Radiation from platinum at high temperatures

The study of the emissive properties of substances which can be brought to high temperatures without undergoing chemical or physical changes of surface is important in optical pyrometry for the practical realization and measurement of high temperatures; for a knowledge of the emissive properties of platinum, for instance, at various temperatures, gives a ready means of obtaining true temperatures from observations of the ''black-body temperatures" as measured by an optical pyrometer. A platinum strip may replace to advantage an experimental black body, especially at temperatures above 1,500° C, and may conveniently serve as a luminous source for the comparison or calibration of optical pyrometers. It is the object of this paper to interpret the observations^ of Dr. Waidner and the author on the departure of platinum from blackbody radiation for red, green, and blue light, in terms of the now better known values of the higher temperatures involved, and as expressed by Wien's law as applied in a form first suggested by Lucas.* For a black body, Wien's law for the distribution of energy in the spectrum may be written