The radiant exchange problem for an isothermal spherical cavity having diffuse-specular walls is solved and the distribution of the local heat transfer for various opening angles and surface emissivities is obtained. Subsequently, the overall emission from the cavity (i. e., the apparent emissivity of the cavity) is calculated for various opening angles and surface conditions. In addition, the overall absorption characteristics of spherical cavities having purely specular walls is investigated analytically for the case of collimated radiation entering the cavity. Various opening angles and surface conditions are considered. The Monte Carlo method is utilized to support the results obtained from the analytical calculations. Results show that in spherical cavities the apparent emissivity is not very sensitive to the degree of specularity of the cavity wall. Also, there are situations in which the diffuse cavity is a more efficient emitter than a specular cavity. Absorption characteristic results show that for cavities having purely specular walls the absorption of collimated radiation is highly dependent on the angle of incidence of radiation on the opening for small opening angles. / Ph. D.