May 25, 1917] 



SCIENCE 



525 



Fig. 14. The Milky Way around Bho Ophiuchi, photographed by Barnard with the 10-ineh 

 Bruce Telescope of the Yerkes Observatory. 



the nebula is. A similar deficiency of faint 

 stars exists within the great nebula of 

 Orion, and likewise in the adjacent areas, 

 where Mr. William H. Pickering has found 

 a very large part of the constellation of 

 Orion to be covered with faint nebulosity. 

 We shall give illustrations of several regions 

 (see Figs. 14, 15, 16) where this condition 

 — the presence of nebulosity and the scar- 

 city of faint stars — ^is so marked as to be at 

 once apparent. There are so many regions 

 in and near the Galaxy' where these rela- 

 tionships exist that we can not doubt their 

 significance. The faint stars are relatively 

 scarce chiefly because the nebular materials 

 cut off the light of the more distant stars. 



This explanation is reached by several lines 

 of evidence, but we take time to present 

 only one. 



It is established by modern astronomy 

 that the individual stars are in rapid mo- 

 tion. The speeds of the naked-eye stars 

 average about sixteen miles per second. 

 The distant fainter stars, so far as they 

 have been observed, are also traveling 

 rapidly. There is a tendency to favor cer- 

 tain directions of motion, and the stars in 

 certain small groups are keeping company 

 through space ; but a large share of stellar 

 motion is at random. There are stars 

 traveling in all directions. We have not 

 the direct evidence as to the motions of the 



