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

glide and a sailboat to maneuver over tlie surface of water. There are many ways in which the wind affects the earth on which we live. Wind causes changes on the earth's surface by shifting sand which scour the rock formations by the cutting action of the moving sand. Valuable topsoil necessary for the growing of crops can also be removed by the wind. Violent storms develop from the wind's action and may cause much damage to propert>'. The seeds of tumbleweed, milkweed and cottonwood trees are scattered and sown by the wind. An experiment to demonstrate the expansion and contraction of air by warming and cooling is shown. A balloon is placed over the neck of a bottle and both are placed upon a hotplate. As the air in the bottle becomes warmer, the balloon begins to swell illustrating the expansion of air when heated. The bottle is then cooled in a bucket of ice water. The balloon collapses thus demonstrating the contraction of air when cooled. This same principle takes place around the earth's surface and is shown to the child by the use of animated diagrams. The atmosphere or blanket of air around the earth rises when warmed by the sun. This layer of air is then replaced by a layer of cooler air. The rising of warm air and the moving in of cooler air causes the winds and the swirling seas of clouds to form. This forming of clouds affects the weather which in turn gives the earth the moisture necessary for life upon its surface. Appraisal: Wind at Work was made in the ivestern part of the United States md its production is both instrucional and artistic. The result is a ilm useful for its aesthetic value as veil as for presenting science conjepts. Primarily geared for children n intermediate grade science classes, he film is general enough in presenation that it could be used with the ipper primary grades as an introducion to general scienc-e. The diagrams ised to demonstrate air movements ire clear and easily understood. The larrator explains that a special bottle lUSt be used in the experiment deminstrating the expansion and coniCtion of air. This safety precaution included to prevent possible injury uld children attempt this experiit by themselves, and is added ence of the careful thought given production. —Helen Dzur in any size room . . .with the AO Spencer GK Delineascope! The AO Spencer GK Delineascope will answer all your slide projection requirements. You can project any size slide from 2" x 2" to 3!4" x 4" . . . use it in average size classroom or the largest school auditorium. The entire optical system of each AO GK Delineascope is scientifically coUimated and precisely aligned like American Optical's finest research microscopes. In addition, only the GK has a calibrated lamp scale setting to accommodate for different focal length objectives. This eliminates the annoying "corner cut-off" and fuzzy color aberrations typical of most other lantern slide projectors when objectives of varying focal lengths are substituted. You're assured the best possible performance under even the most adverse projection conditions. In every way, optically and mechanically, the AO GK Delineascope is truly the standard for comparison . . . often imitated but never equalled by any other projector of its type. Learn how it can solve your slide projection problems! Send for information or ask your AO Representative for a convincing demonstration. merican Optical Company Dept. Namo S241 —Please send information on AO Si>encer GK ndineaacopc. -^1 would like n detnonfllration. INSTRUMiNT DIVISION. lUrFAlO IS, NIW YORK AddrefttuCily Zone— -Slate DUCATIONAL ScREEN AND AUDIOVISUAL GuiDE— MaY, 1961 235