and Apparatus for producing Water. $7 
begins at R. When the index is in a vertical pofition, the 
cock is completely open. 
_ As it might perhaps be difficult to give to the cock P, 
which is connected with a ciftern of water, fuch an opening 
as not to permit more water to flow through it than necef- 
fary for preferying a height of four inches in the cylinder O, 
a wafte pipe TT is applied at this height, which fuffers all 
the fuperfluous water of the cock P to run off. In order 
that it may be more conveniently obferved, whether the cock 
P has a fufficient opening for maintaining a four-inch. co- 
Jumn of water, a glafstube U, marked at the required height, 
is applied on the outfide, connected with the cylinder O. 
To fill this gazometer, nothing more is neceffary than to 
let water run out from the cylinder H. For this purpofe, 
the cock V muft be opened. until the water in H fiands 
Jower than that in-A. The cock D, and the cock W, ftand- 
ing over the bell X, are then opened. The air contained in 
X rifes through the plable tube YY into A. This filling 
may be continued, by leaving the cock V open, that the 
water which proceeds through the fyphon from A to H may 
run out, and the furface of the water in H ftand always a 
few inches lower than that in A. At the fame time the 
bell X is to be fupplied with new’ gas in the ufual manner, 
When the operation of filling is completed, the cock V is 
to be fhut, and that at Z opened ; the lower part of the open- 
ing of the key of which is in the fame horizontal line with 
zero of the feale, which fhews in cubic inches the altitude 
of the water in A. By thefe means the water falls no lower 
in A than to the above-mentioned line; and A is confe- 
quently filled with air to the beginning of the feale a4. Be- 
fore the cock D is fhut, care muft be taken that the water in 
the bell X do not ftand higher than the water that furrounds 
it in its tub, which may be effected, if the bell be de- 
preffed in the tub till the internal and external altitude of 
the water be perfectly equal; and the air in A will then be 
of the fame denfity as that of the atmofphere, 
! G 4 The 
