28,362. Siemens Bros. & Co., [Siemens & Halske Akt.-Ges.]. Dec. 4. Semi - automatic exchange systems.-In a system in which there are a number of selectors at the exchange for a larger number of subscribers, a calling subscriber is connected automatically to an idle selector on the panel of a disengaged clerk, and the selector is moved step by step till its contact arms reach the calling-leads. The first operation of the operating electro-magnet of a selector disconnects it from the calling-lead common to the group of subscribers, and connects the lead to a line leading to the next selector. When a call is made through a selector, a circuit is closed which renders busy all the selectors on the same panel until the clerk has enquired and made the necessary connexion. When .the subscriber T takes down his receiver, the call relay AR attracts its armature k, and a circuit of the operating-magnet H of the first disengaged selector is closed from the battery B over the armature k, lead d, armature e, and contact f. The armature g of the magnet H moves the selector round one step, thus moving also the cam x and breaking the contact at f. The contact n being now closed, any further call on the common lead d is passed on by the lead d' to the next selector. The further movement of the selector is obtained from the circuit of the battery B' over the armature g and contact m, the armature g acting as an interrupter. When the arm c' reaches the required selector contact, the circuit from the battery B over armature k, lead c, arm c', and magnet S causes the magnet to attract its armature i and stop the movement of the selector. The magnet also brings the arms a', b<1> to the required contacts. Current now flows from the battery B<3>, over relay SR', arm a<1>, through the subscribers' instruments, and over the winding wb of the call relay, to earth. The attraction of the armature h of the relav SR<1> closes the circuit of the call lamp AL, and also closes a circuit from the battery B<3> over the magnet S to keep the selector in position. The circuit of the call lamp AL passes over the relay AC, the armature c of which completes the circuit to earth of the relay BR. There may be a relay BR for each selector on the panel ; or the one relay may operate all the armatures e to cut off all the selectors of the panel from further calls. After enquiry, the clerk, by lifting the connecting-plug VS, opens the switch Sa and closes switches Sb, Sc. The panel is now open for further calls, and the circuits of the ring-off lamps SL<1>, SL' are completed. When the subscribers have hung up their instruments and the plug has been withdrawn, the magnet S is de-energized and the selector moves on to its initial position.