The Educational screen (c1922-c1956])

April, J 93 2 Page 125 AMONG THE PRODUCERS Where the commercial fir mi — whose activities have an important bearing on progress in the visual field — art free to tell their story in their own words. The Educational Screen is glad to reprint here, within nec- essary space limitations, such material as seems to have most informational and news value to our readers. The Franklin Institute Eclipse Projector LOUIS WALTON SIPLEY A VISUAL aid for showing eclipses of the sun has been developed by James Stokley, associ- ate director of the Franklin Institute of Philadel- phia. The unit consists of a device invented by Mr. Stokley for projecting images on a translucent n. The construction of the device permits continuous reproduction on the screen of three types of eclipses, < 1) partial, (2) annular and (3) total. In Figure 1 is shown the device with cover re- moved. This consists of three projectors, A, B, and (', mounted side by side. Illumination in each projector is by a 500 watt incandescent lamp. Pro- jector A is used to project a circle of light through the screen, representing the sun, and is fitted with a circular disc, D, on which are mounted circular rubber discs E. When in operation the disc, D, revolves and the rubber discs, E, pass before the ray of light from the lamp, throwing a shadow on the screen. The size of the rubber discs vary and Figure 1 being placed in different positions produce different screen effects. In the partial eclipse one of the rub- lie r discs produces a shadow which is preceded and followed by a crescent of light as it moves across the screen. In the annular eclipse the moon's shadow moves across the sun until only a circle of light remains on the screen. Both the partial and annular eclipses are pro- duced by means of projector A. The most interest- ing eclipse, total eclipse, is represented through the use of all three projectors. Figure 2 shows the suc- cessive stages of this eclipse as represented on the Figure 2 screen. At stage 1 the moon is moving across the face of the sun. This is accomplished by means of projector A. When the shadow has fully covered the sun projector C is automatically turned on and by a perforated slide, G, the Bailey's Beads effect is produced as shown at stage 2. This represents the sun rays flashing through the valleys on the moon's surface. This is instantly followed by the corona effect, stage 3, and which is accomplished by projector B moving into action with a special colored slide, H. The result here is very beautiful, the brilliant flames and great bands of light show- ing around the dark shadow of the moon. As the moon starts to move away the Bailey's Beads ap- pear at the right, stage 4, and then the crescent of 1'ght grows until the full sun is again depicted. The projector device was made by Bausch & Lomb Optical Company of Rochester to Mr. Stok- ley's design and specifications. The construction of the complete unit required great care and ac- curacy. The special slide for the corona was made by C. W. Briggs Company. The moon disc on the slide had to measure exactly 1.385 inches and the coloring was made to Mr. Stokley's specifications. This eclipse projector is the only one of its kind in the world and will be used in the new Museum of Franklin Institute where it will be kept in con- tinuous operation when the Museum is open to the