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Types of Visual Aids and Their Uses 97
filming is a large one and, for those partieularly interested in it, there are a number of excellent volumes and sources of information. The Union Library catalog of Philadelphia and the catalog of the Special Libraries Association at New York City are among the best.
Microfilms may be made on 16 mm. or 35 mm. film stock. In 35 mm. film, both perforated and nonperforated types are available. The perforated 35 mm. film is regular motion-picture stock. Nonperforated film has the same overall size, but the sprocket holes are omitted, thereby allowing additional space to be covered with the photographed material. Microfilming apparatus is available from such companies as Eastman, Folmer Graflex, and others.
A microfilm reader, which is manufactured by the Society for Visual Education*, accommodates both perforated and nonperforated film. It will also accommodate 16 mm. microfilm, but it was not constructed for the express purpose of showing this size, and the magnification may not always be satisfactory. The magnification of the projector is from one to twelve. The unit has a 100-watt lamp, is easy to operate, and uses 100-foot reels. The film advancing and reversing mechanism is simple and efficient. The machine can be used in a fully lighted room because of its shadow-box arrangement over the reading surface. It is small, compact, and readily adaptable for use on a small table or an ordinary library desk or reading table.
Three Dimensional Projection
In the development of the use of films in education, it was first possible to have a projected image in black and white, and only in the past few years have we been able to obtain full natural-color projected images through the development of color film. Now, however, we are also able to have, in addition to color, the experience of depth in projected images. This is possible because of the introduction of a photographic and projection system for stereo films.
The stereo projection equipment is available in two designs — one for stereo filmstrips only and one for both filmstrips and stereo slides measuring 2" x 4*4". Stereo pictures consisting of two pictures of a single scene are mounted in pairs and are either placed between cover glasses measuring 2" x 41/4 ", or printed as pairs on 35 mm. filmstrips. The three dimensional effect is given through the use of Polaroid filters in the projector and the use of Polaroid viewers or spectacles by the
*Society for Visual Education, Inc., 100 East Ohio Street, Chicago, Illinois.