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ASTRONOMY: H. SHAPLEY 
color indices in the globular cluster Messier 13 indicated the absence of 
scattering of light in space,^ the similar properties of the faint stars in 
Messier 1 1 and the galactic clouds show that in this direction also hght 
is not appreciably diminished by scattermg. 
5. The present investigation contributes to the problem of the color 
of the faint stars, and consequently, if space absorption is accepted as 
ineffective, to the question of the extent and character of the galactic 
system. The increase of the minimum color index with decreasing 
brightness has been observed by Scares^ for the north polar stars, 
galactic latitude +28°, by Hertzsprung^ and Scares' in the open cluster 
RELATION BETWEEN COLOR AND LUMINOSITY IN MESSIER 11. ABSCISSAE ARE 
COLOR CLASSES; ORDINATES ARE APPARENT MAGNITUDES. 
N. G. C. 1647, galactic latitude —15°, by the present writer in and 
around Messier 67,^ galactic latitude +34°, and in the neighborhood of 
Messier 13, galactic latitude +40°. In none of these fields have very 
small or negative color indices appeared among the fainter stars;"' and a 
definite, accessible limit to the galactic system was thus suggested, at 
least for the higher galactic latitudes. The first divergence from this 
tendency was found in the field of the variable star XX Cygni,^^ galactic 
latitude +13°, where 13th magnitude stars of color h were found, as 
well as a number of faint a's. Similarly, faint blue stars have been 
recently observed by the writer in the region of the Perseus cluster, 
