![Sample our Engineering & Technology journals, sign in here to start your access, latest two full volumes FREE to you for 14 days]({"type":"image" , "src" : "/sda/5933/TOC-Subject-Sample-2021-Engineering-Tech.jpg"})
Abstract
In the instrument described, a light source of constant intensity illuminates the paper normally to the surface, and the light reflected at 4° to the normal falls on a photocell, the output of which is amplified and fed to a meter. By employing a ring reflector consisting of a portion of an ellipsoid, high photometric efficiency is obtained enabling very dense filters, such as interference filters, to be used.