Friedrich Kottler

“ The world lines of constant curvatures correspond to a constant magnitude of the first acceleration in Newtonian mechanics, and furthermore to a common helix or its variations: a circular line or straight line as hodograph of the velocity. ”

“ Generalizations to curves, in which only is constant. One could say: “The passage from one point to a consecutive causes an orthogonal (infinitesimal) transformation of the comoving tetrad; for such one, however, the fundamental equations are covariant according to the relativity principle, thus invariant in a suitable reference system, namely the tetrad in ; now, if I define a reference-point fixed in the tetrad , thus
where the are constants satisfying the condition , do the fields in have to be constant in the general case of an arbitrary world line ?” ”

“ The mutual influence is therefore constant in a system or ; the electron, whose points describe such world lines as and (thus curves of constant curvatures belonging to one and the same family) , retains its shape in such a continuously varying reference system . ”