Idle Poles.
Poles of wire sealed into Crookes' tubes, not used for the discharge
connections, but for experimental connections to test the effect of
different excitation on the discharge.
Idle Wire.
In a dynamo the wire which plays no part in generating electro-motive
force. In a Gramme ring the wire on the inside of the ring is idle wire.
Igniter.
In arc lamps with fixed parallel carbons of the Jablochkoff type (see
Candle, Jablochkoff) a strip of carbon connects the ends of the carbons
in the unused candle. This is necessary to start the current. Such strip
is called an igniter. It burns away in a very short time when an arc
forms producing the light, and lasts, if all goes well, until the candle
burns down to its end. Without the igniter the current would not start
and no arc would form.
I. H. P.
Symbol for indicated horse-power.
Illuminating Power.
The relative light given by any source compared with a standard light,
and stated in terms of the same, as a burner giving an illuminating
power of sixteen candles. For standards see Candle, Carcel--Methven
Standard--Pentane Standard.
Illuminating Power, Spherical.
The illuminating power of a lamp or source of light may vary in
different directions, as in the case of a gas burner or incandescent
lamp. The average illuminating power determined by photometric test or
by calculation in all directions from the source of light is called the
spherical illuminating power, or if stated in candles is called the
spherical candle power.
Illumination, Unit of.
An absolute standard of light received by a surface. Preece proposed as
such the light received from a standard candle (see Candle, Standard) at
a distance of 12.7 inches. The object of selecting this distance was to
make it equal to the Carcel Standard (see Carcel), which is the light
given by a Carcel lamp at a distance of one meter.
From one-tenth to one-fiftieth this degree of illumination was found in
gas-lighted streets by Preece, depending on the proximity of the gas
lamps.
Image, Electric.
An electrified point or system of points on one side of a surface which
would produce on the other side of that surface the same electrical
action which the actual electrification of that surface really does
produce. (Maxwell.)
The method of investigating the distribution of electricity by electric
images is due to Sir William Thomson. The conception is purely a
theoretical one, and is of mathematical value and interest.