9233. Snook, H. C., and Kelly, E. W. July 3, 1914, [Convention date]. Vacuum tubes.-A R÷ntgen-ray or other tube is provided with means for introducing and means for withdrawing gas, these means working either continuously during the use of the tube or only when required in consequence of change of vacuum; they may be adjusted so as to maintain any required degree of vacuum. In one arrangement, there are provided two tubes 22, 28, Fig. 1, permeable to gas when heated. Platinum is preferred for the inlet tube 22, and palladium for the outlet tube 28. Each permeable tube is sealed through the junction of a separate bulb 21 or 29 with a common bulb 19 open to the main bulb B of the discharge tube, and is closed at its outer and open at its inner end. Heating is effected by current passed along the permeable tube, or by sparking between the tube and a platinumtipped anode near its closed end; in the latter case, the end of the tube may be thickened or protected by a small coil of wire, preferably of platinum. One of the separate bulbs 21 contains a gas such as hydrogen, argon, helium, neon, or xenon, or a mixture, preferably at a pressure much higher than that in the main bulb. The other separate bulb 29 may be open to the atmosphere or may be exhausted, or contain a gas other than that in the first bulb 21, so that when the tube 28 within the second bulb is hot, gas diffuses through it from the main bulb. In another arrangement, a single permeable tube 22<a>, Fig. 12, serves both for outlet and for inlet, its bulb 29<a> being open to the atmosphere but provided with means for generating hydrogen or other gas. As shown, a small tube b fitted into the bulb 29<a> by means of a cork ring is closed at its outer end by a cork or like stopper c, and at its inner end by a porcelain or other porous stopper f. Wires pass through both stoppers, the space between which is filled with water, alcohol, mineral oil, or other source of hydrogen or other gas. When water is used, the electrolytic gas passes through the porous stopper; when oil is used, the wires through the stoppers are joined, and the oil is carried through the porous stopper and decomposed by heat. In order to remove gas from the main bulb, the wires through the stoppers are disconnected from the source of current, and sparks are passed between the permeable tube and a terminal 26<a>. Instead of the small tube b there may be provided a porcelain or other porous non-conducting cylinder with a conductor wound about its outer end, and a wide recess at its inner end to receive the permeable tube; the plug is saturated with oil or hydrocarbon. The action of the gas admitting and removing devices may be controlled by hand or automatically. Fig. 3 shows each permeable tube connected to a terminal ring, into which may be hooked the end of a conductor 47 attached to a contact 42. Each main lead to the discharge tube comprises a curved arm 39 which may be swung by a pulley or cord so as to engage either with a contact 40 connected to the main terminal or with the contact 42. Preferably, the negative conductor is thus connected to the permeable tubes, while the spark terminals 26, 26' are connected together over a spark-gap 34, 35, and one of them is directly connected to the cathode terminal of the discharge tube. Instead of the conductor 47 to one of the permeable tubes, there may be provided conductors leading from both tubes to two terminals of a switch, the arm of which is mounted under contact 42 and actuated by a cord and opposing spring. In another circuit arrangement, the currents for heating the permeable tubes by resistance or sparking are obtained from the well-insulated secondaries s<1>, s<2>, Fig. 5, of transformers. An arm 55 is moved by hand over contacts of resistances r', r<2> to send a regulated current to the primary of either transformer. If the resistances r<1>, r<2> are replaced by a single one, current may be sent continuously to both permeable tubes so that gas is simultaneously admitted to and removed from the discharge tube, the rates of these actions being' regulated to vary the vacuum. The two transformers referred to may be replaced by a single one, regulation being effected in the secondary circuit by a switch arm connecting adjacent ends of the permeable tubes to a variable point on a resistance. Current for the main discharge terminals may be supplied through a transformer T and synchronous rectifier F by a motor-generator or inverted rotary converter G, from which the heating-current is also obtained. In one form of automatic vacuum regulator, the resistances r<1>, r<2> are replaced by adjustable contacts at opposite sides of a switch arm operated by an electro-magnet in shunt to the primary of the main transformer T, the pressure across which rises with increase of vacuum in the discharge tube. A spring opposing the electro-magnet may be connected to a tension-adjusting handle bearing an index moving over a scale, which may be graduated in terms of degrees of hardness or lengths of equivalent spark-gap. In other automatic regulators, an electrostatic switch is used. Fig. 9 shows plates 81, 82 connected together by a light flexible conductor. One of the plates is stationary and is connected to a main terminal of the discharge tube. The other plate 81 is carried by a pivoted arm 74, in which are adjustable screws 78, 79 separated by spark-gaps from the sparking-terminals of the gas bulbs. These gaps are in parallel with an adjustable spark-gap 72, 73 in one main conductor, and the lengths of the gaps are such that, when the pivoted arm 74 is in normal position, no current reaches either permeable tube. The arm 74 is under the control of an adjustable counterweight 84 and a tensionspring 76, the outer end of which is attached to a pointer capable of being clamped at any desired position on a scale. This arrangement may be modified so as to work by electrostatic attraction instead of repulsion, an insulating- screen being placed between the charged plates. Another modification consists in connecting the permeable tubes and their sparking-terminals in series in one of the main leads of the discharge tube, and in shunt to a resistance. An arm actuated by the electrostatic means described, or by a quadrant electrometer, is connected to the conductor between one permeable tube and the sparking-terminal of the other tube, and has at one end a terminal travelling over a path close to the resistance, so as to adjust the proportions of current taken by the two heating spark-gaps. In a further modification, the terminal on the arm moves near a curved bar providing a direct path to the main electrode, and, at the ends of its range of motion, comes close to or into contact with terminals connected to the heating spark-gaps, which are thus placed in shunt to the gap between the arm and bar. These terminals are adjustable along a scale. Cooling-means for a R÷ntgen-ray tube are also shown in Fig. 1. Each electrode A, C is mounted on a tubular stem 5 or 11 of copper or the like, which is welded, brazed, soldered, or otherwise secured to a platinum tube 6 or 12 sealed into the container. In the anode platinum tube 6 is a corrugation 6<a> to allow for thermal expansion. The anode A is also supported by a metal tube 2 fitting over a glass tube fused to the envelope. A tube 7 or 11 for the supply of air or other cooling-fluid traverses the tubular stem of each electrode. The anode air-tube 7 is attached to a perforated cap 10 fitting on to the envelope, and the cathode air-tube to a cap 14 on a sheath 15 secured around the cathode tubulure by a ribbed cork or like ring 16 and preferably terminating in a bell 18. More than half the surface of the container is thus cooled by air escaping from the cathode stem.