The consequences of his idea and, in particular, the enormously greater photic energies in the past, make it untenable. Neville. I take it you are taking photons as equivalent to mass, and that therefore increased speed = increased energy... I wonder. Is the energy of EMR dependent upon the speed? Is the energy of EMR entirely in the corpuscular (Photon) element or is it distributed between the wave and corpuscular. ? Or even betwen the electrostatic and magnetic fields, which might mean the same thing. If the speed changes, the wavelength will change if the frequency is to be unchanged. The only practical example I can offer is the electrical characteristic of RF current in a conductor. The speed of propagation of the electroagnetic field in the metal slows down to make the physical wavelength much shorter than it would be in space, 0.6 if I recall, yet the power frequency and energy is unchanged. The question we are asking then, is, can this constant for the speed of light in a vacuum be changed? Energy should not come into the equation. Technical: The velocity of EMR through a medium depends upon the dielectric constant of the medium, which for a vacuum is taken as unity, 1. Air is taken as close enough to 1. If the dielectric constant is greater than 1 the velocity is reduced. It is the introduction of insulating material with a high dielectric constant that slows down the velocity of propagation, not the metal conductor. Philip.