hrough the two
right-hand normally closed contacts of the switch on the generator.
When, however, the generator is operated these two contacts are made
to disengage each other while the long spring of the generator switch
engages the left-hand spring and thus brings the generator itself into
the circuit.

[Illustration: Fig. 149. Circuit of Bridging Magneto Set]

Of the three binding posts, _1_, _2_, and _3_, at the top of Fig. 149,
_1_ and _2_ are for connecting with the line wires, while _8_ is for a
ground connection, acting in conjunction with the lightning arrester
mounted at the top of the telephone and indicated at _4_ in Fig. 149.
This has no function in talking or ringing, and will be referred to
more fully in Chapter XIX. Suffice it to say at this point that these
arresters usually consist of two conducting bodies, one connected
permanently to each of the line binding posts, and a third conducting
body connected to the ground binding post. These three conducting
bodies are in close proximity but carefully insulated from each other;
the idea being that when the line wires are struck by lightning or
subjected otherwise to a dangerous potential, the charge on the line
will jump across the space between the conducting bodies and pass
harmlessly to ground.

NOTE. The student should practice making simplified diagrams from
actual wiring diagrams. The difference between the two is that
one is laid out for ease in understanding it, while the other is
laid out to show the actual course of the wires as installed.

If the large detailed circuit of Fig. 149 be compared with the small
theoretical circuit in the same figure, the various conducting
paths will be found to be the same. Such a simplified circuit does
more to enable one to grasp the fundamental scheme of a complex
circuit than much description, since it shows at a glance the general
arrangement. The more detailed circuits are, however, necessary to
show the actual paths followed by the wiring.

The circuits of desk stands do not differ from those of wall sets in
any material degree, except as may be necessitated by the fact that
the various parts of the telephone set are not all mounted in the same
cabinet or on the same standard. To provide for the necessary relative
movement between the desk stand and the other portions of the set,
flexible conductors are run from the desk stand itself to the
stationary portions of the equipment, such