is defined as an (absolute) parameter measurable by means of rigid scales and clocks. These same parameters
, however also describe with reference to the Gaussian system of coordinates the gravitational field which we have previously found to be identical with the physical cause of the metric. The case as to the validity of the special relativity theory for finite regions is characterised in that when the system of coordinates is suitably chosen, the values of
for finite regions are independent of
.
In accordance with the general theory of relativity the law of point motion in the pure gravitational field is expressed by the equation for the geodetic line. Actually the geodetic line is the simplest mathematically which in the special case of constant
, becomes rectilinear. Here therefore we are confronted with the transfer of Galileo's law of inertia to the general theory of relativity.