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 148
esthrough the prisms P and Q to the prisms W and A^, these beinga Wallaston and Nichol prism respectively. The direct raysfrom the standard comparison lamp pass direct to the prismsW and N. At W the rays from the two sources are divided intobeams polarized in planes at right angles to each other.… … Fig. 71.—The Preece and Trotter photometer. intensity of one field will be increased in brightness and theother decreased. It is obvious that a scale attached to thecircle B can be so calibrated that the position of a pointer at-tached to the prisms at A^ will indicate the measurement when…
Light · Photometry · Electric lighting
Internet Archive · Boston Public Library · Public Domain Mark 1.0. Free to use for anything.
