226 
ASTRONOMY: H. S HAP LEY 
of which, in the galactic plane, is between 60 and 70 thousand light-years 
distant in the general direction of the dense star clouds of Sagittarius and 
Scorpio. 
The projection of the positions of clusters on a plane perpendicular to the 
Milky Way, and parallel to the direction of this center from the sun, is illus- 
trated in figure 3. The shaded portion of the diagram indicates the equatorial 
region, toward which globular clusters crowd but in which they are not found; 
its thickness appears to be only three or four per cent of its extent along the 
galactic plane. 
There can be little doubt that the galactic plane defined by the faint stars 
and by the Milky Way clouds is also a symmetrical and fundamental plane 
for the system of globular clusters. In other words, the distribution of clus- 
ters shows that, notwithstanding their great dimensions, they are subordinate 
FIG. 2. THE SYSTEM OF GLOBULAR CLUSTERS PROJECTED ON THE PLANE OF THE GALAXY 
The galactic longitude is indicated in the margin. The 'local system' is completely 
within the smallest circle, which has a radius of a thousand parsecs (3260 light-years). 
The larger circles, which are also heliocentric, have radii increasing by intervals of 10,000 
parsecs. The dotted line indicates the suggested major axis of the system (if ellipsoidal), 
and the cross the adopted center. The dots are about five times the actual diameters of the 
clusters on this scale. Nine clusters more distant from the plane than 15,000 parsecs are not 
included in this diagram. 
members of the far greater galactic system. Their arrangement and the rela- 
tive densities of various parts of the Milky Way clouds strongly suggest that 
the whole sidereal system is roughly outlined by the positions of globular clus- 
ters, and that all known celestial objects — stars, nebulae, clusters — are mem- 
bers of a single unit. 
The mean diameter of the proposed system appears to be at least 300,000 
light-years; its most conspicuous feature is the equatorial segment, which ap- 
parently is thickly populated with stars throughout its whole extent. From 
Auriga 
90° 
270° 
Scorpio 
