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ROBERT M. YERKE3 AND JOHN B. WATSJN 



Figure 1 — Perspective of light or " brightness " apparatus. A, light box; C, D, 

 compartments of A; B, partition between (" and D; E, F, lids of A; G, H, 

 metal carriages carrying tungsten lamps; IJ antl KL, tracks for G and H; 

 M, N, Starrett steel millimeter tapes; O, P, apertures covered by Aubert dia- 

 phragms; R, Bausch and Lomb cooling cell in light box; d, d', metal straps; 

 y, aluminum f)late sliding between d and d'; T, tracks for y; V, stop for y; 

 "z, steel plate bolted to wooden end of light box; h, screws attaching y to z; 

 s, s, standard brass stimulus plates; p, brass frame about aperture in y; r, 

 hard rubber ring screwed to p. 



