SIDELIGHTS ON RELATIVITY

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qualities of the continuum of space-time differ in the environment
of different points of space-time, and are partly conditioned by the
matter existing outside of the territory under consideration.  This
space-time variability of the reciprocal relations of the standards
of space and time, or, perhaps, the recognition of the fact that
"empty space" in its physical relation is neither homogeneous nor
isotropic, compelling us to describe its state by ten functions (the
gravitation potentials g_(mn)), has, I think, finally disposed of
the view that space is physically empty. But therewith the
conception of the ether has again acquired an intelligible content,
although this content differs widely from that of the ether of the
mechanical undulatory theory of light.  The ether of the general
theory of relativity is a medium which is itself devoid of _all_
mechanical and kinematical qualities, but helps to determine
mechanical (and electromagnetic) events.

What is fundamentally new in the ether of the general theory of