The Predicted Shift of the Fraunhofer Lines

EINSTEIN'S prediction of a shift of the Fraunhofer lines to the red can be analysed into two assertions:- (1) That the period of vibration of an atom at rest on the sun differs from that of a similar terrestrial atom; and (2) that this difference is preserved unchanged by the light-waves travelling from the solar atom to the earth, so that it is revealed by a comparison made in a terrestrial laboratory. It is the second assertion that is challenged by Mr. Rice; and, so far as I can make out, the same objection was at the root of the criticisms formerly made by Sir Joseph Larmor. Since criticism centres entirely round the second assertion, I will deal with it solely. I may state, however, that although I regard the first assertion as highly probable, I do not regard it as proved with complete rigour; and had the criticism been directed against this, I should have been much less willing to take sides in the controversy.