Published in PASP 69, 1957.

Table of Contents

• INTRODUCTION
• GENERAL CHARACTERISTICS OF THE SPECTRA OF GALAXIES
• Humason's Spectral Classification System
• Criteria for a Spectroscopic Classification of Galaxies
• THE SPECTRUM OF THE ANDROMEDA NEBULA (M 31)
• The Spectrum of the Nuclear Region
• A Hypothetical H-R Diagram for the Inner Region
• The Spectrum of the Main Body
• A Comparison of the Spectra of M 31 and M 33
• SPECTRA OF IRREGULAR GALAXIES LIKE THE LARGE MAGELLANIC CLOUD
• A SPECTRAL CLASSIFICATION OF GALAXIES
• The A-systems
• The AF-Systems
• The F-Systems
• The FG-Systems
• The K-Systems
• THE RELATIONSHIP BETWEEN FORM AND SPECTRUM
• A POSSIBLE LUMINOSITY EFFECT IN THE SPECTRA OF THE K-SYSTEMS
• CONCLUSION
• REFERENCES