The Absolute Photographic Magnitude of Supernovae.

A compilation of the photometric data for the i8 supernovae known at the end of 1937 is given. Former estimates have been replaced by photometric magnitudes after a redetermination of the magnitudes of comparison stars on the international system. The mean absolute photographic magnitude of the supernovae, derived from this material, is Mmax = -14.3 ± 0.42 (me.) with a dispersion ~ 1.1 mag. This result, together with the spectroscopic evidence, fully confirms the view that two classes of novae, common novae and supernovae, exist. Attention is drawn to the curious fact that 72 per cent of the known supernovae appeared in late-type spirals. B Cassio- peiae and the Crab nebula, which may have been galactic supernovae, are discussed