illuminating gas in our homes and offices. The gauge is attached to
the gas burner and the pressure is read by means of a scale attached
to the gauge. (See Laboratory Manual.)

In order to have satisfactory illumination, the pressure must be
strong enough to give a steady, broad flame. If the flame from any gas
jet is flickering and weak, it is usually an indication of
insufficient pressure and the gas company should investigate
conditions and see to it that the consumer receives his proper value.

87. The Gas Meter. Most householders are deeply interested in the
actual amount of gas which they consume (gas is charged for according
to the number of cubic feet used), and therefore they should be able
to read the gas meter which indicates their consumption of gas. Such
gas meters are furnished by the companies, and can be read easily.

[Illustration: FIG. 53.--The gas meter indicates the number of cubic
feet of gas consumed.]

The instrument itself is somewhat complex. It will suffice to say that
within the meter box are thin disks which are moved by the stream of
gas that passes them. This movement of the disks is recorded by
clockwork devices on a dial face. In this way, the number of cubic
feet of gas which pass through the meter is automatically registered.

89. The Relation between Pressure and Volume. It was long known that
as the pressure of a gas increases, that is, as it becomes compressed,
its volume decreases, but Robert Boyle was the first to determine the
exact relation between the volume and the pressure of a gas. He did
this in a very simple manner.