GB416962A - Improvements in and relating to photo-metric apparatus - Google Patents

Abstract

416,962. Photometric apparatus. BRITISH THOMSON - HOUSTON CO., Ltd., Crown House, Aldwych, London.-(Assignees of Hardy, A. C. ; 28, Upland Road, Wellesley, Massachusetts, U.S.A.) Dec. 7, 1933, No. 34455. Convention date, March 10. [Class 97 (i).] In apparatus comprising a photoelectric cell receiving light alternately from a test source and from a standard, an optical system for controlling the light received by the cell comprises an angularly movable polarizing member, a double-image prism dividing the light incident upon it into two beams polarized in planes at right-angles, and a second polarizing member. The first polarizing member is continuously rotated and the second is angularly adjusted in accordance with the output of the photoelectric cell. As shown, the first polarizing member, comprising a Nicol &c. prism 10 is mounted within the hollow shaft 14 of a synchronous electric motor 16 and the second polarizing member 11 is mounted within a sleeve 20 rotatable by a knob 26 and having a pointer 21 moving over a scale 22. The double-image prism 12 is disposed between the members 10, 11. The light leaving the member 11 is received by the photoelectric cell 3, the output from which passes through an amplifier 4 to a vibration galvanometer 5. The member 11 is rotated by the knob 26 until the indicator 7 of the galvanometer is stationary ; the reading of the pointer 21 then gives the relative luminosity of the sources 1, 2. These are shown as primary sources, but they may consist of two different reflecting surfaces both receiving light from the same primary source. These surfaces may be arranged beyond the cell 3 so that the light from the single source passes through the members 10, 12, 11 before reaching the surfaces. In such an arrangement a spectroscope system may be arranged between the light source and the member 10 so that the surfaces can be illuminated bv monochromatic light. The light source and the slit plate of the spectroscope may be angularly adjustable to enable any desired part of the spectrum to be used. The two surfaces to be compared may be disposed within an integrating sphere having an outlet adjacent the photoelectric cell. The member 11 may be adjusted automatically by an electric motor controlled by the output from the cell. Specifications 291,397, [Class 97 (i)], and 341,200 are referred to.