an alternating matrix, and denotes a space-time vector of the second kind. From the expressions (83), we obtain,

(85) |

from which we deduce that [see (57), (58)].

(86) | , |

(87) | , |

*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),

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) |

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

,
. |