Data for the present summary were obtained from a number of members of Commission 22, and also from extensive literature which has grown greatly in the last three years (1961–1963). Communications, reprints and recommendations were sent by Astapovich, Babadjanov, Bakharev, Bogorodsky, Bronshten, Kashcheev, Krinov, Lebedinez, Tsesevich (U.S.S.R.), Fireman, Jacchia, McCrosky, Newkirk, O’Keefe, Olivier, Rinehart, Whipple (U.S.A.), Halliday, Millman, Nicholls (Canada), Ceplecha, Kresák (C.S.S.R.), Lovell (England), Hoppe (D.D.R.), Guigay (France), de Jager (Netherlands), Lindblad, B. A. (Sweden), Nielsen (Denmark), Hirose (Japan), Venter (South Africa), Öpik (Eire), Tomsen (New Zealand).