396,494. Automatic exchange systems. SIEMENS BROS. & CO., Ltd., Caxton House, Tothill Street, PATTERSON, W. G., 59, Grove Park Road, Mottingham, both in London, and LONG, D. P., 3, Ingleby Way, Chislehurst, Kent. April 4, 1932, No. 9611. [Class 40 (iv).] In a multi-office system, first selectors have access to a part of each group or each of some groups of direct inter-exchange junctions and to a group of overflow outlets leading to auxiliary selectors which give access to the remaining junctions of the groups. Tandem junctions for exchanges having indirect junctions or for re-routing when all direct junctions of a group are busy, may appear in the banks of the auxiliary selectors. In the system described, the first and auxiliary selectors are each associated with a common control and marking circuit, the selectors and markers being switches of the kind described in Specification 388,173 comprising staggered wipers driven over different levels in succession by an electric motor controlled by a latch magnet, the selectors having two sets of wipers. The control circuit of the selectors comprises three exchange-digit registers to control the setting of the marker which marks a group of direct junctions in the selector banks and also the overflow group if an overflow direct junction or an alternative route is available. If an idle direct junction is found, the control circuit is released. If not, and if there is an idle overflow outlet, the control circuit sends the exchange digits to registers in the control circuit of the auxiliary selector and also the first numerical digit which it has received on the A-digit register from which the A-digit had previously been transferred to a relay group. The control circuit of the auxiliary selector receives the remaining numerical digits direct, and sets its marker and the auxiliary selector. If a direct junction is found, the control circuit sends out the numerical digits immediately, but if a tandem junction is selected, the exchange digits are translated into routing digits which are sent out followed by the numerical digits. The first and auxiliary selectors may also give access to local trunks. Tandem junctions may appear in the banks of the first instead of the auxiliary selectors in which case apparatus for sending routing digits and storing and sending numerical digits is associated with the junctions. This arrangement is not described in detail. The control circuit of the first selector may store more than one numerical digit, the storing of one or more numerical digits being necessary to prevent loss since dialling may occur before the second control circuit is ready. The junction of each group may be spread over two or more groups of first selectors. Specification 220,364, [Class 40 (iv), Telephones &c.], is referred to. The Provisional Specification describes also (1) the application of the invention to routing over a by-path; (2) manual junctions with associated coding equipment appearing in the first selector banks, and (3) some direct junction groups appearing in the auxiliary selector banks only. Normal operation (direct outlet available). When the first group selector FJS is taken into use, relays A, B in the common control and marking circuit, Figs. 1 and 2, pull up followed by JB which removes the short-circuit from K(i) so that this relay energizes, locks over K(ii) and connects up the control circuit. The A, B and C digits are received by back-stroke switches AS, BS, CS in succession. The A digit may be 2 .. 9, digit 1 returns NU tone by the operation of SL(i) over AS2, while digit 0 obtains access to an operator as described in a subsequent paragraph. The A digit is repeated to magnet ASDM and series relay C and when C relapses, E pulls up over AS2 (positions 2 to 9), locks up, extends the impulse circuit to BSDM, and energizes latch magnet MLM which starts motor MDM of the marker FMS. When the marker reaches the the contact in FMS1 marked by cross-connection to AS3, test relay T pulls up and releases the latch-magnet MLM. FMS is now standing on first contacts of a group appropriate to the A digit. The B digit (2 .. 0) similarly operates switch BS but AS also takes a step at the end of the train (to release relay T) owing to the operation and release of magnet ASDM by series relay C. As switch BS passes position 2, magnet CSDM steps switch CS off normal and if the B digit-exceeds 5, CS is further driven by self-interruption to position 12. The registers are 25-point switches and all the B, C combinations may thus be accommodated on 5 banks of CS. The relapse of C at the end of the second impulse train also closes a circuit over BS4 for F(i) which locks up, transfers the impulse circuit to CSDM and completes a marking circuit over BS6 and FMS1. The' relapse of T energizes the latch-magnet. MLM so that FMS is driven to the B-digit marking whereupon T pulls up again to stop FMS at the commencement of a sub-group representing the A, B digits. If a non-existent A, B combination is dialled, FMS is unmarked for the B digit and proceeds to the first contact of the next A group which was marked by causing switch AS to take a step during the B digit. SL(ii) therefore pulls up over AS3 in series with T and connects up NU tone. Assuming reception of an existing code, discrimination is effected at this point as to whether the outlet is to be found in the first half-revolution of the group selector (full line wipers) or in the second half-revolution (dotted line wipers). If the outlet is in the second half, the contact on which FMS3 is standing is connected to relay PP(i) which locks up and operates latchmagnet FLM of the group selector FJS to release the driving motor FDM whereupon FJS proceeds to the first contacts of the dotted banks on which TA pulls up over rectifier R to release the latch magnet and stop the switch. In the meantime, the C digit (2 .. 0) comes into switch CS which takes up one of positions 2-10 or 14-22 dependent on whether the B-digit was 2-5 or 6-0. At the end of the train, the relapse of C operates G which transfers the impulse circuit to ASDM, connects up a differential winding PP(ii), Fig. 1, to release PP, and releases T to start up the marking switch FSM which proceeds until the reoperation of T over FMS2 and one of banks CS3. CS7 determined.by the setting of BS5. The re-operation of T also energizes TM(ii) which energizes the latch magnet FLM of the group selector and operates WS, Fig. 1, over FMS4 if the outlet is to be found over the second set of wipers of the group selector. Relay TM also causes AS to proceed by selfinterruption to position 13. The marking switch FMS is . now standing on contacts corresponding to the exchange code, and the contact in FMS6 is cross connected to a group'of contacts in bank FG or FG1 of the group selector. Motor FDM, being unlatched, now drives the group selector until an idle outlet in the marked group is reached whereupon battery on test wire FPW (or FPW1) over wipers FP,FG (or FP1, FG1 if WS is operated) and FMS6 operates relay TA to release the latch magnet. TD(i) operates in parallel with TA, reduces the potential on the test wiper to busy the outlet, holds over TD(ii) and operates switching relay H. The connection will be extended to the next stage before the first numerical digit has been dialled. All outlets busy, no overflow or alternative route. An overflow or alternative route , is marked over bank FMS5 and in its absence, the group selector is driven to the last contacts of the dotted banks whereupon TA, LC pull up in series but TD remains inert since its windings are now in opposition. LC connects up busy tone from BS, Fig. 2, and when the calling party clears, the relapse of A restores all apparatus to normal. All outlets busy, overflow routing. The group selector continues to rotate until an idle overflow outlet in a group marked over FMS5 is reached, whereupon TB pulls up, releases the latch magnet, and operates TO (1) which locks up over winding (ii), Fig. 2, to prevent its release when TO(i) is shortcircuited by ground reverted from the next stage. Switching relay H does not now operate so that further digits come in to A, Fig. 2. If all overflow outlets are busy, tone is sent back as in the preceding paragraph. The overflow outlets lead to switches such as SJL, Fig. 3, and as this switch may not be set before the first numerical digit is dialled, this digit is always taken by AS, Fig. 2, which has been stepped to position 13. The reception of this digit, the transference of the exchange code and first numerical digit from the first group selector control circuit FCC to the second selector control circuit SCC, Figs. 4 and 5, and the reception of the remainder of the numerical digits in SCC are overlapping operations but will be described in the order set out above. The first numerical digit,is repeated by A to ASDM either over contacts of E, F, G or directly over a contact of TO when this relay has operated. AS is now in one of positions 14-23 and when C relapses at the end of the train it cannot again re-operate. When switch AS was originally set by the A-digit, neither, one, or a combination of relays W, X, Y became operated over AS4 according to the setting, and the operated relay or relays locked up when C relapsed at the end of the train. When TO operates at the finding of an overflow outlet, interrupter M1, Fig. 2, continuously steps magnet SSDM of a sending switch. In position 1 of SS, SZ pulls up over SS3, locks, and connects interrupter M2 to the negative speaking wire. When SS2 reaches a position determined by the conditions of storage relays W, X, Y, a circuit is completed for windings (ii) of relays SZ and G which oppose windings (i) of these relays to effect their release. SZ terminates impulse transmission from M2, and G releases TM(ii) and transfers sending control from relays W, X, Y to wiper BS7. Sender SS proceeds to positio