Page:Grundgleichungen (Minkowski).djvu/45

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(92)

for .

Now if we make use of (59), and denote the space-vector which has as the x-, y-, z-components by the symbol , then the third component of 92) can be expressed in the form

(93)

The round bracket denoting the scalar product of the vectors within it.

§ 14. The Ponderomotive Force.

Let us now write out the relation in a more practical form; we have the four equations

(94)

,

(95)

,

(96)

,

(97)

.

It is my opinion that when we calculate the ponderomotive force which acts upon a unit volume at the space-time point x,y,z,t, it has got x-, y-, z-