National Geographic : 1951 Dec
0 National Geographic Society 765 Ektachrome by Willard I1. Culver A Huge Hollow Sphere Tests the Brilliance of Ordinary Electric Lights When the sphere is closed, light from the sample lamp inside is diffused equally over the interior. Light coming from one small hole gives an accurate measure of the lamp's total output and helps set electric light standards. ****~~~*'---""°"""""""*"