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then the length of the first electron will have to be denoted by the section $P'P'$ of the corresponding strip parallel to $OC'$. And we will find the first electron shortened in relation to the second one exactly in the ratio given above; for in the figure

$P'P':Q'Q'=OD:OC'=OD':OC=QQ:PP.$

Lorentz named the combination $t'$ of $x$ and $t$ the place-time of the uniformly moving electron and appropriated a physical construction of this notion for the better understanding of the hypothesis of contraction. Nevertheless, it is the merit of A. Einstein^[1] to have clearly recognized, that the time of one electron is as good as that of the other; in other words, that $t$ and $t'$ are to be treated alike. Therewith, first of all, time, as a notion uniquely determined by the phenomena, was dropped. Neither Lorentz nor Einstein shook the notion of space, perhaps for this reason that with the aforesaid special transformation, in which the $x',t'$-plane is congruent with the $x,t$-plane, an interpretation is possible as if the $x$-axis of space remained unchanged in its position. Also, to march over the notion of space (as in the case of the notion of time) is to be appraised as the rashness of mathematical refinement. After this further progress, which is, however, indispensable for the true understanding of the group $G_{c}$, the word postulate of relativity, for the demand of an invariance with the group $G_{c}$, appears to me very stale. As the sense of the postulate becomes, that only the four-dimensional world in space and time is determined by the phenomena while the projections in Space and in Time may be still taken in hand with a certain freedom, I should rather like to give this statement the name Postulate of the absolute world (or briefly world-postulate).

1. Annalen der Physik, 1905, p. 891; Jahrbuch der Radioaktivität und Elektronik, 1907, p. 411.