E- goo J 
_ Air extracted from fpars cannot 
be examined, nor even obtained, 
but by making ufe of mercury 
inftead of water: for this fingular 
air, which corrodes glafs, 1s im- 
mediately reduced into itone by 
the firft contact with water. 
This trough confifts of two dif- 
ferent ftrong wooden boxes. a a 
§ 
is the box containing the mercur 
it is in the infide 1lf~ ras eiches | 
long, 4. inches and 2 lines deep, 
and 4 inches and 2 lines wide. 
The board ¢ is placed at one inch 
and 2 lines diftance from the brim, 
and is 7 lines thick. The orifice d of 
the funnel hollowed out of the un- | 
der-fide of this board is two lines ‘ 
above the furface of the board. — 
This box is placed within another _ 
larger box epally. ftrong, 4d by 
which — 
EN Ses, eT BE oe BS ee a ae ME ea ae ae ee oe ee Ce 
