The top of a tower of height h emits light with frequency f, speed c and wavelength L (as measured by the emitter):

f = c/L

An observer on the ground measures the frequency to be f'=f(1+gh/c^2) (confirmed by Pound and Rebka), the speed of light to be c' and the wavelength to be L':

f' = c'/L'

Crucial questions:

c' = ?

L' = ?

Newton's emission theory of light says:

c' = c(1+gh/c^2)

L' = c'/f' = L

Einstein's general relativity says:

c' = c(1+2gh/c^2)

L' = c'/f' L

The increase in wavelength (L'L) implied by general relativity is obviously absurd, which means that the Pound-Rebka experiment has actually confirmed Newton and refuted Einstein.

References showing that, according to Einstein's general relativity, in a gravitational field the speed of light varies in conformity with the equation c'=c(1+2gh/c^2):

http://arxiv.org/pdf/gr-qc/9909014v1.pdf
Steve Carlip: "It is well known that the deflection of light is twice that predicted by Newtonian theory; in this sense, at least, light falls with twice the acceleration of ordinary "slow" matter."

http://www.speed-light.info/speed_of_light_variable.htm
"Einstein wrote this paper in 1911 in German. (...) ...you will find in section 3 of that paper Einstein's derivation of the variable speed of light in a gravitational potential, eqn (3). The result is: c'=c0(1+phi/c^2) where phi is the gravitational potential relative to the point where the speed of light co is measured. (...) You can find a more sophisticated derivation later by Einstein (1955) from the full theory of general relativity in the weak field approximation. (...) Namely the 1955 approximation shows a variation in km/sec twice as much as first predicted in 1911."

http://www.mathpages.com/rr/s6-01/6-01.htm
"Specifically, Einstein wrote in 1911 that the speed of light at a place with the gravitational potential phi would be c(1+phi/c^2), where c is the nominal speed of light in the absence of gravity. In geometrical units we define c=1, so Einstein's 1911 formula can be written simply as c'=1+phi. However, this formula for the speed of light (not to mention this whole approach to gravity) turned out to be incorrect, as Einstein realized during the years leading up to 1915 and the completion of the general theory. (...) ...we have c_r =1+2phi, which corresponds to Einstein's 1911 equation, except that we have a factor of 2 instead of 1 on the potential term."

http://arxiv.org/ftp/arxiv/papers/1111/1111.6986.pdf
J.D. Franson, Physics Department, University of Maryland: "According to general relativity, the speed of light c as measured in a global reference frame is given by:

c = c0(1 + 2phi/c0^2) (1)

where c0 is the speed of light as measured in a local freely-falling reference frame."

Pentcho Valev