| Repeating Coil

—In telephone work, a special form of induction coil designed to connect a grounded line with a metallic line. Repeating coils were formerly constructed on the principle of the Faraday ring, which consists of a coil of iron wire for the core with a bobbin carrying the primary winding on the one side and another carrying the secondary on the opposite side. Such an instrument is still known as the standard repeating coil, as generally used by the Bell companies. Later practice, however, has given birth to the armored | coil, which is enclosed in a suitable iron sheath, with the primary object of neutralizing stray currents and inductive influences from the outside by a magnetic envelope, end also of preventing similar influences from the coil itself upon outside apparatus. It consists e entially of ‘a primary and secondary coil wound upon a core consisting of a bundle of soft iron wires the ends of which are bent around outside the coil forming a casing of wire, or the coil is enveloped in an annealed iron tube, closed at both ends and connected to the core,