  We argue that space-time geometry is not absolute with respect to the frame
of reference being used. The space-time metric differential form $ds$ in
noninertial frames of reference (NIFR) is caused by the properties of the used
frames in accordance with the Berkley - Leibnitz - Mach - Poincar\'{e} ideas
about relativity of space and time . It is shown that the Sagnac effect and the
existence of inertial forces in NIFR can be considered from this point of view.
An experimental test is proposed.
