STROBOSCOPE. An instrument used for studying the motion of a body where by means of a rapid succession of slits or other openings, or its illumination at regular intervals, the eye receives a series of images on the retina. Where these impressions occur with sufficient rapidity the illusion of motion is produced, and advan tage of this is taken in certain toys and scientific instruments. In its simplest form the strobo scope, which was first devised by Stampfer and Plateau, consists of a disk or cylinder with a series of slits through which the observer looks at the pictures or moving object. As the disk or cylinder revolves the slits conic successively before the eye and through them the observer gets a series of glimpses of the moving object. If each of the pictures represents a successive stage in an action such as the motion of a pendulum, a man or animal running, etc., the illusion of motion is produced, provided that the interval between the glimpses of the pictures is less than the duration of the image on the retina a time, which varies from 1-10 to 1-50 of a second. A simple stroboscope or zoetrope is
illustrated in the article It.ursioN, while under KINETOSCOPE will be found descriptions of some of the more complex apparatus based on this principle. Anschiitz (q.v.), a German photog rapher, who had achieved considerable success at instantaneous photography, made an important application of the stroboscope principle in his "tachyscope," by rotating transparent pictures on a drum or disk, and having them illuminated by the momentary glow produced by the passage of a spark from an induction coil through a Geissler tube. Although the period of discharge is very brief, yet the sparks follow with reg ularity, and as the successive pictures always occupy the same position relative to the eye of the observer, the illumination appears continu ous. and the effect of motion is produced. See ILLUSION: KINETOSCOPE.