A treatise on architecture and building construction (1899)
International Correspondence Schools · Scranton, The Colliery engineer co. · leaf 194
. One of the oldest of these instruments, called the Rum-ford photometer, is shown in Fig. 94. It consists of a tablehaving a black wooden post r, standing erect as shown, anda screen g, which receives the shadows of the post that are 16 PLUMBING AND GAS-FITTING. 163 cast by the lights a and b. The… … lines until the shadows e and/appear of exactly equal black-ness. The powers of the two lights are then computed bydividing the square of the distance b c by the square of thedistance a c, the quotient being the candlepower of thelight b. This method is very inaccurate, and is not to be…
Architecture · Building
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