Light is emitting from a source. Velocity of photon is always constant 'C' w.r.t stationary system. Say the source is moving at velocity 'V'. Then what is the velocity of photon at the instant of time before starting the emission?
Actually my problem is about "An analogous consideration—applied to the axes of Y and Z—it being borne in mind that light is always propagated along these axes, when viewed from the stationary system, with the velocity $\sqrt{c^2-v^2}$gives us" this line