Abstract: | RIEMANN himself has considered his formulation of the differential geometry of curved spaces as a first step to a unified geometrical theory of “one ether of gravity, electricity and magnetism”. RIEMANN has pointed out that a fundamental point in such a theory of gravitation has to be the asymmetry of its sources: only positive masses exist. – According to RIEMANN this asymmetry of sources to be coupled with an asymmetry of gravitation field equation against the time-reversion t → - t. Therefore, the gravitation field equation is of the type of a continuity-equation of a velocity field vi?gikθ k Φ. RIEMANN 's ether is incompressible in empty space-domains: θ k (g1/2vk) = o. But, in domains with a massdensity σ > o it is θg1/2/θt = ?2 kcσ = ? 2 kcg1/2σ0 (with a universal constant kc). The matter-density defines depressions of the ether. In a general-relativistic approach RIEMANN 's ansatz means that in empty space-time domains the world-geometry is the purely metrical “RIEMANN ian” geometry. However, in domains with a non-vanishing matter-tensor Tμv ≠ o the geometry becomes “non-RIEMANN ian” affine connecting and is of the type of WEYL 's geometry or of the “EINSTEIN -CARTAN theories of gravitation”. Especially, RIEMANN 's field equation for the empty space θ k ((g1/2gikθ k Φ) = o. is the EINSTEIN equation (-|gμv|)1/2 R00 = o with g00 = - Φ2c-4. |