Secular Changes of the Units and Constants of Physics

Abstract

GERHARZ¹ has recently proposed a new method for determining the velocity of light in terms of a standard frequency and of the wave-length of an atomic radiation. He expects to reduce his experimental errors to less than 1 part in 10⁸ and suggests that it should then be possible to obtain evidence about secular changes in the velocity of light. Dingle², on the other hand, follows Clemence in arguing that if the unit of time is defined in terms of the frequency of some atomic transition and that of length in terms of the wave-length of an atomic radiation, then the velocity of light is implicitly constant, no evidence can be obtained of its changes relative to atomic constants, and the science of physics is restricted at its foundations. The conflict between these two statements shows that the meaning of such phrases as ‘secular changes in the velocity of light’ needs clarification.