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Moreover, according to this equation the time difference Δt′ of

two events with respect to K′ does not in general vanish, even

when the time difference Δt of the same events with reference to

K vanishes. Pure "space-distance" of two events with respect to K

results in "time-distance " of the same events with respect to K.

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.[14] In order to give due prominence

to this relationship, however, we must replace the usual time

co-ordinate t by an imaginary magnitude

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