. The telephone system of the British post office. A practical handbook . ujre 128. Each subscribers line terminates upon a switch-spring and an indicator. The switch-springs are acommodated at the top Indicators and Switch-Springs. i6i of the board, and it will be observed that there are six rows of ten extra switch-springs are provided for various junction circuits,should they be necessary. Similarly the five indicators below the fiftysubscribers indicators are provided for similar purposes. The pairs ofcords are placed upon a, small shelf above the indicators and below theswitch-s
. The telephone system of the British post office. A practical handbook . ujre 128. Each subscribers line terminates upon a switch-spring and an indicator. The switch-springs are acommodated at the top Indicators and Switch-Springs. i6i of the board, and it will be observed that there are six rows of ten extra switch-springs are provided for various junction circuits,should they be necessary. Similarly the five indicators below the fiftysubscribers indicators are provided for similar purposes. The pairs ofcords are placed upon a, small shelf above the indicators and below theswitch-springs, the object being to avoid the cords crossing in front ofand thus obscuring the view of the indicators. The last row of tenindicators are for the ring-off signals, and upon the shelf below theseindicators are placed the ringing and speaking keys. The subscribers hnes terminate upon five-point switch-springs, the innersprings of which are connected to low resistance (loo ») indicators, theform of which is indicaftd in Figure 129. It consists of an electro-magnet. Earth Figure 129. A B with a small iron armature C carrying a lever D pivoted in front ofit. The lever catches the pivoted shutter E, which falls forward whenthe armature C is attracted. Upon a brass disc, normally covered by theshutter, the subscribers number is painted in black figures. It may bementioned that these indicators occupy about one square inch , the subscriber turning the crank, discloses his number at theexchange. The ring-off indicators, which are in circuit whilst subscribers are con-versing, are of the tubular form, very similar to the back coil of the self-restoring indicator, but much smaller and more compact. Of these thereare ten, one for each pair of cords. The indicators are covered with anouter iron sheathing to prevent overhearing from one circuit to anotherma the contiguous indicators. The low resistance line indicators are notin circuit during conversations, and therefore do
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Keywords: ., bookcentury1900, bookdecade1900, booksubjecttelepho, bookyear1901
