The results of techniques developed and used to determine the mean effective emissivity of different surfaces over a range of temperatures from 100 to 800 F are presented. The measurement of radiant energy from the surfaces is accomplished by means of a 160-junction silver-constantan directional thermopile radiometer. Serious errors are noted and accounted for when improper use is made of polished shields in the experimental arrangements. This represents a refinement over previous techniques used; further refinements are anticipated with the ultimate aim of checking against integrated spectral data. However, the data presented are useful aids as a phase of the technique of evaluation of equilibrium temperatures of different surfaces exposed to solar irradiation.

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