yed--Types--Operator's Transmitter Supply--Ringing-Current
Supply--Auxiliary Signaling Current--Primary Sources--Duplicate
Apparatus--Storage Batteries--Power
Switchboards--Circuits--Central-Office Building--Arrangement of
Apparatus--Manual Offices--Automatic Offices

SPECIAL SERVICE FEATURES _By K. B. Miller and S. G. McMeen_ Page 271

Private-Branch Exchanges--Switchboards--Supervision--With Automatic
Offices--Battery Supply--Ringing Current--Inter-Communicating
Systems--Magneto System--Common-Battery Systems--Types--Long-Distance
Switching--Operator's Orders--Trunking--Way Stations--Traffic--Measured
Service--Charging--Rates--Toll Service--Local Service

TELEGRAPH AND RAILWAY WORK _By K. B. Miller and S. G. McMeen_ Page 321

Phantom, Simplex, and Composite Circuits--Ringing--Railway
Composite--Telephone Train Dispatching--Railroad
Conditions--Transmitting Orders--Apparatus--Telephone Equipment--Types
of Circuits--Test Boards--Blocking Sets--Dispatching on Electric
Railways

REVIEW QUESTIONS Page 359

INDEX Page 373

[Footnote A: For professional standing of authors, see list of Authors
and Collaborators at front of volume.]

[Footnote B: For page numbers, see foot of pages.]

[Illustration: PORTION OF TERMINAL ROOM OF LARGE COMMON-BATTERY OFFICE
Prospect Office, New York Telephone Co.]

CHAPTER XXII

THE SIMPLE COMMON-BATTERY SWITCHBOARD

=Advantages of Common-Battery Operation.= The advantages of the
common-battery system of operation, alluded to in Chapter XIII, may be
briefly summarized here. The main gain in the common-battery system of
supply is the simplification of the subscribers' instruments, doing away
with the local batteries and the magneto generators, and the
concentration of all these many sources of current into one single
source at the central office. A considerable saving is thus effected
from the standpoint of maintenance, since the simpler common-battery
instrument is not so likely to get out of order and, therefore, does not
have to be visited so often for repairs, and the absence of local
batteries, of course, makes the renewal of the battery parts by members
of the maintenance department, unnecessary. Another decided advantage in
the common-battery system is the fact that the centralized battery
stands ready always to send current over the line when the subscriber
completes the circuit of the line at his station by removing his
receiver from its hook. The common-battery s