324,675. Standard Telephones & Cables, Ltd., (Western Electric Co., Inc.). Oct. 31, 1928. Automatic exchange systems.-In registercontroller systems of the reverting impulse type, the impulses comprise successive reversals of current over the fundamental circuit, the reversals being effected by commutators associated with the selecting switches. The stepping relay in the register-controller may be polarized so that only alternate impulses are repeated to the counting device, the connections to the stepping relay being reversed when the digit is odd, so that an extra reverting impulse is required to effect the saturation of the counting device. The invention is described in connection with a paneltype final selector, Fig. 3, reached over a group selector, Fig. 2, and district selector, Fig. 1. Final selector, Fig. 3. When the connection has been extended to the final selector, sequence switch 200, Fig. 2, is in position 7, the sequence switch of the district selector being in position 10. The fundamental circuit extends from battery over 304, 318 (ii), 303, 302, commutator brushes 301 and 306, 305, b-wire, 214, 213, 212, 210, to the polarized stepping relay 115 and a further polarized relay 124, and returns over relay 206, Fig. 2, and the a-wire, commutator brushes 308, 311, to ground over 313. Relays 318, 206 energize and slow-release relay 217 pulls up to lock relay 201 until the final selector has been set. The direction of the current flow over relay 115 is controlled by relav 117 connected to odd terminals in a bank 113 of the hundreds register, and it will be assumed that the hundreds digit is even and that relay 115 energizes over the fundamental. Relay 318 energizes 314 which locks and completes a circuit for moving sequence switch 300 to position 2. The original circuit of relay 318 is opened at 303 but a holding circuit now extends over 324, 303. The up-drive magnet 325 moves the switch-shaft for brush selection and at the first and each alternate brushchoosing position, commutator brushes 306, 308 engage the strips 310. 307 instead of the strips 307, 309 respectively so that the current over the fundamental is reversed, the commutator brushes being of the bridging type to prevent opening of the fundamental. The original energization of stepping relay 115.connected ground over wiper 114 of the hundreds register to one of the lower row of counting relays, say relay 127. This relay locks in a circuit including relay 126 which, however, is short-circuited by relay 115. At the first reversal of current, relay 115, being polarized, falls back, 126 pulls up and extends the original operating circuit of 127 to 129. When the current over the fundamental is restored to its original direction, 129 energizes and at the next reversal 128 and 118 operate in parallel, the register distributor switch represented by wiper 110 being advanced, in known manner, to connect up the tens register and the counting relays released. Relay 118 opens the fundamental circuit and relay 318 falls back to open the circuit of the up-drive magnet and complete a circuit for driving switch 300 to position 3 in which the brush-tripping mechanism is energized and the fundamental circuit is again closed. It will be assumed that the tens digit is odd and therefore relay 117 is energized over a bank of the tens register similar to that of wiper 113 of the hundreds register. The fundamental circuit now extends from battery over 304, 318 (ii), 903, commutator brushes 323, 331 and the previously traced circuit except that the current flow over 115 has been reversed by relay 117, the return circuit extending from a-wire over commutator brushes 322, 335 to ground over 313. Relays 318, 206 pull up as before, but both 115 and 124 remain de-energized. Relay 318 closes a circuit for driving 300 to position 4 and energizes the up-drive magnet 325. As the first group position is approached, brushes 331,322 leave strips 330, 333 and engage strips 334, 330 respectively so that the current over the fundamental is reversed and stepping relay 115 energizes one of the counting relays over cam 130 (position 11) and the tens register (not shown). Upon each energization and de-energization of relay 115 following reversals of current during group selection, a pair of counting relays is operated as described above and when relays 128, 118 pull up the register sequence switch is advanced, the counting relays are restored and the fundamental is opened. Relay 318 falls back to open the circuit of the up-drive magnet and close a circuit for driving 300 to position 5 in which the fundamental circuit is established over commutator brushes 308, 301, 306, 311 as in the case of the hundreds digit, the brushes 306, 308 being engaged with segments similar to 336, 337 immediately beneath the selected tens group. Relay 318 operates, sequence switch 300 moves to position 6 and the slow speed up-drive magnet 338 energizes. The final selector is set in accordance with the units digit in the manner previously described and relays 128, 118 operate to restore the counting relays and open the fundamental. Relay 318 falls back and sequence switch 300 advances to position 9, the magnet 338 being de-energized. The fundamental has remained open sufficiently long for relay 217, which is dependent on relay 206, to relapse, and relay 201 thereupon releases and sequence switch 200 advances to position 9 in which battery over relay 201 (ii) and ground over cams 220, 221 are connected to conductors 210, 209 to operate relay 124, Fig. 1, which in known manner causes the district selector to move into the talking position, On reaching position 9, sequence switch 300 closes a circuit for 318 (ii) which locks up until the switch leaves position 10 and closes a circuit for driving 300 (i) being completed in position 10. In over 318 (i) being completed in position 10. In position 11, the test circuit [321, 302, 303, 318 (ii), 324, 339, 341] is completed.. If the called line is free, relay 318 falls back and completes a circuit for driving 300 to position 13 and thence to positions 14 and 15. The wanted subscriber is rung and the connection completed in known manner.