Many years ago Poincare convincingly demonstrated that space geometry
does not have a meaning in itself, but only within the aggregate ''geo
metry + measuring instruments.'' Hitherto, this result did not manifes
t itself in physical theory, which proceeded along another path and ad
mitted solely a dependence of space-time geometry on the matter-energy
momentum tenser. In this paper it is shown how the fact, stated by Po
incare, can manifest itself in space-time properties of noninertial fr
ames of reference.