h sleeve
contact is shown to be grounded. The talking circuit between the two
connected lines in this case may be traced as follows: From the
subscriber's station at the left through the right-hand limb of the
metallic-circuit line, through the tip contact and tip conductor of
the cord circuit, to the single limb of the grounded-circuit line,
thence to the sub-station of that line and through the talking
apparatus there to ground. The return path from the right-hand station
is by way of ground to the ground connection at the central office,
thence to the sleeve contact of the grounded line jack, through the
sleeve conductor of the cord circuit, to the sleeve contact of the
metallic-circuit line jack, and thence by the left-hand limb of the
metallic-circuit line to the subscriber's station.

[Illustration: Fig. 278. Connection Between Dissimilar Lines]

A better way of connecting a metallic-circuit line to a grounded line
is by the use of a special cord circuit involving a repeating coil,
such a connection being shown in Fig. 279. The cord circuit in this
case differs in no respect from those already shown except that a
repeating coil is associated with it in such a way as to conductively
divide the answering side from the calling side. Obviously, whatever
currents come over the line connected with the answering plug will
pass through the windings _1_ and _2_ of this coil and will induce
corresponding currents in the windings _3_ and _4_, which latter
currents will pass out over the circuit of the line connected with the
calling plug. When a grounded circuit is connected to a metallic
circuit in this manner, no ground is thrown onto the metallic circuit.
The balance of the metallic circuit is, therefore, maintained.

To ground one side of a metallic circuit frequently so unbalances it
as to cause it to become noisy, that is, to have currents flowing in
it, by induction or from other causes, other than the currents which
are supposed to be there for the purpose of conveying speech.

[Illustration: Fig. 279. Connection of Dissimilar Lines through
Repeating Coil]

_Convertible Cord Circuits._ The consideration of Fig. 279 brings us
to the subject of so-called convertible cord circuits. Some
switchboards, serving a mixture of metallic and grounded lines, are
provided with cord circuits which may be converted at will by the
operator from the ordinary type shown in Fig. 276 to the type shown in
Fig. 279. The advantage of