An elementary book on electricity and magnetism and their applications (1919)
Jackson, Dugald C. (Dugald Caleb), 1865-1951, Jackson, John Price, b. 1868, Black, Newton Henry, b. 1874 · New York, The Macmillian Co · leaf 523
nknownsource. It is also necessary tocut off all light from the testplate except that coming di-rectly from the lamp under test. After the illumination uponthe test plate, as previously described, has been determined, thevalue in foot candles is multiplied by the square of the distancein feet from… … Fig. 331. — Measuring illumination ona test plate directly in foot candles. ELECTRIC LIGHTING 469 greatly with conditions. In drafting rooms, theater stages,stores with dark merchandise, and in work with machineryrequiring delicate adjustment, bright illumination is required,which means 4 foot…
Electricity · Magnetism
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