may be left operatively connected with the line while the instrument
is not being used in the transmission of speech, and in order that the
signaling apparatus may be cut out when the talking apparatus is
brought into play.

In instruments employing batteries for the supply of transmitter
current, another switching function is the closing of the battery
circuit through the transmitter and the induction coil when the
instrument is in use for talking, since to leave the battery circuit
closed all the time would be an obvious waste of battery energy.

In the early forms of telephones these switching operations were
performed by a manually operated switch, the position of which the
user was obliged to change before and after each use of the telephone.
The objection to this was not so much in the manual labor imposed on
the user as in the tax on his memory. It was found to be practically a
necessity to make this switching function automatic, principally
because of the liability of the user to forget to move the switch to
the proper position after using the telephone, resulting not only in
the rapid waste of the battery elements but also in the inoperative
condition of the signal-receiving bell. The solution of this problem,
a vexing one at first, was found in the so-called automatic hook
switch or switch hook, by which the circuits of the instrument were
made automatically to assume their proper conditions by the mere act,
on the part of the user, of removing the receiver from, or placing it
upon, a conveniently arranged hook or fork projecting from the side of
the telephone casing.

Automatic Operation. It may be taken as a fundamental principle in
the design of any piece of telephone apparatus that is to be generally