of the same events with reference to
vanishes. Pure "space-distance" of two events with respect to
results in "time-distance" of the same events with respect to
'. But the discovery of Minkowski, which was of importance for the formal development of the theory of relativity, does not lie here. It is to be found rather in the fact of his recognition that the four-dimensional space-time continuum of the theory of relativity, in its most essential formal properties, shows a pronounced relationship to the three-dimensional continuum of Euclidean geometrical space.[16] In order to give due prominence to this relationship, however, we must replace the usual time co-ordinate
by an imaginary magnitude