e
terminals are indicated by the numerals _1_ and _2_, _3_ being a dry
wooden block arranged between the terminals at one end for securing
greater rigidity between them.

[Illustration: Fig. 316. Line Lamp Mounting]

The method of mounting these lamps is subject to a good deal of
variation in detail, but the arrangement is always such that the lamp is
slid in between two metallic contacts forming terminals of the circuit
in which the lamp is to operate. Such an arrangement of springs and the
co-operating mounting forming a sort of socket for the reception of
switchboard lamps is referred to as a _lamp jack_. These are sometimes
individually mounted and sometimes mounted in strips in much the same
way that jacks are mounted in strips. A strip of lamp jacks as
manufactured by the Kellogg Company is shown in Fig. 316. The
opalescent lens is adapted to be fitted in front of the lamp after it
has been inserted into the jack. Fig. 317 gives an excellent view of an
individually-mounted lamp jack with its lamp and lens, this also being
of Kellogg manufacture. This figure shows a section of the plug shelf
which is bored to receive a lamp. In order to protect the lamps and
lenses from breakage, due to the striking of the plugs against them, a
metal shield is placed over the lens, as shown in this figure, this
being so cut away as to allow sufficient openings for the light to shine
through. Sometimes instead of employing lenses in front of the lamps, a
flat piece of translucent material is used to cover the openings of the
lamp, this being protected by suitable perforated strips of metal. A
strip of lamp jacks employing this feature is shown in Fig. 318, this
being of Dean manufacture. An advantage of this for certain types of
work is that the flat translucent plate in front of the lamp may readily
carry designating marks, such as the number of the line or something to
indicate the character of the line, which marks may be readily changed
as required.

[Illustration: Fig. 317. Supervisory Lamp Mounting]

[Illustration: Fig. 318. Line Lamp Mounting]

[Illustration: Fig. 319. Individual Lamp Jacks]

In the types made by some manufacturers the only difference between the
pilot lamp and the line lamp is in the size of the lens in front of it,
the jack and the lamp itself being the same for each, while others use a
larger lamp for the pilot. In Fig. 319 are shown two individual lamp
jacks, the one at the top being for supervisor