96 Mr. Patten’s Air Pump, Gazometer, &c. 
der E, the water in the cylinder F is expelled between the 
two outer cylinders at the aperture L; and its place sup- 
plied through the valve G, by the gas that was in the cyl- 
inder E; now if the cylinder is again filled with gas through 
D, both it and ihe cylinder F are full and may be used 
gra 
the weights can only be equivalents when the index is at 
rest, which may be any where within the quantity required 
to turn the beam-—sufficiently accurate for all common pur- 
