THE MOVEMENTS OF THE STARS. 265 



changing. We sometimes think that those groups of stars 

 to which from all antiquity certain names have been 

 assigned have bonds of affinity, and that their proximity 

 on the heavens is not to be attributed to a mere casual 

 arrangement, but is to be taken as indicating a community 

 of origin. In some cases there can be no doubt that this 

 is so. In the great group of Orion, for instance, to which 

 I have already referred, modern researches demonstrate 

 that the several stars of that grand constellation possess a 

 structure which may be described as peculiar to themselves, 

 inasmuch as a similar structure has only been observed 

 in one other star in the sky except those of Orion. In 

 this case we have the evidence not only of juxtaposition in 

 the heavens, but also of an allied material composition. 

 Under these circumstances it seems almost impossible to 

 doubt that the glorious assemblage of stars ferming the 

 constellation of Orion does really represent portions of a 

 mighty system. If any further corroboration of this view 

 be required, it may be obtained from recent discoveries 

 with respect to the peerless nebula by which Orion is most 

 familiar to astronomers (p. 126). The beautiful photographs 

 which have been obtained by Common and other astrono- 

 mers have tended to disclose ever widening boundaries 

 to the great nebula when sufficiently long exposure has 

 been given. We thus see that the glowing gas encroaches 

 on the surrounding space to an extent much wider than 

 mere eye observation would have indicated. Several of 

 the bright stars are already seen to be invested with 

 whatever glory residence in the interior of a glowing 

 nebula may confer. Adding this circumstance to those 

 we have already mentioned of juxtaposition and of mate- 



