the coil of the line relay to another common wire
_2_, which connects with the live side of the common battery. Obviously,
therefore, this arrangement corresponds with that of Fig. 309, since the
battery may furnish current to energize any one of the line relays upon
the closure of the circuit of the corresponding line. Each of the relay
armatures in Fig. 310 is connected to ground.

Here we wish to bring out an important thing about telephone circuit
diagrams which is sometimes confusing to the beginner, but which really,
when understood, tends to prevent confusion. The showing of a separate
ground for each of the line-relay armatures does not mean that literally
each one of these armatures is connected by a separate wire to earth,
and it is to be understood that the three separate grounds shown in
connection with these relay armatures is meant to indicate just such a
set of affairs as is shown in connection with the tip-spring anvils of
the jacks, all of which are connected to a common wire which, in turn,
is grounded. Obviously, the result is the same, but in the case of this
particular diagram it is seen that a great deal of crossing of lines is
prevented by showing a separate ground at each one of the relay
armatures. The same practice is followed in connection with the common
battery. Sometimes it is very inconvenient in a complicated diagram to
run all of the wires that are supposed to connect with one terminal of
the battery across the diagram to represent this connection. It is
permissible, therefore, and in fact desirable, that separate battery
symbols be shown wherever by so doing the diagram will be simplified,
the understanding being, in the absence of other information or of other
indications, that the same battery is referred to, just as the same
ground is referred to in connection with the relay armatures in the
figure under discussion.

Each line lamp in Fig. 310 is shown connected on one hand to its
corresponding line relay contact and on the other hand to a common wire
which leads through the winding of the pilot relay to the live side of
the battery. It is obvious here that whenever any one of the line relays
attracts its armature the local circuit containing the corresponding
lamp and the common battery will be closed and the lamp illuminated.

Whenever any line relay operates, the current, which is supplied to its
lamp, must come through the pilot-relay winding, and if a number of line
relays are