472,539. Cathode-ray tubes. ZEITLINE, V., ZEITLINE, A., and KLIATCHKO, V. Feb. 21, 1936, Nos. 5304 and 5305. Convention dates, Feb. 22, 1935 and Jan. 18, 1936. [Class 39 (i)] In electron - optical systems for cathode-ray tubes, the modulating electrode extends around or beyond an accelerating electrode so that it affects a focusing field on the side of the accelerating electrode remote from the cathode as well as providing a modulating field near the cathode, the variations of this focusing field on variation of the modulation voltage compensating for the simultaneous focusing variations due to the modulating field and to the varying mutual repulsion of the electrons in the beam and so keeping the spot on the screen accurately focused and of invariable size during the modulation. The modulating electrode M, Fig. 1, controls the intensity of the beam from the cathode C and extends around the accelerating electrode A<1> to provide a variable focusing and retarding field between the electrode A<1> and an electrode L. This electrode L is connected to the electrode A<1> and co-operates with a high-voltage anode A<2>. To avoid damage to the cathode by highvoltage discharges, it is fixed in the electrode M by mica discs D', D<2> and is closed by an insulating plug I. Dimensions and voltages are specified. In a modification, Fig. 2 (not shown), the modulating electrode is a cylinder extending around anode diaphragms fed through resistances. The electron beam may be brought to a focus in apertures of the diaphragms and two diaphragms may be near together to produce a sudden refraction of the electron paths. In another modification, Fig. 3, the modulating electrode 3 is a cylinder of metal net closed by a diaphragm 10a and its field extends through a similarly formed anode 4. Higher voltage anodes are provided as shown at 6 and 9, the anode 6 being of metal net. In other modifications, the modulating electrode is in the form of a closed chamber surrounding an accelerating disc with end apertures or in the form of a large-apertured, large disc which extends beyond, and so varies the focusing field beyond, the succeeding anode disc. In a further modification, Fig. 7, the modulation electrode comprises interconnected curved grids 3a, 3b on opposite sides of anode grids 4, 6. The cathode 2 has a spherical surface emitting electrons radially. A second concentrating system 8, 8a is provided and a wall coating is divided into two or more parts 9a ... 9c. To increase the sensitivity of the electrostatic or magnetic deflection of the ray, the coating such as 9b around the point of deflection is maintained at a low potential. The coatings are so biassed that the deflected beam is not bent or the position of the spot on the fluorescent screen is not altered, for example, the equipotential surfaces are spheres with centres at the point of deflection. In another modification, Fig. 8 (not shown), the modulating electrode is formed on a precision lathe and is a cylinder with an end plate apertured to receive a needle - shaped cathode. Disc electrodes separated by thin glass or mica are mounted inside' the cylinder. In other modifications, the cathode is concave or hollow with its interior or bottom only activated and cooperates with an apertured anode disc and a modulating cylinder which has an apertured diaphragm near its end facing the cathode and which contains apertured diaphragm anodes. The Specification as open to inspection under Sect. 91 comprises also a cathode-ray tube in which negatively biassed concentrating cylinders are interposed between successive anode diaphragms. This subject-matter does not appear in the Specification as accepted.