...There was a fundamental mistake…namely, the paying of attention solely to the result given by experimental measurements and entirely ignoring the inner realities of the inner processes.
Max Planck, The New Science, 1959.
Kirchhoff's Law is addressed in the following publication: P.M. Robitaille. On the Validity of Kirchhoff's Law of Thermal Emission. IEEE Trans. Plasma Science 2003, 31(6), 1263-1267.