196 . A Superwor Green Dye. 
measuring the compression of water. After having depriv- 
ed the water of atmospheric air by ebullition, l 
glass cylinder with it, whose upper part is mounted with a 
brass cover, hermetically sealed, a ich is traversed by 
a screw, with a small brass piston at its lower extremity 
which presses upon the fluid. In the cylinder is placed a 
ball with a small thermometer tube, both filled with the wa- 
ter of the cylinder, except that in the upper part of the 
tube, which remains open, there is a small column of mer- 
cury, which on account of the extreme fineness of the tube, 
keeps its place without falling into the ball. 
Now suppose that the water is compressed by turning the 
screw of the piston ; this pressure being equal both within and 
without the ball and its tube, they will undergo neither expan- 
sion nor contraction, and consequently the position of the 
mercury above the water in the thermometric tube will im- 
in the cylinder. He has ascertained by this instrument 
that the compressibility of water diminishes very rapidly 
as the pressure increases, and that the mean compressibili- 
ty under a pressure of three or four atmospheres is z57¢s03, 
for each atmosphere, a result which very nearly accords 
with the experiments of Canton. 
