rties who are using it, and finding
out what the emergency call is for. If the operator finds that the
subscriber has misused this privilege of making the emergency call,
she may restore the connection to the parties previously engaged in
conversation.

One of the salient points of this Roberts system is that the operator
always has control of the line. A subscriber is not able even to use
his own battery till permitted to do so. A subscriber who leaves his
receiver off its hook in order that he may be signaled by the operator
when the line is free, causes no deterioration of the local battery
because the battery circuit is held open by the switch contacts
carried on the ringer. It cannot be denied, however, that this system
is complicated, and that it has other faults. For instance, as
described herein, both sides of the line must be looped into each
subscriber's station, thus requiring four drop, or service, wires
instead of two. It is possible to overcome this objection by placing
the line relays on the pole in a suitably protected casing, in which
case it is sufficient to run but two drop wires from the nearer line
to station. There are undoubtedly other objections to this system, and
yet with all its faults it is of great interest, and although radical
in many respects, it teaches lessons of undoubted value.

CHAPTER XVIII

ELECTRICAL HAZARDS

All telephone systems are exposed to certain electrical hazards. When
these hazards become actively operative as causes, harmful results
ensue. The harmful results are of two kinds: those causing damage to
property and those causing damage to persons. The damage to persons
may be so serious as to result in death. Damage to property may
destroy the usefulness of a piece of apparatus or of some portion of
the wire plant. Or the property damage may initiate itself as a harm
to apparatus or wiring and may result in greater and extending damage
by starting a fire.

Electrical currents which endanger life and property may be furnished
by natural or artificial causes. Natural electricity which does such
damage usually displays itself as lightning. In rare cases, currents
tending to flow over grounded lines because of extraordinary
differences of potential between sections of the earth's surface have
damaged apparatus in such lines, or only have been prevented from
causing such damage by the operation of protective devices.

Telegraph and telephone systems have been t