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MANAGERS AND PROJECTIONISTS 259
Milton F. Fillius, contained in the Dayton transactions of the society. The data contained is the result of three complete sets of readings made by two different men, of each surface tested, so that apparently the liability of error is very small indeed. It is greatly to be regretted that kalsomine and paint surfaces were not tested, but the data nevertheless marks a very distinct step forward, since it provides the exhibitor and projectionist with a basis for intelligent comparison, as well as data which should enable him to select a screen surface suitable for use in the individual theatre by some other method than guess work, statements of salesmen or personal observation, none of which methods have very much value.
In making the comparisons a magnesium carbonate surface was selected as a basis, and its power of reflection was given an arbitrary value of 100 per cent. The reflection value of all other surfaces is therefore given as the percentage of reflection power of the magnesium carbonate surface.
In Table I is given a complete list of the materials measured.
The surface of the magnesium carbonate sample (1) was prepared by carefully scraping a block of the material with a steel straight-edge. The opal glass (2) was of the best quality obtainable for uniformity and whiteness, and the surface was carefully ground. The white blotting paper (3) was of the ordinary commercial quality used extensively in photographic work. The photographic stock (4) was a sample of uncalendered and uncoated material. No. 5 was of the same material but treated with the ordinary baryta coating.. The drawing paper (6) was the commercial grade of Wattman's hot pressed. Sample No. 7 was prepared by sandblasting a sheet of aluminum. No. 8 was made by sandblasting the front surface of an ordinary plate glass mirror. No. 9 consists of a screen made by superimposing a sample of the material such as is commonly used as the focusing screen in photographic apparatus upon the surface of an ordinary plate glass mirror.
The commercial screens examined and tested also are listed in Table II, beginning with No. 10. In the name column of Table II will be found the trade name applied to the surface by its manufacturer, in the texture column a qualitative statement of the character of the surface, and in the color column a qualitative statement of the color of the