At the Istituto Termometrico Italiano a spherical cavity has been constructed as a radiation source in absolute temperature measurements. In theoretical prediction of its effective emissivity, a discrepancy appears between Gouffé’s and DeVos’s formulas. In this paper the authors discuss the approximations involved in DeVos’s process and report corrections suitable to improve the precision of the results. With such corrections, computations based on both formulas agree within a wide variation range.
P. Campanaro and T. Ricolfi, "Effective Emissivity of a Spherical Cavity," Appl. Opt. 5, 929-932 (1966)