The solution of many calorimetric problems demands a precise knowledge of the radiation of specimens. As far as nonblack objects are concerned, this means determining the emissivity e of the system. In the method here proposed, the temperature of the front surfaces of the rotationally symmetrical specimen, which is enclosed in a cylindrical vacuum vessel, is held constant. For a given emissivity, a characteristic temperature distribution is found. The calculated relation has been numerically processed with a Siemens 4004 computer and graphically plotted. A detailed investigaton of the usefulness of this method shows that e can be determined to within about 5%.