413,442. Automatic exchange systems. ERICSSON TELEPHONES, Ltd., 67, Kingsway, London, and DRYSDALE, L. H., c /o Ericsson Telephone Works, Beeston, Nottingham. March 28, 1933, No. 9336. [Class 40 (iv).] Connections between subscribers on different automatic exchanges on an omnibus junction are effected without the intervention of an operator by dialling first a digit (9) to seize the junction if idle and then a further digit (1 to 4) corresponding to the position of the wanted exchange on the junction as seen from one end (at which the junction may be connected to a main manual exchange). The impulses of the second digit are transmitted over one leg of the junction to the mainexchange end and are then repeated back over the other leg each impulse being effective in extending the connection from one exchange to the next. Subsequent trains of impulses corresponding to the wanted subscriber's number are then transmitted in the same way if the called exchange is nearer to the main exchange than the calling exchange, or directly to the called exchange if this is more remote. The exchanges may be merely switching points at which branch lines are connected and such a branch line may also be an omnibus junction. The reception and retransmission of impulses at the main-exchange may be effected by a register with or without translation. In the system described, four exchanges A-D characterised respectively by digits 1-4 are provided each having a capacity of eighty lines and each having detailed circuits as shown in Figs. 2 and 3 with the exception that at exchange D terminal 1, Fig. 3, is connected to earth and terminals 2 and 3 are strapped together. A modification is referred to in which each exchange is of 100-line capacity and an additional prefatory digit is employed to signify a local call. Local call. Local calls are established in substantially known manner over the first eight levels of the final selector R, Fig. 2. Call from one automatic exchange B to another. In. response to the digit 9 post springs NP of the local final selector operate energizing relay CL which connects the lower winding of relay OB to conductor 11. If the omnibus junction is free, OB operates energizing CO over lead 12. Relays L in exchanges B and A are now operated from battery over resistance 15 in series with relay LA at the main exchange, Fig. 5, and relay L of exchange B also completes a circuit over conductor 17 for relays L in C and D. In each automatic exchange L operates BC to busy the junction, and at the manual exchange BD operates to busy the sleeve of jack J. In the calling exchange B, relay GA interacts with magnet DM to associate a finder WA with the calling circuit and relay K then operates connecting battery over resistance 8 and contacts a2 to the upper junction conductor in place of resistance 15. Relay D operates in this circuit and causes 0, OA to operate. Impulses of the next digit are therefore repeated by relay A over the upper conductor to relay LA instead of to rotary magnet R. During the digit relays CC, ON operate in each automatic exchange and CCA ONA in the main exchange. The first impulse is repeated back over the lower junction conductor 25 by relay LA and energizes relays T, W, in exchange A. At the end of the impulse, relay X operates in series with W connecting T in series with the lower junction conductor. The second impulse thus operates T in exchanges A and B ; at A relays Y and Z successively operate short-circuiting T to prevent response to any further impulses, whilst at B relays W and X operate as in exchange A at the first impulse. At the end of the digit, in the wanted exchange relays W and X but not Y and Z will be operated and on the relapse of CC, relay BA operates completing a circuit for steering relay CA of the incoming final selector RA, Fig. 3. The two remaining digits of the subscriber's number are then repeated by relay A (in B) and L (in the called exchange) to the vertical and rotary magnets VA, RA, these digits passing directly over conductor 17, owing to the operation of relay XF (in B), if the called exchange is more remote. If the junction is busy when digit 9 is dialled, relay OB does not operate and relay G energizes on the relapse of C to connect up busy tone. If the subscriber dials the number of his own exchange, BA does not operate owing to the operation of CO and NU tone is connected up. NU tone is also transmitted over strap 2, 3 at exchange D if a second digit greater than the number of exchanges is dialled. Call to main exchange. When digit O is dialled, springs NP after operating relay CL are restored connecting battery over conductor 22 and the lower junction conductor to energize relays IB, OP. The latter energizes SY to light calling lamp LP. When a plug is inserted, relay S operates, and the call is extended manually. When the calling subscriber hangs up, relays LA, BD, release, and if the plug is not taken down, relay BB operates connecting battery over resistance 29 to the upper junction conductor to re-energize the line and guard relays at all the automatic exchanges. Call from main exchange. When a calling plug is inserted, relays S, BB, operate, completing a circuit over relay LA for relays L in all exchanges, and by the throwing of key DK impulses from dial IC are repeated by relay LA over conductor 25 in a manner similar to that for a call from one automatic exchange to another.