. The telephone system of the British post office. A practical handbook . its Terminated upon SwitchSections. 119 self-induction, and thus their resistance to a speaking current is enormouslyenhanced, and the speaking volume of sound, therefore, is not sensiblydiminished by their application. If now bridging coils are placed at either end of our circuit, we mayperform whatever signalling we choose over the centre of the loop withoutinterfering with the speaking round the loop. It is, of course, assumedthat the circuit is not faulty. One (Record Call Junction) circuit terminated upon a s
. The telephone system of the British post office. A practical handbook . its Terminated upon SwitchSections. 119 self-induction, and thus their resistance to a speaking current is enormouslyenhanced, and the speaking volume of sound, therefore, is not sensiblydiminished by their application. If now bridging coils are placed at either end of our circuit, we mayperform whatever signalling we choose over the centre of the loop withoutinterfering with the speaking round the loop. It is, of course, assumedthat the circuit is not faulty. One (Record Call Junction) circuit terminated upon a switch sectionis illustrated in Figure loi. It will be seen that the loop passes to the longand short springs of an eight-point switch-spring, the three top springs ofwhich are used for signalling, as in the case of the ordinary transfer the loop is placed, the bridging coils, the centre of which passesthrough a visual indicator to the middle spring. At the Companys .endthe circuit terminates upon a five-point switch-spring, the inner springs of Ro Figure 101. which are connected together to a visual indicator, having an earthedbattery joined to it. In the normal state of affairs, the negative pole ofthe battery A at the Post OiBce passes through the relay, bottom andcentral springs through the visual and along both lines in parallel. Thebattery B is exactly equal to the A, and as both have their negative polesto line, no current whatever flows through the indicators. At theCompanys end a special pair of cords having bridging coils with anearthed visual indicator across them is used for connecting subscribers tothe , circuit. Immediately a peg is inserted at the Companys endthe inner springs no longer make contact with the line springs, and inplace of this the lines are connected to the ring-off visual across the cords,and thus the circuit of the battery A is completed. This drops the PostOffice visual also, and the operators attention is thereby call
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Keywords: ., bookcentury1900, bookdecade1900, booksubjecttelepho, bookyear1901
