THE MERCURY ARC AS AN ACTINIC STROBOSCOPIC LIGHT SOURCE

Abstract

Stroboscopic light sources capable of producing sufficient actinic light to take a photograph with a single flash are described in this paper. The duration of the main flash is of the order of 10⁻⁵ seconds, depending upon the circuit arrangement and the temperature of the light‐pulse tube. The light has been very useful for obtaining stroboscopic motion pictures of the hunting of synchronous motors, the surges of gasoline‐engine valve springs, vibrations of mechanisms, etc. Also, motion pictures have been taken upon continuously‐moving film at a rate of 480 pictures a second with a camera which has neither a shutter nor an intermittent motion. (Recently the speed has been increased to 4200 pictures per second.) The fundamental idea is to discharge considerable electrical energy into a mercury‐arc tube by means of an electrical transient, which is usually obtained from a condenser discharge. The gaseous discharge is capable of giving a flash of very short duration of high instantaneous intensity. Several methods of actuating the flash are described.