This equation expresses the law of observation in its most general form. If Φ = π/2, the equation takes the simple form
v
cos Φ′ = ---
c
We have still to investigate the amplitude of the waves, which occur in these equations. If A and A′ be the amplitudes in the stationary and the moving systems (either electrical or magnetic), we have
If Φ = 0, this reduces to the simple form
From these equations, it appears that for an observer, which moves with the velocity c towards the source of light, the source should appear infinitely intense.