. The telephone system of the British post office. A practical handbook . —) 1 ) Figure 83. Eight-point switch-springs are used for the junctions between sections iand 3. The loop upon which the trunk is extended is kept perfectly freefrom apparatus of any description, and is joined to the two line signalling is accomplished by means of the three upper springs, and isquite automatic, the mere insertion of a peg throwing the Figure 84. The principle of the system is indicated in Figure 84, where a completecircuit is joined up in skeleton. The top and bottom springs, of the
. The telephone system of the British post office. A practical handbook . —) 1 ) Figure 83. Eight-point switch-springs are used for the junctions between sections iand 3. The loop upon which the trunk is extended is kept perfectly freefrom apparatus of any description, and is joined to the two line signalling is accomplished by means of the three upper springs, and isquite automatic, the mere insertion of a peg throwing the Figure 84. The principle of the system is indicated in Figure 84, where a completecircuit is joined up in skeleton. The top and bottom springs, of the twoswitch-springs are respectively connected to the positive and negative polesof the transfer battery. The two middle springs are connected together H 98 Actual Connections of Transfer Circuits. with the two visuals in series. In the normal condition the central springsat both ends are connected to the negative pole of the battery, and thusno current flows through the visuals. If now a peg is inserted at A thecentral spring is raised from the bottom to the top spring, where it is con-nected to the positive pole of the battery, and thus a current flows throughboth visuals. The path is from the positive pole of the battery to the topspring, to the centre spring and through both visuals to the lower .springat B [vid the middle spring at B) and thence back to the battery. Thusboth indicators show white. At A this indicates that there is no
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Keywords: ., bookcentury1900, bookdecade1900, booksubjecttelepho, bookyear1901
