We now give a general outline of a classification of some of the brighter galaxies based on their integrated spectra. The investigation depends upon the rich spectroscopic and general photographic material of the Mount Wilson-Palomar and Lick Observatories. The Mount Wilson-Palomar spectrograms were obtained mainly by Humason, with a certain number by Hubble and Minkowski; the direct photographs were taken with the 200-inch, 100-inch, and 60-inch reflectors at Mount Wilson-Palomar, principally by Hubble, Humason, and Sandage. We wish to express our deep indebtedness for the opportunity to make use of this material.
The Lick spectrograms were taken principally by Mayall with the 36-inch Crossley reflector; the direct photographs were taken with the same instrument by a large number of observers over the past 50 years.
A number of galaxies could not be considered because the spectrograms were not of a type suitable for classification; others were omitted because the spectral lines were too faint to permit accurate classification. The remainder were classified and divided into groups according to spectral type. In all cases the spectral type refers to the principal contributors to the integrated light of the galaxy concerned.