become full, its neck is played between the jaws of the clamp, _p_.
Upon turning the hand wheel, L, the bottle and the receptacle that
holds it are lifted, and the mouth of the bottle presses against a
rubber disk fixed under the support, C D. The pressure of the neck of
the bottle against this disk is such that the closing is absolutely
hermetical. The support, C D, contains an aperture which allows the
interior of the bottle to communicate with a glass tube, _a b_, which
thus forms a prolongation of the neck of the bottle. This tube is very
narrow and is divided into fiftieths of a cubic centimeter. A
microscope, _m_, fixed in front of the tube, magnifies the divisions,
and allows the position of the level of the water to be ascertained to
within about a millionth of a cubic centimeter.

A force and suction pump, P, sucks in air through the tube, _t_, and
compresses it through the tube, _t'_, in the copper tube, T, which
communicates with the glass tube, _a b_, after passing through the
pressure gauge, M. This pump, then, compresses the air in the bottle,
and the gauge accurately measures its pressure.

To make a test, after the bottle full of water has been fastened under
the support, C D, the cock, _s_, is opened and the liquid with which
the small reservoir, R, has been filled flows through an aperture above
the mouth of the bottle and rises in the tube, _a b_. When its level
reaches the division, O, the cock, _s_, is closed. The bottle and its
prolongation, _a b_, are now exactly full of water without any air
bubbles.

The pump is actuated, and, in measure as the pressure rises, the level
of the liquid in the tube, _a b_, is seen to descend. This descent
measures the expansion or flexion of the bottle as well as the