Speed of EMR which includes light of course.. but I'll use RF reference. I have to admit of jumping to false conclusions.. where did I get the idea that the speed of light was constant.. Perhaps it was from the max limit imposed. I have been subconsciously worried over this for ages, because I knew wavelength was different for different materials for given f and wavelength = v / f eg In distilled water the waves travel only 20,000miles per second .. thats only 0.11 the speed of light in space. Therefore without the upper limit, why is it called a constant? and if aether experiments are to be interferometered why not send the light down crystal or glass or water filled tubes to get better resolution if short wavelength was the criteria for accurate resolution.. Or did I get something wrong.. Exciting times.. Philip.