ASTRONOMY: H. SHAPLEY 
225 
available astronomical records contain 69 clusters that appear definitely to 
belong to the globular classification. Further work on very faint and distant 
objects will probably add a few to the present list, but within a distance of 
100,000 light-years of the sun the survey appears to be complete. Keeping 
this limitation in mind, we may examine the collected data for signs of a gen- 
eral organization. 
The apparent concentration of the globular systems to a southern region of 
the Milky Way has long been known. It now appears, upon closer investiga- 
tion, that few if any typical globular clusters are to be found within 5° of the 
galactic plane; and, when actual positions in space are substituted for appar- 
ent positions, this suggested avoidance of the mid-galactic region reveals 
0 10 20 30 40|' s »5Pm O /6CF 
i 1 1 1 : 1 >' n — : ' "A i I \J i~ ' 
-20 1 I I I 
FIG. 1. DISTRIBUTION OF CEPHEID VARIABLES 
The unit of distance is 100 parsecs. Ordinates are distances from the galactic plane; 
abscissae are projected distances in the plane. Open triangles and black dots designate, re- 
spectively, cluster-type variables and Cepheids with periods in excess of a day. The near- 
est globular cluster, co Centauri, is just outside the boundary of the diagram on the right. 
RU Bootis, indicated by an arrow, is too far above the plane to fall within the figure. The' 
semicircles, with radii of 500 and 1000 parsecs (tt = 0".002 and0".001), indicate how distant 
most of these variables are as compared with the average star of the tenth magnitude or 
brighter (x > 0".004, Kapteyn). Between the broken horizontal lines, ±1750 parsecs, lies 
the equatorial galactic region devoid of globular clusters. 
itself as a total absence of compact clusters from the domains of space that 
appear to contain most of the known sidereal bodies. 
The striking distribution of globular clusters in galactic longitude is well 
shown in the projection of their positions on the galactic plane in figure 2. 
Apparently the clusters themselves form a large flattened system, the center 
