lling and after the
called station responds--the relay is not so bridged.

[Illustration: Fig. 459. Principle of Western Electric Coin Collector]

The armature of the relay responds only to a high potential and this is
applied by the operator. If the coin is to be taken by the company, one
polarity is sent; if it is to be returned to the patron, the other
polarity is sent. These polarities are applied to a limb of the line
proper. It will be recalled that pressures to actuate service meters are
applied to the test-strand. If wished, keys may be arranged so as to
apply 30 volts to the test-strand and the collecting potential to the
line at the same operation. This enables the service meter to count the
tokens placed in the cash box of the coin collector, and serves as a
valuable check.

In automatic systems, in one arrangement, coin collectors are arranged
so that no impulses can be sent unless a coin has been deposited, the
coin automatically passing to the cash box when the called subscriber
answers, or to the patron if it is not answered. In another arrangement,
calls are made exactly as in unlimited service, but a coin must be
deposited before a conversation can be held. The calling person can hear
the called party speak and may speak himself but can not be heard until
the coin is deposited. No coin-return mechanism is required in this
method.

Coin collectors of these types usually are adapted to receive only one
kind of coin, these, in the United States, being either nickels or
dimes. For long-distance service, where the charges vary, it is
necessary to signal to an operator just what coins are paid. It is
uniformly customary to send these signals by sound, the collector being
so arranged that the coins strike gongs. In coin collectors of the Gray
Telephone Paystation Company, the coins strike these gongs by their own
weight in falling through chutes. In coin collectors of the Baird
Electric Company, the power for the signals is provided by hand power, a
lever being pulled for each coin deposited. Both methods are in wide
use.

CHAPTER XXXIX

PHANTOM, SIMPLEX, AND COMPOSITE CIRCUITS

=Definitions.= Phantom circuits are arrangements of telephone wires
whereby more working, non-interfering telephone lines exist than there
are sets of actual wires. When four wires are arranged to provide three
metallic circuits for telephone purposes, two of the lines are physical
circuits and one is a phantom circuit