762,681. Automatic exchange systems. SIEMENS BROS. & CO., Ltd. Feb. 25, 1955 [Dec. 24, 1953], No. 35861/53. Class 40 (4). [Also in Group XL (a)] A gas-filled multi-gap cold cathode electric discharge tube has main anode and cathode electrodes one of which electrodes is in the form of a helix and the other of which is of linear form lying parallel with the axis of the helix and spaced therefrom to form discharge gaps with the helix, and guide electrodes arranged to provide discharge gaps with one of said main electrodes to cause a discharge between the main electrodes to move along the helical electrode in response to pulses applied to the guide electrodes. The tube may serve for the storage and subsequent utilization of a number of successively dialled digits in a telephone exchange switching system. Fig. 6 shows diagrammatically a tube capable of operating as a four-digit counter and comprising a counting part and a distributer part. The counting part comprises the portion of a helical main cathode 7 commencing with the 5th turn which is designated 71, a separate single turn output cathode 8, and a home turn 10 separated from the output cathode 8 but connected internally or externally with the main cathode 7, and two guide electrodes 5 and 6 wound between the turns of the cathodes in the manner of a three-start screw thread. Five rod anodes 41 to 45 are spaced around the cathode electrodes and extend for different distances along the tube, terminating respectively opposite the 5th, 4th, 3rd, 2nd and 1st turn of the main cathode 7. The distributer part of the tube comprises the first four turns of the main cathode 7, two distributer guide electrodes 13 and 14 which are separate from the guide electrodes 5 and 6, and a priming cathode 11 having fingers 12 extending for different lengths to form priming gaps with the ends of the several anodes. The tube is connected in a circuit, Fig. 7, wherein the anodes 41 to 45 are connected over resistances such as R41 to a source of positive potential main cathode 7 is connected to earth, output cathode 8 is connected over resistance R<SP>4</SP> to earth and over condenser C<SP>3</SP> and wire UC to a utilization circuit and priming cathode 11 is connected over condenser C4 to wire NP to which negative pulses may be applied and also over resistance R<SP>11</SP> to earth. The guide electrodes 5 and 6 are connected to a device IS which applies successive pulses of opposite polarities to the guide electrodes in response to each impulse received over wire IMP, and may be switched to a source LS of locally generated impulses. The distributer guide electrodes 13 and 14 are connected to a device ED which generates successive positive and negative pulses at the end of each impulse train received by it over wire IMP. When the tube is taken into use a negative priming pulse is fed over wire NP to the priming cathode 11 and discharges are set up between this cathode and the end of each anode. When the priming pulse terminates these discharges transfer to the turns of the main cathode 7 adjacent the ends of the respective anodes, the discharge on anode 41 appearing on cathode turn 71 and the discharges on the other anodes appearing on cathode turns 4, 3, 2 and 1. The first impulse train to be counted is transmitted over wire IMP to the. device IS which delivers successive positive and negative pulses at each received impulse to the guide electrodes 5 and 6 to cause the discharge on anode 41 to advance along the counting part of the tube. At the end of the impulse train successive positive and negative pulses are transmitted from the device ED to the distributer guide electrodes 13 and 14 to cause the discharges on the first four cathode turns to advance one turn so that the discharge on anode 42 now appears on cathode turn 71. The impulses of the second impulse train give rise to pulses on guide electrodes 5 and 6 to advance the first and second discharges between their respective anodes and the turns of cathode 7 so that the spacing between the first and second discharges corresponds to the number of pulses in the first received impulse train. At the end of the impulse train device ED again advances the discharges in the distributer part of the tube by one turn. Successive impulse trains are counted in a similar manner and at the end of the fourth train there will be spaced discharges between the cathode 7 and anodes 41 to 44 and a discharge between cathode turn 71 and anode 45. For the utilization of the counted impulses, pulses from the device LS are delivered to the guide electrodes 5 and 6 and at the same time to the utilization circuit connected to the output cathode 8. The discharges are advanced along the tube towards the output cathode 8 where they give rise to a signal over the wire UC to indicate that counting of a digit is to cease and counting of the next digit is to commence. Discharges appearing on the output cathode 8 are transferred by the action of the guide electrodes to the home turn 10 where, by reason of a direct connection to earth of this turn, a plurality of discharges to the several anodes may be sustained. When the last digit has been counted out, the tube is extinguished. In an alternative arrangement the distributer part of the tube is replaced by an external electronic distributer of any known form. Simplified arrangements are described including a tube having helical cathode and guide electrodes with only one rod anode and a tube having a helical cathode around which are spaced a single rod anode and two rod guide electrodes or alternatively a helical anode around which are spaced a rod cathode and two rod guide electrodes. In these arrangements digits are counted out by applying pulses to the guide electrodes in reverse order.