Stroboscopic and Slow-Motion Moving Pictures by Means of Intermittent Light--

In a paper published in the June issue of the Journal the author showed that mercury-arc lamps when excited by quick violent electrical transients make a practical source of intermittent light which is very actinic and has a short duration of flash. The timing of the flashes is easily controlled. - In this present paper, further information regarding the duration and the quality of the light are given. Also improvements upon the mercury-arc tubes are described which simplify the construction of the light-pulse tube and the electrical circuits. - Uses of intermittent light for taking motion pictures are described and illustrated by examples. There are in general two methods of using the intermittent light. One method is used to take pictures where the light is caused to flash for each frame and the film runs at a continuous speed. The second is used to take stroboscopic moving pictures of rapidly moving objects by causing the light frequency to approach the frequency of the motion of the object. Examples of the later method are shown, these being stroboscopic motion pictures of a crude motion picture claw mechanism operating at 30 fps. and of the surges in the valve springs of a gasoline engine running at 1930 rpm.