On the gravitational redshifts of spectral lines - A critico-historical   study
  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. 
A. Loinger, T. Marsico
physics.gen-ph