| ass 3 
A glafs tube longer than that 
which I had at hand would. bear 
aolarger fcale, and thus indicate 
with {till more accuracy the good- 
nefs of the air: but the two mea- 
fures of air let up muft not fill 
more than one half of the glafs 
tube, for otherwife it could not be 
{hook in the water without danger 
of fome bubbles of air coming out — 
of it, or rufhing in it, by the force: 
Ree eT = a 
In the works of the Rev. Dr. 
Prieftley, one meafure of common 
air is faid to occupy fometimes 120, 
_and even more fubdivifions, which 
is owing to his peculiar method. 
He firft joins the two airs together 
in a feparate jar, and allows them 
to ftand a certain time to incorpo+ 
rate one with the other; after. 
“which, he lets them up in his large . 
sae tube 
