Electrical engineer's pocket-book: a hand-book of useful data for electricians and electrical engineers (1901)
Foster, Horatio A. (Horatio Alvah), 1858-1913 · New York, D. Van Nostrand co.; London, E.& F.N. Spon, ltd. · leaf 403
h2If the lamp under test be at a height li above the horizontal plane of thephotometer and standard lamp or candle, other symbols remaining thesame, then c.p.ofthelamp= d, x J^- In Ritchies photometer two equal white surfaces are placed at anangle with each other, and with the line of light and… … Fig. 2. Prof. L. Webers Portable Photometer. j&yrton an«l Perry use what they call a dispersion photometer, inwhich a concave lens is used in the path of the stronger light to reduce itsintensity by dispersion of its rays to a known degree. This instrument is useful in measuring arc lamps.…
Electrical engineering
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