where the integrals only have to be extended over the ponderable body, but like in § 13, it should taken for the entire space enclosed by .
At first, we replace , etc. by the expressions (10), and, because of (I), by
thus
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(14)
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Furthermore, a partial integration and application of (IV) and (II) gives (when we denote the direction constants of the perpendicular to by )
If we substitute this value into (14), then several terms occur, that can be completely integrated, and eventually by a simple transformation