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The article discusses the increasing use of visual aids by science teachers in the U.S. Appropriate visual aids may effectively supplement any experience. Motion pictures play an important role in teaching of almost any course while home-made slides are particularly valuable for science teaching. The simplest of these are the glass and the cellophane slides. These slides are easily made from common materials without photographic supplies or any particular skill. Fine emergy or carborundum powder are the abrasives which are used for making ground glass slides. The slides should be thoroughly used before they are used either for coating or for writing upon directly with ink. Dipping the slides in alcohol and wiping with a clean piece of cheese cloth is also an effective method. The main advantage in using ground glass slides is that they may be written upon with an ordinary pencil, and can be colored with either special lantern slide crayons or lantern slide inks.

This article reports on how abrasion from toothbrushes and dentifrices affect dental enamel. The article discusses the ingredients, abrasive particles, and hydrogen-ion concentrations in dentifrices, noting correlations between teeth size and how they are affected by different particle sizes. Information is also presented on calcium carbonate, dicalcium phosphate, and abrasive powders.

The use of an Accelerotor abrasion tester is discussed, and the abrasion-resistance of several plain-weave fabrics is shown to depend on the type of fibre. The materials are ranked in order of decreasing resistance to abrasion with carborundum, rubber, metal, and plastics abradants. Polyamide fibres have outstanding resistance and cellulose-ester and regenerated protein fibres poor resistance to abrasion. The order of resistance of other synthetic-polymer fibres, regenerated cellulosic fibres, and natural fibres is shown to alter slightly according to the nature of the abradant, the linear density of the fibre, and the sett of the fabric. The results are in general agreement with published data, but the resistance of polypropylene-fibre fabrics is lower than it was expected to be. Microscopical examination of detritus confirmed that this consisted of small segments of complete fibre, which indicated that abrasion occurs by fibre breakage. A useful correlation is established between the specific strength and initial modulus of a fibre, or the energy of rupture of mechanically conditioned fibres, and the abrasion-resistance of a fabric. [ABSTRACT FROM AUTHOR]