257,662. Automatic Telephone Manufacturing Co., Ltd., and Tench, F. June 4,1925. Automatic exchange systems.-Several district offices are given access to the same register controllers, which are provided with means operated in accordance with the trunk over which they are seized, whereby if the code dialled is that of the originating office the register controller is released and the call is completed locally. A district-office subscriber on making a call is connected by his line switch to a repeater R associated with hunting switches L, M. T. The switches L. T hunt respectively for an idle local selector and a direct trunk to a toll operator without however seizing such lines, while the switch M seizes a two-wire trunk terminating at the main office in a first code selector with a lateral connection to a hunting switch SS which selects an idle A-digit switch giving access to code-translating register controllers of the general type described in Specification 194,580. If the code dialled corresponds to another office, the register controller controls the setting up of the connection in known manner. and when it has received the full number of digits, sends back a signal to the repeater to prepare supervisory circuits and open the hunting circuits of switches L, T. If however the 1oca1 code or the toll code is dialled the register controller at once sends back a signal to the repeater to cause the call to be extended over the switch L or T and the main office apparatus is release. The register controller is provided with a group of relays 256 - - 259, one of which, as determined by a characteristic resistance associated with the incoming trunk, locks up to enable the register controller to discriminate between local and other calls. Registration of wanted number at the main office. When the repeater R is seized line and release relays 5, 9 and relay 39 complete driving circuits for the magnets 20, 26, 32 of the switches L, M, T. When the switch M finds an idle main office trunk, relay 21 switches through and relays 43, 46 pull up over the a- and b-wires, and hold up relay 39. In the main office, relay 91 pulls up over the incoming a-wire and starts the switch SS in search of an A-digit switch DS. When relay 94 switches through, relay 91 falls back and relays 43, 46 are now held in series with line relay 115. Dialling tone may now be sent back and the first digit is repeated by relays 5, 115 to the vertical magnet 133 of the switch DS which acts like a group selector to select a register controller. Dialling relay 33 replaces relays 43, 46 by a direct bridge but holds relay 39. When relay 132 switches through relay 171 pulls up. The remaining digits are repeated by relay 115 to the magnets 202, 201 of the office register and to the digit registers (not shown) over wiper 166 of switch 105, the magnet 162 of which receives an impulse timed by relay 157 when relay 152 falls back at the end of each digit. Transmission by register controller. In its third position, switch ICS connects up the marking ground to wiper 170 of the sender control switch OCS and completes an interrupter circuit for the magnet 183 of the sending switch SCS which at its first step energizes pick-up relay 175. At each subsequent step until the energization of stop relay 179 impulses are sent out over the trunk from springs 185 controlled by the stepping magnet. The stop relay as usual allows the switch OCS to take a step, drives the sending switch home, and is then released by the pick-up relay to initiate the transmission of the next digit. To guard against slow dialling the stop relay has an alternative circuit over normal contacts of the digit registers. The switch OCS is driven past blank positions in the case of short codes in a circuit 164, 170, 224, 168. Supervision and metering of main office calls. When the number is completely registered, ground impulses timed by relay 157 are sent back from wipers 163, 165 to relays 113, 111. which disconnect relay 115 from the loop and hold it locally. Relays 43, 46 thereupon fall back followed by relay 39 which connects up in their place the electropolarized supervisory relay 37 which later, when the wanted party replies, controls the meter over 4. Relay 39 also disconnects the magnets 30, 32 to prevent useless hunting. Release of register controller. When the number has been sent out, wiper 170 grounds the wire 149 to energize relay 80 which locks up and switches through to the talking switches. Relays 115, 118 fall back, energizing release magnet 122 and releasing relays 94, 132, 171. The latter relav drives switch OCS home and energizes the release magnets of the register and the switch ICS. Discriminating relays. Each register controller has a marginal relay 256 - - 259 for each district office. Each of these relays has a different operating margin and they are arranged in order of sensitiveness from right to left. The trunks from a particular district office are provided with a characteristic grounded resistance 100 which is connected by the dialling relays 123, 152 to the lead 155. Accordingly when the second digit is dialled, relay 256 pulls up, locks itself, and connects 155 to the next relay 257. If the resistance 100 is low enough, relay 257 locks itself, unlocks relay 256. and connects 155 to relay 258 and so on. At the end of the office code therefore one only of the relays 256 - - 259 remains locked up depending on which district offices is calling. Toll calls. If a district office subscriber calls TOL the register CS is set to the terminals 212, 215, and one of the relays 256 - - 259 is operated, and lead 151 is thus grounded when wiper 164 reaches its 3rd position. Relay 113 pulls up and releases relay 43, and since relay 46 is held, switching relay 27 pulls up, locks itself, extends the loop 43, 46 to the selected toll operator's position to give a signal, and releases relav 21, whereupon relays 115, 118 fall back and release the main office apparatus. Release control may be given to the operator by providing an alternative circuit for relay 9 over a back contact of relay 43 and front contact of relay 46, relay 43 being released at the will of the operator by grounding the a-wire. Alternatively relay 27 can be made to release relay 39 to put the supervisory relay 37 across the line. Local calls. The jumpering at the frame IDF is such that if a district office dials its own code the marking ground is connected by wiper 203 to the wire 150 to energize relay 111. Relay 46 is thus relased but relay 43 is held and relay 15 extends the call to the preselected local selector, locks itself to ground returned by the latter, and cuts off relays 5, 21, whereupon relays 9, 43, 46, 39 fall back and the main office apparatus is released. Digit absorbing. Digit absorbing selectors may be provided in the district office or the switch-over signal from the reigster controller may be delayed until it has registered one or more useless subscriber digits, e.g. by making the jumper between the 3rd and 4th terminals of wiper 164 include a back contact of one of the relays 256 - - 259. Modifications. The switches L, T may be made to seize their lines and release them when relay 39 falls back or the switch T may hunt only after the switch-over has taken place. The Provisional Specification descends a similar system but the repeater has no relay corresponding to 39. The relays 43, 46 are initially energized by the dialling relay and lock up over additional windings and the two wires of the trunk in series with the two windings of the line relay of the A-digit switch, which is in this case permanently associated with the trunk. The release of the relays is brought about by shortcircuiting their locking windings. Both relays are released to connect up the supervisory relay when the register controller has completed its opration. It is suggested that the signals from the register controller might take the form of current reversals. Where the district office has no direct trunks to a toll operator the register may have two groups of relays 256 - - 259 reached respectively over wipers 144, 145.