an alternating matrix, and denotes a space-time vector of the second kind. From the expressions (83), we obtain,
(85)
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from which we deduce that [see (57), (58)].
(86)
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,
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(87)
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,
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When the matter is at rest at a space-time point,
, then the equation 86) denotes the existence of the following equations
;
and from 83),
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Now by means of a rotation of the space co-ordinate system round the null-point, we can make,
;
According to 71), we have
(88)
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and according to 83),
. In special eases, where
vanishes it follows from 81) that
and if
and one of the three magnitudes
are
, the two others
. If
does not vanish let
, then we have in particular from 80)
and if
. It follows from (81), (see also 88) that
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,
.
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