Mercury Lamp, by Kelvin Bottomley & Baird Ltd., London, 1924

The cast iron triangular shaped base supports an iron pillar that carries by adjustable collars the lamp and its shade. The lamp is a tube which contains mercury between a pair of electrodes. When an electric discharge is struck in the mercury vapour an intense source of ultraviolet and blue light is obtained. The shade is a sheet tin box with a hole to view the light. Around the back runs a black velvet curtain.