Telephone Meter

—A device employed in a limited telephone service for recording the number of calls sent by a subscriber. Telephone Operation. Atmospherie sound waves strike the diaphragm of the. telephone and cause it to vibrate. The. vibrating dfaphragm produces a change in the magnetic field of the telephone. The changes in the magnet ice field induce currents in the wire coil of the telephone. The induced currents are transmitted from the transmitter telephone through the line to the receiver telephone. In the telephone receiver, the induction currents produce changes of intensity in the magnetic field. In consequence of these changes in the magnetic field, the diaphragm of the receiver is thrown into vibration. ' The vibrations of the diaphragm of the telephone receiver give rise to air waves, which are propagated to the tympanum of the ear.; Every time the human voice is used, vibrations of the air are produced, and the louder and higher the greater the number of vibrations: with each change of tone the diaphragm vibrates in sympathy.