moving system, which are enclosed by the surfaces mentioned above, then
If , we have the simple formula :—
It is to be noticed that the energy and the frequency of a light-complex vary according to the same law with the state of motion of the observer.
Let there be a perfectly reflecting mirror at the co-ordinate-plane , from which the plane-wave considered in the last paragraph is reflected. Let us now ask ourselves about the light-pressure exerted on the reflecting surface and the direction, frequency, intensity of the light after reflexion.
Let the incident light be defined by the magnitudes , v (referred to the system K). Regarded from k, we have the corresponding magnitudes :