A standard of illuminating power. It is the light emitted by a
three-inch Argand gas flame through a rectangular aperture in a silver
plate carried by a screen. The aperture is of such size and so far
distant from the flame as to permit the passage of exactly two candles
illuminating power.

A combined current and potential meter. It is constructed on the general
lines of a Siemens’ Electro Dynamometer. If in it one coil is made of
coarse wire and is placed in series with the current conductor, and if
the other is wound with fine wire and is connected as a shunt from point
to point whose potential difference [...]

An electric meter which measures the length of time during which current
is used. It assumes a constant current and potential. It is virtually a
clock, which is turned on when the current passes, and is turned off
with the current.

A current meter in which the current is measured by the heat it imparts
to a conductor. In one meter a very light helix of mica is poised
horizontally over a conductor, and the whole is enclosed in a case. As
the wire is heated it causes an ascending current of air which rotates
the vane, and the latter [...]

A current meter in which the current is measured by its electro-magnetic
effects.

An instrument for measuring the quantity of electricity in current form
supplied to consumers. It may be of various types. The general principle
involved is that in commercial installations for incandescent light and
power supply a fixed potential is usually maintained, the multiple arc
system being employed. Hence all that is requisite is to measure the
coulombs or the ampere-hours [...]

A current meter in which the current is determined by the amount of
chemical decomposition which it can effect. In the Edison meter the
solution is one of zinc sulphate. Two electrodes of zinc are immersed in
it, and a fractional part of the current is passed through it. The gain
in weight of one electrode and the loss [...]

A unit of illuminating power; the light given by one standard candle at
a distance of one meter. The ordinary units of illuminating power are
altogether relative; this one is definite.

A form of Wheatstone’s bridge in which one lateral pair of arms is
represented by a straight wire. The other pair comprise a known
resistance, and the resistance to be determined. The galvanometer is
connected on one side between the known and unknown resistance. On the
other side its connection is moved back and forth along the straight
wire until [...]

A meter for measuring alternating current, as supplied to consumers,
from an alternating current system. Like most commercial meters its only
function is the measurement of quantity; the potential difference is
maintained at a constant figure by the generating plant.
The cut shows the Schallenberg meter. It is simply an alternating
current motor (see Motor, Alternating Current), with air vanes [...]