stitute the only actual evidence of a time-space nature with which we meet in physical statements.
When we were describing the motion of a material point relative to a body of reference, we stated nothing more than the encounters of this point with particular points of the reference-body. We can also determine the corresponding values of the time by the observation of encounters of the body with clocks, in conjunction with the observation of the encounter of the hands of clocks with particular points on the dials. It is just the same in the case of space-measurements by means of measuring-rods, as a little consideration will show.
The following statements hold generally: Every physical description resolves itself into a number of statements, each of which refers to the spacetime coincidence of two events and . In terms of Gaussian co-ordinates, every such statement is expressed by the agreement of their four co-ordinates , , , . Thus in reality, the description of the time-space continuum by means of Gauss co-ordinates completely replaces the description with the aid of a body of reference, without suffering from the defects of the latter mode of description; it is not tied down to the Euclidean character of the continuum which has to be represented.
