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actuated alarm circuit alternating current apparatus armature is attracted arrangement attendant's telephone battery BA bell circuit burglar alarm cable calling station cells CENTRAL BATTERY SYSTEM centre coloured common wire completed conductors connected cord cord circuit current flows current then flows depressed desk sets diagram direct current electro-magnet energizing fitted fixed fuse gong holes indicator board induction coil inserted installation insulated internal connexions iron joined in parallel junction box latter Leclanche cells line wires local battery magneto bells manually restored ment metallic method mounted necessary negative pole nexions normally ohms operator pair of wires permanent magnets plug board plug SP pole of battery position primary battery push push-button relay retardation coils ringing battery ringing key screw shown in Fig side of battery signal speaking battery speaking circuit spring switch switch-hook switchboard tele thence top contact transmitter trembling bell twisted usually vibration voltage whilst winding wishes to call wound