The Galactic System*

Abstract

THERE is a promontory on Mount Wilson from which the visitor to the Observatory can look down at night and see the lights of Pasadena and Los Angeles on the plain 7,000 ft. below. He cannot distinguish individual lights, but sees two patches of luminosity which indicate the outlines of the cities and the distribution of density—if not of population, at least of the street-lights. It is so easy to study this distribution from up here, and so difficult from inside the cities, where one cannot see the forest for the trees.