Contributions by: Harlow Shapley, Carleton S Coon, Paul B Sears, Hurd C Willett, H Wexler, John Wolbach, Donald H Menzel, Barbara Bell, P L Bhatnagar, Max Krook, A J J Van Woerkom, Dirk Brouwer, Richard Foster Flint, John T Hack, C C Nikiforoff, J Laurence Kulp, Edmund Schulman, John H Conover, Victor Conrad, Elso S Barghoorn, Edwin H Colbert, Edward S Deevey Jr