266 IN STARRY REALMS. 



rial congruity, it seems impossible to doubt that Orion, the 

 finest constellation in the heavens, is not a mere fortuitous 

 concourse of stars, but is a system possessing indications of 

 a common origin. 



In a similar way we are entitled to infer that many other 

 remarkable groups of stars give evidence of a certain 

 physical connection which corroborates the presumption 

 obtained from the fact that the stars happen to be close 

 neighbours. I do not suppose that anyone ever could 

 have doubted that so striking a group as the Pleiades had 

 some natural connection. But if there were such doubts 

 they must be dispelled when the photographs of the Messrs. 

 Henry and of Mr. Roberts show the seven stars of the 

 Pleiades to be immersed in a single nebula, invisible to the 

 eye, and perceptible only to the delicacy of the photo- 

 graphic plate. In other famous groups also there are 

 indications of relationship drawn from their common 

 movements. If seven fish were seen near together in the 

 sea there would be a certain presumption that they formed 

 a related group, and this presumption would be greatly 

 strengthened if it should appear that all the fish were 

 swimming in parallel directions. We can sometimes apply 

 a similar principle to the study of a constellation. If 

 seven bright stars lie comparatively near each other in the 

 sky, and if it be found that they participate in a common 

 motion so far as direction is concerned, we may not un- 

 naturally conclude that those stars belong to an organized 

 system, and that they are not merely a number of discrete 

 objects scattered promiscuously on the sky. 



Picture this vast firmament of stars, some in associated 

 groups, some more sporadic and isolated, and all more or 



