330,626. Standard Telephones & Cables, Ltd., and Haigh, L. B. March 13, 1929. Semi-automatic exchange systems.-In a network of rural offices connected in tandem chains to a main exchange at which an operator sets up all connections, connections are extended by the operator over a bypath or marking switch at each office, and on completion, a speaking path over a link-circuit at the furthest possible office from the main exchange is substituted, and the operator is automatically disconnected from the conversing parties. In the system described, a call originating, for example, in the office B is extended over finder JSB and junction circuit and junction JB, JLP to office A from which it is extended .in similar manner to the main exchange D. To set up a call to any one of offices A, B, BB, C, the operator siezes a control circuit and marking switch RA, RSA at office A and dials the first digit. If the wanted party is in B or C, this digit signifies a group of junctions A-B one of which has been seized by the calling party, and RSA hunts for this junction. The control circuit and marker RB, RSB at B are taken into use and, if the wanted party is in B, RB is set by two digits on to terminals of the wanted line whereupon SBl in the link circuit steps to the calling line as determined by JSB, and SB2 steps to the wanted line marked by RSB. The operator is disconnected in JB from the speaking path and, on receipt of a signal, withdraws so that the junctions JLA, JLB and switches in the setting path are released. If the wanted party is in office C, the operator proceeds as before but RSB responds to the second digit and hunts for an idle junction B-C. The marker RSC at C is set by two further digits, the speaking connection is set up over SB1 in the link circuit at B to the calling party and over SB2 at B and JSC at C to the called party, the marker at C being released automatically, and the other setting apparatus released, as before, when the operator withdraws. If the wanted party is in office BB, RSA responds to the first digit and hunts for a junction to BB whereupon RSBB is set on terminals of the wanted line. In this case the link circuit at A provides the speaking path which extends over SA1. JSB to the calling party and over SA2, JSBB to the called party. The control and marking circuit shown in Fig. 4 comprises a marking switch having banks +, -, TC, S, a control bank R, and a homing bank. In the modified circuit shown in Fig. 5, increased capacity is provided by using switches P (+, -, R, H) and M (S, TC, R, H) both ultimately set on terminals of wanted line.. Switch P responds to the first digit, M steps to .the group contact marked by P and shunts for an idle outlet or responds to the second digit, whereupon P steps on to correspond with M. The calling party is disconnected from the operator while she is setting up the connection, but may be reconnected at any time at the will of the operator. The operator may break in on an established connection to offer a call. The rural offices are also provided with circuits, Fig. 10, for disconnecting the local battery and extending an alarm to the operator in case of faults, and with call offices, Fig. 3, as modified by dotted line circuits. The marking, link and junction circuits shown in full lines in Figs. 4, 6 and 7 are used at non-tandem offices BB, C. At tandem offices A, B the dotted line connections are added and connections indicated x are. omitted; also, as A has two groups of tandem lines relays GG and HH are equipped but not FF, whereas at B there is only one group and FF is equipped but not GG, HH. Call from tandem office B to main exchange D. The line relay AL, Fig. 3, operated by calling subscriber's magneto locks over ST to common start relay O and connects battery to the test terminal TC in the banks of finders JS, Fig. 7. Relay 0 grounds the lead l to operate relay KS of the first idle junction. The circuit of magnet DM is now completed and when finder JS reaches the calling line, SH energizes, locks over sh6, t7, grounds the test wiper to busy the line and short-circuit the holding winding of AL, connects battery over PJ, BA to the lower leg of the junction, and at sh2 extends the start lead to the next junction. Relays AL, O and KS fall back. At the incoming end of the junction, Fig. 8, relay L operates over the lower leg, relay BA at the outgoing end remaining inert, grounds the start lead ST to the register at office A, and connects battery over CO to the test terminal. A finder at office A hunts for the calling junction in a manner similar to that described above with reference to Figs. 4 and 7, but the holding arrangements for the test relay SH are modified since relays AC, T, Fig. 7, are operated at office A. When the calling junction is found, SH grounds the test wiper to operate CO which locks up and releases L and relays O, KS fall back as before. L and KS are slow to release and R holds initially over ks3, but during the release time of L, the S terminal of the finder is grounded to operate T which locks to ground at t1 and connects the ground over eb3, sh8 to AC, and H finally locks to ground at t7. At the incoming end of the junction at the main exchange, Fig. 9, relay Y responds to battery over the lower leg and lights lamp CS, relay BA at office A remaining inert. The operator plugs into jack J1, and sleeve relay C releases Y, and connects high resistance battery over Z to the upper leg of the junction to operate RQ, Fig. 7, at office A, relay QR remaining inert. Relay EB pulls up, disconnects the battery from the lower leg which it connects over BA to RQ, and completes the circuit over the finder JS at A. High resistance battery over PJ and the upper leg of the junction to office B (relay T and A being operated) operates relay RQ at that office and relay EB pulls up to complete the speaking path. If the calling subscriber's receiver has been removed, ground over relay RQ at office B and the lower leg of the junction holds relay AC at office A operated, and ground over RQ at office A and the lower leg operates Y at the exchange D so that lamp CS is extinguished. If the receiver is still on the hook, ground over the hook operates AC at office B which disconnects ground from the lower leg of the junction to office A so that AC thereat falls back, disconnects ground from the lower leg of the junction to main exchange D and lamp CS glows. The operator rings the calling party by plugging into jack OJ and throwing the ringing key of.a cord circuit (not shown). Relays Y, Z are disconnected from the junction by sleeve relay D but strong battery over the tip of the plug holds RQ at office A and also operates QR which connects strong battery over PJ, t3, qr2 to the upper leg of the junction to office B to hold RQ and operate QR thereat. The upper and lower legs at office B are connected at qr2 (T being unoperated). The relays AC are disconnected at qr1 from the lower legs of the junctions but AC at office B holds to ground at t6. There is now a clean path for ringing current over the lower legs of the junctions through subscriber's bell as shown in full lines, or over both legs of the junction between A and B through the bell windings to a mid-point ground as shown in dotted lines. When the ringing key is restored relays QR at offices A and B fall back, and when the calling party responds, relay AC at office B releases and relay AC at office A operates. Relay Y, Fig. 9 pulls up and extinguishes lamp CS. The operator withdraws from jack OJ and completes the call over jack TJ in the usual manner. Release, normal and forced. When the calling party replaces his receiver, the relays AC, operating as described in the previous paragraph, complete a circuit for lamp CS, and the operator withdraws from TJ. Relay C, Fig. 9, falls back and removes battery from the upper leg to release the operated relays at offices A and B. If the operator withdraws before the calling party replaces his receiver, the connections at offices A, B are not broken down, since relay SH at A is held over front contacts ac2, t7 and relay SH at B is held over corresponding back contacts. Relay Y, Fig. 9, remains operated over BA, PJ, Fig. 7, and lamp CS glows to warn the operator. If the calling party does not replace his receiver, the operator forces release by withdrawing from TJ and plugging into OJ. The junction is disconnected from Y, Z and strong battery over the tip of the plug holds RQ at office A and operates QR with similar results at office B as previously described. The relay AC at A falls back and the corresponding relay at B pulls up so that the relays SH are only held over eb5. The operator releases relay D to remove battery from the upper leg of the main junction, and relays RQ, QR, EB, SH, T at office A fall back, and the consequent removal of battery from the upper leg of the tandem junction releases relays RQ, QR, EB, SH, AC at office B, relay AC being slow-torelease owing to a shunt, so that an alternative holding circuit for SH is not completed. Call between two subscribers on office B. The operator at exchange D called as previously described plugs into jack TJ, ascertains the wanted number, and inserts the setting up plug into jack OJ. The tip and ring of this plug are connected respectively to weak and strong battery so that when sleeve relay D connects the jack OJ to the junction, relay RQ at office A is held over the upper leg but QR remains inert, and relay BA, Fig. 7 operates over the lower leg to complete a circuit for impulse relay A, Fig. 4, of the register at office A. Relay B pulls up, removes ground from the start lead l to prevent operation of the finder JS, and operates SK, Fig. 7, which locks up, transfers the holding circuit of SH to lead q, and at sk9 releases relay BA, and connects impulse relay A to the lower leg of the junction, the positive leg being disconnected from QR which falls ba