264,229. Automatic Telephone Manufacturing Co., Ltd., and Tench, F. Oct. 13, 1925. Addition to 227,510. Automatic and semi-automatic exchange systems; metering.-Relates to systems of the kind described in the parent Specification, in which dialling impulses are sent over the two speaking conductors in series whilst when all the setting operations have been completed circuit changes are effected to enable supervisory signals to be sent over the speaking conductors independently. The present invention consists in the application of this feature to a system employing forward loop dialling and is described with reference to a multi-office system comprising both automatic and manual exchanges. Full automatic and semi-automatic calls, and calls to an inquiry operator, are described in detail, the supervision in general being effected in the same manner as in the parent Specification by a marginal relay and a non-marginal relay which are connected in series to one of the speaking wires on the completion of dialling. The response of the non- marginal relay alone is used to repeat busy flash or hold the switches under the control of an operator, whilst the response of both relays effects metering. For semi-automatic working, the operator's selector requires only one such relay to give the operator answering supervision. Talking current is fed to the called party from the first local selector. According to a further modification, the supervisory relays are connected in turn to one of the speaking conductors, preferably by a slow-release relay which is energized at the end of dialling and is de-energized by the response of the supervisory relay which is connected up first. First selector-repeater, Fig. 1. This operates in the usual manner in response to the first digit and selects an idle two-wire trunk 51. 52 to an incoming selector-repeater, Fig. 2, at the wanted exchange. The release relay 8 in addition to its normal functions closes a circuit for the upper winding of a relay 17, which at armature 19 cuts out a retard 18 and substitutes a low non-inductive resistance to improve the impulse repeating circuit, and on the response of the switching relav 28 energizes over its lower winding in series with the forward loop including the two-wire trunk 51, 52 and the bridged line relay 53, Fig. 2, at the incoming selector. Incoming selector-repeater, Fig. 2. The release relay 56 closes a circuit for the upper winding of a relay 64, which performs similar functions to the relay 17 of the first selector, Fig. 1, but in addition directly bridges the line relay 53 across the incoming trunk. The next impulse series is repeated over the forward loop at armature 6 of the line relay 5, Fig. 1, the parallel relay 13 pulling up during impulsing to hold relay 17 over its upper winding and shunt its lower winding from the impulsing circuit. The incoming selector operates in the usual manner to find an idle trunk in the selected level, the switching relay 74 completing a forward loop to the intermediate (selector including the lower winding of relay 64. Intermediate selector. The next impulse series is repeated by the line relays 5, 53 to this selector which is arranged and operates in the standard manner with the exception that the line relay is bridged across the incoming trunk. The switching relay extends the incoming speaking conductors and the earthed guard wire to the connector, Fig. 4, the circuit of the lower winding of the relay 64 at the incoming selector now extending over the forward loop including a bridged line relay 144 of the connector. Connector, Fig. 4. The last two digits are repeated to the line relay 144 of the connector which operates in well-known manner. Busy test. If the wanted party is busy, the busy relay 159 locks up, and on the relapse of relay 163 the forward loop is interrupted at armatures 160, 164, and busy tone and intermittent battery are connected to the lower trunk conductor through a high resistance. The opening of the forward loop de-energizes relay 64, Fig. 2, which connects the supervisory relays 82, 87 to the lower trunk conductor, opens the bridge over relay 53 and connects this relay between the upper conductor 51 and earth. Relay 17, Fig 1, in the first selector thereupon relapses and connects supervisory relays 36, 40 to the lower conductor. When busy flash battery is applied at the connector, a circuit is completed for the lower winding of relay 82 and for relay 87, but owing to the inclusion of the resistance only the relay 87 responds and repeats flashing battery over retard 91, resistance 86, and the lower conductor 52. Owing to the inclusion of resistance 86, relay 36 at the first selector does not energize and the metering wire 4 is not grounded. The calling subscriber, hearing the busy tone, hangs up and release occurs as described subsequently. Completion of connection. If the wanted line is free, switching relay 168 locks up over its lower winding, opens the bridge. through the line relay 144, and connects up ringing current the calling party receives tell-tale ringing over by-pass condenser 176. The opening of the forward loop results in the relapse of relays 64, 17 and the connection of the supervisory relays 82, 87, 36, 40 to the lower trunk conductors as described in the previous paragraph. When the called party answers, ringing is cut off and the connection completed in the usual manner. Metering. On the response of the ringing trip relay 155, a circuit is closed over retard 65, Fig. 2, and the called loop, for the supervisory relays 82, 87 both of which operate, the former locking over its upper winding and shunting the resistance 86, and the latter short-circuiting the lower winding of relay 82 to balance the speaking circuit, and connecting battery over retard 91 to the lower conductor 52. The supervisory relays 36, 40 in the first selector both respond and perform similar functions, the relay 36 also grounding the wire 4 to meter the call. Talking current. This is supplied to the calling party over line relay 5 and to the called party over retard 65 and relay 87 at the incoming selector. Release. When the called party hangs up, relays 87, 40 de-energize. The relay 40 may be used to control a supervisory lamp to signal an attendant if the calling party omits to hang up. When the calling party replaces his receiver, the relapse of the line relay 5 releases the first selector and opens the forward loop to the incoming selector, the line relay 53 of which relapses and initiates the release of this switch. The removal of ground from the holding wire releases the subsequent switches in the usual manner. All trunks busy. If any of the selectors takes an eleventh rotary step, the switching relay is energized, but no holding circuit is completed for relay 17 or 64, which de-energizes and effects the change to supervisory condition. Cam springs are also closed to connect busy tone and flashing battery to the lower speaking wire. Connection to enquiry operator. This might be obtained direct from the bank of the first selector, but in the present case the calling party is extended to an operator's position, Fig. 7, over a first selector, Fig. 1, an incoming selector, Fig. 2, and an intermediate selector, in the manner previously described. When the connection is switched through at the intermediate selector to the trunk conductors 301, 302, Fig. 7, the relay 303 is energized over the upper trunk conductor, but since there is no battery connection on the lower conductor 302, the relays 64, 17 relapse and connect up the supervisory relays at the incoming and first selectors. Relay 303 lights a calling lamp 314 and connects up telltale ringing current over the lead 312. The operator plugs in, energizing sleeve relays 308, 315, the former of which extinguishes lamp 314 and cuts off the ringing, whilst the latter lights a supervisory lamp 319. If the calling party is still on the line, an impedance 313 is bridged across the jack springs and the supervisory relays 317, 320 are energized and the lamp 319 extinguished. Relay 308 also connects battery over retard 306 and resistance 307 to the lower conductor 302, the inclusion of the resistance causing the supervisory relay 87 only at the incoming selector, to respond. Battery through the retard 91 and resistance 86 is thereby connected to the lower conductor 52 and an auxiliary holding circuit under the operator's control is completed for the release relay 56. Similar operations take place at the first selector, Fig. 1. When the calling party hangs up, relays 5, 56, 303, 317 de-energize and the lamp 319 is lighted. The operator takes down the plug, causing the relapse of relays 308, 87, 17, 56, 8 and the release of the connection. Semi-automatic working. A call from a manual subscriber is extended from an operator's position, Fig. 5, over an operator's selector, Fig. 6, at which only one supervisory relay 284 is provided since the operator meters the call. On the subscriber removing his receiver, the operator inserts her answering plug PI, ascertains his requirements, and inserts the calling plug P2 into the jack J2 of an idle outgoing trunk. A lamp 210 is energized in series with a sleeve relay 204 which lights a busy lamp 206, and the operator throws her dialling key K thereby closing a circuit over the off-normal and impulse springs 202, 203 of the dial for the line relay 253, Fig. 6. The release relay 256 closes a circuit for the upper winding of relay 265 and connects battery to the lower trunk conductor 252 to hold the line relay 253 when the off-normal dial springs 202 open. The operator now dials the wanted number, and the selector, Fig. 6, operates in known manner, the energization of the switching relay 275 closing a forward loop to the switch ahead over armatures 270, 255, 276 and the lower winding of relay 265. Subsequent digits are repeated to the succeedi