The telephone system of the British post office. A practical handbook (1901)
Herbert, Thomas Ernest · London, New York, Whittaker and Co. · leaf 74
-Springs and Pegs. 59 magnet holds up an iron shutter. When the current is stopped thisshutter falls, calling the operators attention to the circuit. A smallmagnetised needle is also added, and this indicates when a current isflowing through the electro-magnet, and it is upon this that the ring-off… … The switch-springs consist of two springs Sj and Sj (Figure 45), restingupon two contact points, A and B. The upper spring S^ is cleft in order topermit the insertion of the peg. The springs curve backwards, and arefitted upon the back of the bo,ard by means of screws.
Telephone · Postal service
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