fame degree of heat, and the wooden bar 
having been previoufly kept in an adjacent room, not 
fubjedt to fudden alterations of temperature by fire, 
or other caufes ; let the bar be apply’d to the in- 
ftrument, and the degrees of the micrometer and the 
thermometer read off, and fet down : Let the wooden 
bar be then reftor’d to its former place, till the water 
is heated to the greater degree intended (fuppofe at or 
near that of boiling water) ; the lid being now fhut 
down, and the chinks flopp’d with coarfe flax, to pre- 
vent the iffuing of the fteam as much as poflible, let 
the 
