( ?o ) 
' 3 ifcharg*d-upoTi the opening of the Code. After the 
Cock has been Ihut, when no more /'incomes, and 
Water fucceeds, after fome time, Air will extricate it 
Cdf out of the Water and come up to C’C* or if it 
comes from the Parts of the Pipe towards it will 
rife contrary to -the Current of the Water quite up to. 
C, and fo go out at the Pipe EH, when the Cock is 
open’d again. 
As after the firft Difcharge of the Air, it cannot 
be known when more Air is g/)t into the Pipe, unlefs 
by opening the (iock,- which wou d require one Man 
to attend each. Cock conftantly, and occafion a wafle 
oT Water at every turn of the Cock, unlefs when Air 
happens to be in the Pipe ^ it was propos’d to contrive 
a Valve that Ihou’dopen to let out the Air, and Hiut 
again when the Water came ^ and an inverted Brafs 
Clack or Valve fliutting upwards, and falling down 
by its own Weight, with Cork fix’d to the Under-fide 
of it to help it to rife when the Water came, was men- 
tion’d as^fit for the Purpofe by foine of the Perfons 
that I was talking with about it. But we rejected that 
Propofal; becaufe, when fuch a Valve has been fhut 
fome time, if Airlhou’d extricate itfclf from the VVa- 
ter, itwou’d be denfe Air, whofe Force being equal 
to that of a Pillar of Water 3c, 60, 80 or more Feet 
in height, it wou’d keep the Valve fliut as well as the 
Water did before, tho’ the Air at firft cou’d not fliut 
the faid Valve. 
At'lafl:, after feveral Thoughts, we contriv’d a Ma- 
chine which exadly anfwers the Purpofe, and is very 
(imple ^ therefore it will be of general Ufe. 
The Defeription of it is as follows. 
In the fourth Figure G is a Seclion of the Main or 
Conduct Pipe, with Water up to G, and Air above it, 
^ B being an horizontal Linetouc^Tng the Top of the 
faid Pipe; EHli^ the Leaden Pipe deferib’d above, 
and 
