  This article is devoted to the results of an experimental test of the
theoretical assumption that the basic axiomatic postulate of statistical
physics according to which it is equally probable for a closed system to reside
in any of the microstates accessible to it may be invalid for nonergodic cases.
In the course of photometric experiments for the purpose of recording the
predicted loss of isotropy by a diffuse light field when it came into contact
with a two-dimensional phase-type diffraction grating, a significant deviation
from Lambert's law was detected when the diffuse photon gas was scattered by
the grating surface. This caused angular anisotropy of the radiation fluxes to
appear in the initially homogeneous light field. These results provide a basis
for revising the determination of the most probable macrostate of a closed
system.
