  A beautiful, detailed computation by Whittaker has enabled us to prove in a
rigorous way that the gravitationally redshifted frequency of a monochromatic
e.m. wave sent forth at the surface of a celestial body is propagated unaltered
from the emitting source to terrestrial observers. We remark that in the
customary treatments only qualitative and inaccurate justifications of this
fact are given.
