212,640. Siemens Bros. & Co., Ltd., and Berry, J. Dec. 14, 1922. Automatic exchange systems; party line systems.-In the case of a revertive call in a partyline system, the calling subscriber on receiving a busy signal hangs up or otherwise breaks the loop. The connector is thus released simultaneously at both ends, and a relay D is energized, preventing restoration to normal and causing ringing of the wanted subscriber. In the first and second arrangements (Figs. 2 and 3), a relay B operates over the a and b connector wipers and the calling loop and energizes a sluggish relay C which relapses after the relay N is released at the preceding switch. In the third arrangement (Fig. 4), a relay PA operates over the connector test wiper when the line switch is restored to normal and holds the relay C until the relay N falls back. First arrangement, Fig. 2. Upon seizure of the connector, relay N energizes in series with the test relay of the preceding selector and locks itself, while the line relay A energizes over the b wire and contacts tr3, p3, s4 and operates sluggish relay V over contacts p1, n2, a1, k3, w1, preparing the circuit of the vertical magnet H to which impulses are repeated over back contact a<2>, relay V being held over back contact a<1> until the end of the train, whereupon it releases and energizes switch-over relay E over contacts p1, n2, v1, k3, w1, connecting up the rotary magnet R and again operating relay V over contact e4. Relay V is held as before and relapses at the end of the train of impulses, and sluggish relay E falls back after an interval, so that the test relay P is momentarily connected over contacts v2, e3, tr6 to the c wiper. Busy signal and release. If the called line is engaged, relay P does not, operate, and upon release of relay E, sluggish relay TR energizes over its winding 1 and contacts e1, a3, w2, opencircuiting relay A and sending back busy tone from the transformer 24. Relay B energizes over the called subscriber's loop without effect. Upon hanging up by the calling subscriber, the preceding switches are restored, and relay N falls back, connecting up the release magnet over contacts p1, n2, k2. Ringing current. If the called line is free, relay P energizes over the line switch cut-off relay and locks over its low resistance winding 2 and contact n3, marking the called line busy. Relay P also connects the a and b leads to the called line and open-circuits the line relay A, shortcircuiting winding 1 of relay TR over contacts a3, tr1, so that relay S is energized to send ring- ing current over the line over interrupter contacts 20, contacts of relay F and winding 2 of relay TR. The apparatus is adapted to serve party lines with two subscribers only on a line with leg ringing, connectors serving one set of subscribers being as shown, and those serving the other set having the connections to front contacts s3, s4 reversed to connect the ringing generator to the a wire. When the called subscriber replies, relay TR is energized by increased current through its winding 2, and substitutes its winding 1 in place of relay S, and is held thereby until the connector is released. Revertive party line calls. Relay TR energizes and transmits busy tone, and relay B energizes in this case over the a and b connector wipers and the calling subscriber's loop and operates sluggish relay C. The calling subscriber hangs up, releasing relay B, so that sluggish relay D operates and locks, since relay N is released at the preceding switch before relay C falls back. Relay E energizes over its winding 2 and contacts p1, n2, d2, releasing relay TR, so that the test relay P operates over contacts d3, tr6, e3, v2 and the cut-off relay of the line switch which is now in normal position, completing the connection and connecting up the ringing relay S upon relapse of relay E. Relay F is energized intermittently over interrupter contacts 25 and contact d4, and causes the two party line subscribers to be rung alternately, interrupter contacts 26 being provided to connect the generator to the front contacts of the relay. Relay TR operates on the reply of the called subscriber and connects relay B to the line to supply speaking current and lock relay P. Release is initiated by the relapse of relay B, and the release magnet circuit is completed upon falling back of relay P. Second arrangement, Fig. 3. Code ringing is employed, and the code to call the wanted subscriber is selected by a switch D1-4 operated by an extra train of impulses. Upon release of relay V at the end of the units impulse train, relay L is energized over wiper D4 and contact w2, locking, transferring the operating circuit to the code switch magnet CD and energizing relay V again over wiper D2. Relay V releases at the end of the impulse train, and the connection then proceeds as before. Ringing current is sent over wiper D1 and the selected interrupter spring 28 which is controlled by a rotating cam 27. During release the magnet CD is connected up over interrupter 30, contacts p6, d4, n7 and wiper D3, and restores the code switch. A revertive party line call is set up as in the first arrangement. Third arrangement, Fig. 4. A non-revertive call is set up in the same way as in the first arrangement, leg ringing being employed for the two subscribers on a party line as shown in Fig. 1. Revertive party line calls. Since the line tests busy, relay TR energizes on the relapse of relay E and connects up sluggish relay C over contacts p4, n2, pa2, tr4. When the calling subscriber hangs up on receiving the busy signal, relay PA energizes over the connector test wiper in series with the cut-off relay of the line switch and locks over its winding 1 and contacts a2, pa1, tr5. Before relay C falls back upon relapse of relay N, sluggish relay D energizes over its winding 1 and contacts p4, n2, c2, pa2, tr4, locking and connecting up relay E over contacts p4, n2, c2, d4, c3. Relay TR is thus released and removes a short-circuit across winding 2 of relay P so that it energizes over the test wire, connecting through the a and b wires, releasing relay E and holding relay D over its winding 2. The ringing relay S operates, and relay F energizes intermittently over its winding 2 and contacts d6, pa4, so that both subscribers are rung. Relay TR operates upon reply of the called subscriber and shortcircuits relay S. Current is supplied over winding 1 of relay F and relay A, relay PA being released and relay D being held at contact a2. Upon release, relays A, D, P de-energize in turn, completing the release magnet circuit. Modification using harmonic ringing, Fig. 4. In this case relay F is not required, and its winding 1 is replaced by a retardation coil. Contact s3 is connected to earth and contact s4 over winding 2 of relay TR to the spring set associated with a generator of the frequency for ringing the set of subscribers accessible over the connector. Substation apparatus, Fig. 5. A key 49 is provided whereby the metallic loop may be opened without the necessity of hanging up, ccnnecting the receiver 41 across the line in series with a resistance 50 and a condenser 45.