257,310. Siemens Bros. &. Co., Ltd., and Humphries, H. E. April 25, 1925. Antomatic and semi-automatic exchange systems.-In a system in which a connection is set up under control of an operator over automatic switches at a distant exchange, a position lamp lights when each selector switches through to indicate that the next digit may be dialled. The interexchange trunk terminates in a first selector having feed bridges, the line relay of which has a high-resistance winding A(2), Fig. 1. which is effective during impulsing, and a low-resistance winding A(l) which is connected up by a relay RB energized in series with the line relay of each succeeding switch as it is seized. These windings are connected in parallel over the b-wire of the trunk to a marginal relay J which controls a lamp JL. First selector, Fig. 1. When the operator plugs into the jack 2. relay J energizes in series with line relay A(1) over the b-wire, and lights lamp JL. Relays V. D energize and a dialling signal DS is sent back. Relay RB operates without effect. Relay A repeats dialled impulses to the vertical magnet VM at back contact a1 and at the first impulse, relay L energizes and locks. Dialling relay D is held at back contact a2, and falls back at the end of the train, connecting up the rotary maguet RM, and releasing relay BB, which substitutes high resistance winding A(2) for low-resistance winding A(1), so that relay J relapses, and lamp JL is extinguished. Relay J is prevented from releasing between impulses by a winding which is short-circuited by the dial ofe-normal springs dl1. When an idle second selector is found, test relay T operates and extends the connection thereto. If all the outgoing links are busy, relay T operates over the 11th terminal, and a busy signal is sent back. Second selector, Fig. 2. Line relay AA energizes over the b-wire in series with relay RB, which replaces low-resistance winding A (1) to light lamp JL: Dialling relay DA energizes. Impulses are repeated by relay A at contact a3 and by relay AA at contact aa2 to the vertical magnet VM, and relay N energizes at the first impulse over the test wire, being no longer shortcircuited at contact k1 and locks. Relay DA falls back at the end of the train, connecting up the rotary magnet RM and disconnecting line relay AA, so that relay RB relapses, and lamp JL is extinguished. Test relay TA extends the connection when an idle connector is found. A busy signal is sent as before if all the outgoing links are busy. Connector, Fig. 3. Relay NA (1) energizes over the test wire, end line relay AB over the b-wire, connecting up dialling relay DB. Relay RB operates as above to light lamp JL. Impulses are repeated to the vertical magnet VM at contact ab1. Relay DB falls back at the end of the train, and connects up change-over relay G, which closes a fresh circuit for relav DB. The pause imposed at the dial is sufficient for changeover, so that no signal is necessary. The last train of impulses are repeated to the rotary magnet RM, and relays DB, G then fall back in turn, test relay TB being connected to the. test wiper in the interval. If the wanted line is idle, relay T B energizes, and ringing relay S operates when relay G falls back. Ring cutoff relay TR (i) energizes when the called party replies, and short-circuits relay S at contact tr1. Answering relay Y energizes over the a wire. and sends back a signal over the a wire to the operator's position. The called party is fed with current over relay RB. If the wanted line is busy. test relav TB does not operate, and when relay G falls back, ring cut-off relay TR (2) energizes and sends back a busy signal at contact tr2. Modification. The Provisional Specification states that, at a selector without feed bridges, the line relay may be connected up over a vertical off-normal contact, or a contact of a relay controlled by the dialling relay.