The vector is perpendicular to w; we can call it the Magnetic rest-force.
Relations analogous to these hold among the quantities and Relation (D) can be replaced by the formula
We can use the relations (C) and (D) to calculate F and f from and , we have
and applying the relation (45) and (46), we have
Let us now consider the space-time vector of the second kind , with the components
Then the corresponding space-time vector of the first kind
vanishes identically owing to equations 49) and 53).
Let us now take the vector of the 1st kind
with the components
Then by applying rule (45), we have