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58
Relativity: The Special and General Theory
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 litttle consideration will show.
The following statements hold generally : Every physical description resolves itself into a number of
statements, each of which refers to the space?time coincidence of two events A and B. In terms of
Gaussian co?ordinates, every such statement is expressed by the agreement of their four
co?ordinates x1, x2, x3, x
4
.
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.
Next: Exact Formulation of the General Principle of Relativity
Relativity: The Special and General Theory