Page:Zur Elektrodynamik bewegter Systeme II.djvu/12

 Since we measure electromagnetic forces with respect to bodies which are at rest with respect to Earth or moving slowly at least, the value which $$f$$ assumes for $$u=p=const.$$ is most important. We obtain it in the most vivid form, by again introducing local time $$t'$$ by means of (6). Then, it follows from (29) by means of (7), or more simple by means of:

and

directly from (28):

Here, it is by I'b to IIIb:

thus it follows:

where

The value in (31), considered as a function of relative coordinates and local time, doesn't explicitly depend on $$p$$; but also not implicitly, since according to § 3, also E, M and $$\Lambda$$ are functions (independent from P) of the same four variables. With respect to stationary states it becomes $$f=f_0$$. Furthermore, it is irrelevant for the representation of these states, as to whether we use local time or general time. Thus the approach is given: the forces of the stationary field in relatively resting bodies are in all rigor independent from Earth's motion. It additionally gives the amount of these forces in the well-known form, which forms the expression of all certain experiences.