Educational screen & audio-visual guide (c1956-1971])

(Fif^tire 1) A Science student taps a hurned-out light bulb that has been inserted between the filmstrip projector barrel and lens. Tim simple demonstration affords the whole class an example of harmonic motion, from the projected image of the bulb's vibrating filament. these shadows can be observed. Using a bunsen burner they can be detected right up to the ceihng of the rcx)m. It is interesting to note that the candle flame actually casts a shadow against the wall, so bright is the projector beam in comparison to it. 6. Projecting constellation.^— Making constellations for projection is an interesting project for younger groups. Aluminum foil is first pressed around the barrel of the projector (with lens removed), determining the size of the field. The foil is flattened out (with a circular mark left on it from the rim of the barrel ) and a portion of a star chart with the desired constellation placed over the foil. Pins stuck through the chart and foil are used to mark the stars. The foil is carefully folded back over the barrel exactly as before and the lens projects the constellation. In order to take full advantage of the field of light issuing from the projector, we found that two 4" hand lenses work better than the regular projection lens, because they gather and project even the light issuing from pin-holes very close to the rim of the barrel. The loss in quality of the image is not apparent, since only points of light are projected. A ring stand and clamp to hold the lenses are helpful for long showings. 7. Detail in topographical nuips— In the absence of an opaque projector, detail in a topographical map can be projected in much the same way. The desired portion of the topographical map is placed over the open barrel of the projector and the lens held before it. Projection in this manner can be used for wall tracings. If the area is that which immediately surrounds the school, or the locale of a planned field trip, it might be a good idea to duplicate such detail by transfering the tracing to a master sheet and dittoing copies for students. (Maps of just about any area in the United States can be obtained from the Geological Survey in Washington, D. C. for 30 cents per map. ) 8. Source for concentrated light-bea7n— The filmstrip projector emits a beam of light which gradually spreads out. Without doctoring, this is not particularly useful in showing the refraction of light as it passes through a lens or prism. To get a concentrated beam of light for use in smoke box experiments on refraction, we set a one liter flask filled with water in front of the projector beam. The beam of light can be seen to narrow as it passes through the flask. This arrangement has also proven useful in concentrating the light from the projector in order to study tracks of radiated particles in a cloud chamber. While the filmstrip projector can be used in microprojection without concentrating the light, better results can be obtained if the projector lens is removed and the light projected through a water-filled flask. The light is then reflected by the microscope mirror, (using the flat side of the mirror) up through the specimen to be viewed, and through the microscope lens system. A sheet of paper held over the microscope and about a foot from the top, will show a fair-sized image of the specimen. A still stronger light beam can be obtained by removing the eye-piece of the microscope. This beam can then be projected onto a screen by placing a right-angle prism over the top of the microscope. (Figure 2) 9. 35m77i material— Home-made filmstrips can be made with direct-positive film or by printing the negatives onto 35mm fine-grain positive film. Such filmstrips are particularly good when a field trip is planned to some local point of interest. Close-ups of pot-holes in the rocks at the New York Botanical Gardens were made and students then were asked to locate these on the field trip. Tiros satellite film is available and can be projected directly also. When ordering such film it is necessary to request film with sprocket holes. It can be ordered from the National Weather Records Center in Asheville, N. C. for $4 per 100 foot reel. In most of the uses described above, more light can be obtained if the plates which serve to frame the filmstrip pictures are removed from the projector. (Figure 2) When a one liter flask of water is placed in front of the filmstrip projector beam, a .source of concentrated light is made possible, useful in demonstrating the refraction of light. This same method can be used to project concentrated light upward through a microscopic specimen.