Page:Zur Elektrodynamik bewegter Systeme II.djvu/4

 By means of (5), (7) and (8), two equations emerge from I' II', which shall be simplified by putting:

Then it is given:

§ 3. The field in relatively resting media.

Let the only velocity of the system be $$p$$, or which is the same, let it be in relative rest. Then $$v=0$$, and the following equations – in all rigor – shall apply:

These equations have exactly the same form, as 's equations for a stationary system. Only by those equations, however, the field E, M and thus also the radiation relative to matter $$\Sigma$$ is determined, as far as certain quantities – "electric and magnetic quantities" – which are invariable according to those very equations, are required. Thus for a while we postpone the consideration of these processes in which electromagnetic energy goes over into other forms of energy, especially mechanical work, and then we can say: