1. Baade, W. and Mayall, N. U.: 1951, Symposium on the Motions of Gaseous Masses of Cosmical Dimensions, held at Paris in 1949; publ. as: Problems of Cosmical Aerodynamics, Central Documents Office, Dayton, O.
2. See, 1952, Sky Telesc. 11, 138.
3. 1. Schmidt-Kaler, Th.: 1965, Observational Aspects of Galactic Structure (ed. by A. Blaauw and L. N. Mavridis), Athens, p. XII-6
4. 2. also, 1964, Trans. IAU 12B, 416.
5. Ewen, H. I. and Purcell, E. M.: 1951, Nature 168, 356.