371,673. Discharge lamps. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London.-(Assignees of Found, C. G. ; 1190, Phoenix Avenue, Hull, A. W.; 1435, Lowell Road, and Smith, J. C. ; 11, South Church Street, all in Schenectady, New York, U.S.A.) June 22, 1931, No. 18020. Convention date, June 24, 1930. [Class 39 (i):] A discharge lamp is supplied with alternating current of sufficiently high frequency to produce continuous luminosity and variation in the intensity of the light is obtained by varying the duration of successive waves of current. This may be done by varying a negative electrostatic field surrounding the positive electrode. The Figure shows a circuit for controlling the light emitted from a lamp 1 containing neon, helium, carbon dioxide or mercury vapour &c. The lamp is provided with a thermionic cathode consisting of a heater 5 within an electron-emitting shell 4 coated with alkaline earth oxides or rare metal &c. The heater is connected at one end to a conductor 6 and at the other end to the shell 4 which is provided with a leading-in conductor 7. The heater is fed from a transformer 8 the primary of which is connected to tappings on a main transformer 11. The lamp has two anodes 2, 3 of graphite, nickel, iron, tungsten, &c. connected through resistances 15, 16 to the terminals of the transformer 11. The anodes are surrounded by grids 17, 18 of wire gauze or perforated sheet metal. The grids are connected by conductors 19, 20 to the secondary of a transformer 21 the primary of which is connected by conductors 22, 23 to the alternating supply lines 24, 25. In the conductor 23 is a capacity 26 shunted by an adjustable resistance 27. By varying this resistance the phase of the current in the primary of the transformer 21 may be shifted with respect to the phase of the current supplied to the anodes 2, 3. Connected to the cathode 4 is a conductor 28 including a hand-operated switch 29 and a mercury switch 30 which is tilted by the armature 32 of a solenoid 31. A circuit through the mercury switch from the transformer 11 is completed by a conductor 34 containing a resistance 35 connected to the conductor 13. The lamp contains an auxiliary electrode 36 connected to the mid-point of the transformer 21 and by a conductor 37 and resistance 38 to the positive terminal of a direct current source, the negative of which is connected by a conductor 39 to the cathode 4. During the operation of the lamp a small discharge is maintained continuously between the cathode 4 and electrode 36. To start the lamp the switch 29 is closed whereupon a current flows from the conductor 28 to the conductor 13 through the solenoid 31 and switch 30. The latter thereupon tilts, breaks the circuit and impresses a high voltage on the lamp. The negatively charged grids surrounding the anodes prevent flow of current to the active anode until the negative potential on the grid has attained a critical value. The lamp then lights until the grid again becomes sufficiently negative to stop flow of current. The length of time in each cycle during which the lamp is alight depends upon the phase relationship between the anode and grid potentials and this is varied by the resistance 27. Due to persistence of vision the lamp appears to be alight continuously. The small amount of ionization produced by the current flowing to the electrode 36 facilitates the operation of the lamp. Specification 223,921, [Class 39 (i), Electric lamps, Arc. &c.], is referred to.