Light, photometry and illumination : a thoroughly rev. ed. of ''Electrical illuminating engineering'' (1912)
Barrows, William Edward, 1878-1960 · New York ; London : McGraw-Hill Book Co. · leaf 150
the intensity of whose light is varied by means of the rheostat, D. The lamp, C, is operated from two dry cells within theinstrument, a spring switch being placed in the circuit so thatthe cells are in use for a minimum time only. To effect a photo-metric setting, the amount of current through the… … Fig. 73.—The Marshal illuminometer by means of a simple Wheatstone bridge with a portable galvanom-eter, both inclosed within the instrument. One arm of thisbridge consists of a tightly drawn resistance wire, supported overa millimeter scale. The contact is moved along this exposedwire until the…
Light · Photometry · Electric lighting
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