The telephone system of the British post office. A practical handbook (1901)
Herbert, Thomas Ernest · London, New York, Whittaker and Co. · leaf 34
through it. Du Moncel found that the nearer the mass ofan armature approached that of its magnet the greater was theirmutual attraction—i.e., the greater is the magnetic field between them ;consequently if having designed our ring and magnet upon these lines weplace our diaphragm between them we… … Figure g. The ring answers precisely the same purpose without affecting the flexibilityof the diaphragm, amd to this may be traced its greater efficiency. Themagnet is usually nickel-plated, and thus presents a very good appearance.
Telephone · Postal service
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