The use of the solar furnace for investigating properties of materials has received increased attention. However, such work has been limited to determining physical properties of refractory materials. Analyses of performance, related to such work, have been confined to investigations of flux distribution and temperature on flat-plate, hemispherical, and cavity receivers at the focal spot. Heat conduction away from the focal spot usually has not been considered. The present investigation is concerned with the analysis of fluxes and temperatures that can be attained in tensile specimens undergoing mechanical tests. Account is taken of heat loss by conduction and reradiation. It is shown that, (a) attainable temperatures are considerably lower than those reached in flat-plate receivers, (b) with normal low-aperture furnaces (i. e., 60 deg) a large furnace is necessary to reach high temperatures with adequately large specimens, and (c) furnaces best-adapted to mechanical testing would have larger apertures (120 deg) than are now commonly conceived.