then in
any sensible degree, by any weight it is capable of supporting.

Fig. 6. The trivet, or three branched stirrup, by which the jar A is
hung to the balance, with the screw by which it is fixed in an
accurately vertical position.

Fig. 3. The iron rod 26, 27, which is fixed perpendicular to the center
of the beam, with its box 28.

Fig. 7. & 8. The friction-wheels, with the plates of rock-cristal Z, as
points of contact by which the friction of the axis of the lever of the
balance is avoided.

Fig. 4. The piece of metal which supports the axis of the
friction-wheels.

Fig. 9. The middle of the lever or beam, with the axis upon which it
moves.

Fig. 10. The thermometer for determining the temperature of the air or
gas contained in the jar.

When this gazometer is to be used, the cistern or external vessel, LMNO,
Pl. VIII. Fig. 1. is to be filled with water to a determinate height,
which should be the same in all experiments. The level of the water
should be taken when the beam of the balance stands horizontal; this
level, when the jar is at the bottom of the cistern, is increased by all
the water which it displaces, and is diminished in proportion as the jar
rises to its highest elevation. We next endeavour, by repeated trials,
to discover at what elevation the box 28 must be fixed, to render the
pressure equal in all situations of the beam. I should have said nearly,
because this correction is not absolutely rigorous; and differences of a
quarter, or even of half a line, are not of any consequence. This height
of the box 28 is not the same for every degree of pressure, but varies
according as this is of one, two, three, or more inches. All these
should be registered with great order and precision.

We next take a bottle which holds eight or ten pints, the capacity of
which is very accurately determined by weighing the water it is capable
of containing. This bottle is turned bottom upwards, full of water, in
the cistern of the pneumato chemical apparatus GHIK, Fig. 1. and is set
on its mouth upon the shelf of the apparatus, instead of the glass jar
V, having the extremity 11 of the tube 7, 8, 9, 10, 11, inserted into
its mouth. The machine is fixed at zero of pressure, and the degree
marked by the index 30 upon the sector m l is accurately observed;
then, by opening the stop-cock 8, and pressing a little upon the jar A,
as much air is forced into the bottle as fills it entirely. The degree
marked by the i