For those who are still following this discussion...
Following a comment by James, I clarify my previous statement about
> "the limiting case when the total mass of the crystal is very large
> with respect to the mass of one photon"
I meant of course the "relativistic mass" of one photon [which is given
by h/(\lambda c)]. The rest mass of a photon is of course zero.
A photon of \lambda = 1 Angstroem has a relativistic mass of the order
of 10^{-32} kg. Certainly much smaller than the mass of even a
nano-crystal...
I was really just re-phrasing what Arthur Compton wrote in the quoted
paper [read the sentence just after his equation (9)].
--
Marc SCHILTZ http://lcr.epfl.ch
