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 522
Illumination (foot candles) = zrr-:— ,,A R • Distance (ft.) squared ELECTRIC LIGHTING 467 Thus far we have assumed that there is only one source ofillumination and that the surface is perpendicular to the raysof light. In practice this is almost never the case, so that theproblem of computing or… … Fig. 330. — Macbeth illuminometer showing cross section. of them are really semiportable photometers with a scalecalibrated to read in foot candles. Figure 330 shows the Macbeth illuminometer. The cross sectionshows a tube with a sliding carriage for the standard lamp L and aglass prism P, which…
Electricity · Magnetism
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