Illumination notes

A Midget Sun. A 1,000-watt mercury-vapor lamp, no bigger than a cigarette, with an intrinsic brilliancy about one-fifth of the sun´s, is now available. The lamp itself is a capillary quartz tube containing electrodes, a drop of mercury, and a little argon gas for starting. The heat and pressure are such that water-cooling is necessary, so an outer tube is provided as a water jacket about the size of a shotgun cartridge. The light is much whiter than that of the well-known low-pressure mercury-vapor lamp. If the outer tube is made of quartz instead of hard glass, the lamp is a powerful source of ultraviolet radiation. The efficiency is about three times that of an incandescent lamp of corresponding wattage. Suggested uses are in projection, photographic processes, and therapy.