Friedrich Kottler

“ If we treat as covariant, then this is evidently somewhat arbitrary in terms of Cartesian orthogonal coordinates, since covariants and contravariantes coincide here. If we would require (following Abraham) that the transform like the products of the corresponding components of the radius vector, then we would have to postulate the as contravariants. By passage to the reciprocal system we can, however, represent them as convariants. For the sake of being easier related to the integral forms, we stick to the covariant description. ”

“ It follows
with the known solution of Herglotz [2]
where
is the radius vector of the reference-point with respect to point . It is known, as to how the integration in the complex plane is carried out by means of a loop, which is clock-wise circulating around the negative imaginary semi-axis. To a fixed value system belongs a pole , for which we have
,
upon which the loop is to be drawn together; is then a light-point for , that is, is a minimal vector and is negative imaginary or lies on the pre-cone of (Minkowski) . ”

“ On the polar nature of and the axial nature of . The most general direction-changing transformations can namely always be traced back to a transformation multiplied by a change of direction of the coordinate axes. ”