360 Mr, Wspewoon’s Method of conneéting °° 
avhence either, fcale is eafily reducible to,the other through 
their whole range, whether we fuppofe FAHRENHEIT’s contix | 
nued upwards, or mine downwards. | mt 3 
_ For obtaming the intermediate thermometer different means 
were thought of ; but the only principle which, upon attentive 
confideration, afforded any profpect of fuccefs, was the expan- 
fion of metals. ‘Uhis therefore was adopted, and among dif- 
ferent methods of meafuring that expanfion, which either oc- 
curred to myfelf, or which I can find to have been praétifed by 
others, there is no one which promifes either fo great accuracy, 
or convenience in ufe, as a gage like that by which the ther- 
‘mometer pieces are meafured: the utility of this gage had now 
been confirmed to me by experience, and the machines and 
long rods, which have been employed for meafuring expanfions 
on other occafions, were abfolutely inadmiffible here, on ac- 
count of the infuperable difficulties of performing nice opera- 
tions of this kind in a red heat, and of communicating a per- 
fectly equal heat through any confiderable extent. | 
To give a clearer idea of this fpecies of gage, which, fas 
ple as it is, I am informed has been mifunderftood by fome of 
the readers of my former paper, a reprefentation of one ufed 
on the prefent occafion is annexed in fig. 4. where ABCD is a 
{mooth: flat plate; and EF and GH two rulers or flat pieces, a 
quarter of an inch thick, fixed flat upon the plate, with the 
fides that are towards one another made perfeétly true, a little: 
further afunder at one end EG than at the other end FH; thus” 
they include between them a long converging canal, which : 
divided on one fide into.a number of {mall equal parts, an 
which may be confidered as performing the offices both of ud 
tube and fcale of the common thermometer. It is obvious, 
that if a body, fo adjufted as to fit exactly at the wider end of 
this 
: 

} 
