of which are left of sufficient length to be bent back around the
windings after they are in place and thus form a completely closed
magnetic path for the core. The windings of this particular coil are
four in number, and contain about 2,400 turns each, and have a
resistance of about 60 ohms. In this coil, when connected for local
battery work, the windings are connected in pairs in series, thus
forming effectively two windings having about 120 ohms resistance
each. The whole coil is enclosed in a protecting case of iron. The
terminals are brought out to suitable clips on the wooden base, as
shown. An external perspective view of this coil is shown in Fig. 110.
By bringing out each terminal of each winding, eight in all, as shown
in this figure, great latitude of connection is provided for, since
the windings may be connected in circuit in any desirable way, either
by connecting them together in pairs to form virtually a primary and a
secondary, or, as is frequently the case, to split the primary and the
secondary, connecting a battery between each pair of windings.

[Illustration: Fig. 109. Repeating Coil]

[Illustration: Fig. 110. Repeating Coil]

Fig. 111 illustrates in section a commercial type of coil designed
for talking through only. This coil is provided with four windings of
1,357 turns each, and when used for local battery work the coils are
connected in pairs in series, thus giving a resistance of about 190
ohms in each half of the repeating coil. The core of this coil
consists of a bundle of soft iron wires, and the shell which forms the
return path for the magnetic lines is of very soft sheet iron. This
shell is drawn into cup shape and its open end is closed, after the
coil is inserted, by the insertion of a soft iron head, as indicated.
As in the case of the coil shown in Figs. 109 and 110, eight terminals
are brought out on this coil, thus providing the necessary flexibility
of connection.

[Illustration: Fig. 111. Repeating Coil]

[Illustration: Fig. 112. Diagram of Toroidal Repeating Coil]

[Illustration: Fig. 113. Toroidal Repeating Coil]

Still another type of repeating coil is illustrated in diagram in Fig.
112, and in view in Fig. 113. This coil, like the impedance coil shown
in Fig. 104, comprises a core made up of a bundle of soft iron wires
wound into the form of a ring. It is usually provided with two primary
windings placed opposite each other upon the core, and with two
secondary wi