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§ 21. From equations (Ia)—(Va) (§ 19) also some formulas can be derived, any of them contains only one of the magnitudes $$\mathfrak{d}_{x}$$, $$\mathfrak{d}_{y}$$, $$\mathfrak{d}_{z}$$, $$\mathfrak{H}_{x}$$, $$\mathfrak{H}_{y}$$, $$\mathfrak{H}_{z}$$.

At first, it follows from (IVa)

If we consider here what has been said in § 4, h, as well as the relations (Ia), (IIIa) and (4a), we arrive at the three formulas

Similarly, we find

The last members of these six equations are completely known once we know how the ions are moving.

Application to electrostatics.
§ 22. We want to calculate by which forces the ions act on one another, when all of them are at rest with respect to ponderable matter. In this case a state occurs, where at every point $$\mathfrak{d}$$ and $$\mathfrak{H}$$ are independent of time. We have

and equations (A) and (B) will be reduced, when for brevity's sake the operation