the spring _2_. Such devices as this are largely used in connection
with so-called "bridging" telephones in which the generators and bells
are adapted to be connected in multiple across the line.

A better arrangement for accomplishing the automatic switching on the
part of the generator is to make no use of the crank shaft as a part
of the conducting path as is the case in both Figs. 74 and 75, but to
make the crank shaft, by its longitudinal movement, impart the
necessary motion to a switch spring which, in turn, is made to engage
or disengage a corresponding contact spring. An arrangement of this
kind that is in common use is shown in Fig. 76. This needs no further
explanation than to say that the crank shaft is provided on its end
with an insulating stud _1_, against which a switching spring _2_
bears. This spring normally rests against another switch spring _3_,
but when the generator crank shaft moves to the right upon the turning
of the crank, the spring _2_ disengages spring _3_ and engages spring
_4_, thus completing the circuit of the generator armature. It is seen
that this operation accomplishes the breaking of one circuit and the
making of another, a function that will be referred to later on in
this work.

[Illustration: Fig. 76. Generator Cut-in Switch]

Pulsating Current. Sometimes it is desirable to have a generator
capable of developing a pulsating current instead of an alternating
current; that is, a current which will consist of impulses all in one
direction rather than of impulses alternating in direction. It is
obvious that this may be accomplished if the circuit of the generator
be broken during each half revolution so that its circuit is completed
only when current is being generated in one direction.