http://en.wikipedia.org/wiki/Pound%E2%80%93Rebka_experiment "The Pound-Rebka experiment is a well known experiment to test Albert Einstein's theory of general relativity. It was proposed by Robert Pound and his graduate student Glen A. Rebka Jr. in 1959, and was the last of the classical tests of general relativity to be verified (in the same year). It is a gravitational redshift experiment, which measures the redshift of light moving in a gravitational field, or, equivalently, a test of the general relativity prediction that clocks should run at different rates at different places in a gravitational field. It is considered to be the experiment that ushered in an era of precision tests of general relativity. (...) When the photon travels through a gravitational field, its frequency and therefore its energy will change due to the gravitational redshift."
http://student.fizika.org/~jsisko/Knjige/Klasicna%20Mehanika/David%20Morin/CH13.PDF David Morin (p. 4): "This GR time-dilation effect was first measured at Harvard by Pound and Rebka in 1960. They sent gamma rays up a 20m tower and measured the redshift (that is, the decrease in frequency) at the top. This was a notable feat indeed, considering that they were able to measure a frequency shift of gh/c^2 (which is only a few parts in 10^15) to within 1% accuracy."
QUESTION: If, in a gravitational field, the speed of light varies exactly as the speed of cannonballs does, in accordance with Newton's emission theory of light, would Pound and Rebka have measured the same "frequency shift of gh/c^2"? It is easy to show that the answer is an unambiguous yes (Einsteinians occasionally admit that). How then can the Pound-Rebka experiment be "the experiment that ushered in an era of precision tests of general relativity"?