But suppose we progressively diminish the time considered to a second, to a hundredth of a second, to a thousandth of a second, and so on.

As we pass along such a series we approximate to an ideal simplicity of structural relations of the pairs of events successively considered, which ideal we call the spatial relations of the Needle to the barge at some instant.

Even these relations are too complicated for us, and we consider smaller and smaller bits of the Needle and of the barge.

Thus we finally reach the ideal of an event so restricted in its extension as to be without extension in space or extension in time.

Such an event is a mere spatial point-flash of instantaneous duration.