. The telephone system of the British post office. A practical handbook . ent current, thus dropping the exchange automatic signalling is one of the distinctive features of the PostOffice system. The relay at the subscribers end is biassed against the permanentcurrent passing through it, and in order to effect a ring the exchangeclerk joins a battery to the line, which combines with the subscribersbattery, thus overcoming the bias upon the relay and closing the localcircuit. The path of this local circuit is from the split of the battery toterminal 6, thence through the bell to
. The telephone system of the British post office. A practical handbook . ent current, thus dropping the exchange automatic signalling is one of the distinctive features of the PostOffice system. The relay at the subscribers end is biassed against the permanentcurrent passing through it, and in order to effect a ring the exchangeclerk joins a battery to the line, which combines with the subscribersbattery, thus overcoming the bias upon the relay and closing the localcircuit. The path of this local circuit is from the split of the battery toterminal 6, thence through the bell to terminal 8, to the contact screw ofthe relay, and through the tongue back to the negative pole of thebattery. 6i Operating Connections. It will now be as well to consider the operators apparatus. Thespeaking apparatus consists of a Deckert transmitter and a watch receivermounted upon a suitable handle (Figure 51). This handle is soarranged that when the receiver is placed to the ear the transmitter facesthe mouth, and from what has already been said in reference to the. Figure 51. vertical positions of granular transmitters It will be seen that theinstrument should be held on a level with the nose, the head being heldup. There is also a button placed upon the handle, arid this button servesto short-circuit the secondary of the induction coil, thus leaving thereceiver in circuit, but cutting out the transmitter, and thereby preventingthe operators breathing or conversation being overheard by subscribersengaged in conversation. It is also necessary to make provision for ringing subscribers, and it willperhaps be most convenient to consider this first. A brass lever, pivotedat the back of the tablet and mechanically connected to a divided leversomewhat similar to that of a telegraph double-current key, protrudesfrom the front of the switch-board. Two spiral springs (Figure 52) holdthis lever down upon two contact springs, and in this position the dividedlever joins up the speaking
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Keywords: ., bookcentury1900, bookdecade1900, booksubjecttelepho, bookyear1901
