The essence of Special Relativity is Einstein’s assumption of e = mc² for a massless photon and the mass of kinetic energy. This is the proper equation for the energy of moving matter but the proper equation for the photon is the reciprocal equation of cC = √e/m. Where Einstein made his mistake was his symbol of c² . Where the photon is concerned, c² is not the squaring of a single velocity but the multiplying together of two separate velocities c and C that may or may not be equal to c² . c is the relative velocity of photon measurement and C is the absolute velocity of photon spin. This experimental test will decisively measure the difference between Einstein’s idea of a massless photon of “pure energy” and the Newtonian principle of measurement of the momentum, force and energy of moving photon mass.