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On the Curvature of Space™ By A. Friedman in Petersburg * With one figure. Received on 29. June 1922 §1. 1. In their well-known works on general cosmological questions, Einstein' and de Sitter? arrive at two possible types of the universe; Einstein obtains the so-called cylindrical world, in which space has constant, time-independent curvature, where the curvature radius is connected to the total mass of matter present in space; de Sitter obtains a spherical world in which not only space, but in a certain sense also the world can be addressed as a world of constant curvature.* In doing so both Einstein and de Sitter make certain presuppositions about the matter tensor, which correspond to the incoherence of matter and its relative rest, i.e. the velocity of matter will be supposed to be sufficiently small in comparison to the fundamental velocity - the velocity of light.