Compared with his outstanding achievements in mathematics and mathematical physics, the notable contributions of Hermann Weyl (1885-1955) to the subfield of physics "cosmology" are less well known. Nevertheless, during the period 1918 to 1930, in five editions of his bookRaum-Zeit-Materie(four of which differ) and in several articles, he was instrumental for the development of relativistic cosmological modeling by lending creative ideas to it. The most prominent of these ideas is what he himself, in an article in theclass="EmphasisTypeItalic ">Encyclopedia Britannica(Weyl 1926e), called "Weyl's hypothesis' and which was taken up by other authors as "Weyl's postulate" (Robertson 1933, Narlikar 1979, Raychaudhuri 1979) or as "Weyl's principle" (Weinberg 1972). It is the assumption that there exists a common rest system^sfor the galaxies and that their worldlines originate in a common point in the past (Weyl 1923e). Weyl also found an exact, spherically symmetric static solution of Einstein's field equations with cosmological constant for incompressible matter (RZM, RZM³1919, 1919d). He also was one of the first scientists calculating an (approximately)linearrelation between the redshift of galactic spectra and distance (Weyl 1923e).