10 Notes on Star-Streams. 



I have indicated is considered to be really referable to a 

 systematic distribution, the theory of a stratum of stars dis- 

 tributed with any approach to uniformity, either as respects 

 magnitude or distance must be abandoned. It seems to me 

 to be also quite clear that the immense extent of the galaxy 

 as compared with the distances of the c lucid ' stars from us, 

 could no longer be maintained. On this last point we have 

 other evidence, which I will briefly consider. 



First, there is the evidence afforded by clusterings in the 

 Milky Way. I will select one which is well known to every 

 telescopist, namely, the magnificent cluster on the sword-hand of 

 Perseus. No doubt can be entertained that this cluster belongs 

 to the galactic nebula, that is, that it is not an external cluster : 

 the evidence from the configuration of the spot and from the 

 position it occupies, is conclusive on this point. Now, within 

 this spotj, which shows no stars to the naked eye, a telescope 

 of moderate power reveals a multitude of brilliant stars, the 

 brightest of which are of about the seventh magnitude. Around 

 these there still appears a milky unresolved light. If a telescope 

 of higher power be applied, more stars are seen, and around 

 these there still remains a nebulous light. Increase power 

 until the whole field blazes with almost unbearable light, yet 

 still there remains an unresolved background. "The illustrious 

 Herschel" says Professor Nichol, "penetrated, on one occasion, 

 into this spot, until he found himself among depths, whose 

 light could not have reached him in much less than 4000 years; 

 no marvel that he withdrew from the pursuit, conceiving that 

 such abysses must be endless." It is precisely this view that I 

 wish to controvert. And I think it is no difficult matter to 

 show at least a probability against the supposition that the 

 milky light in the spot is removed at a vast distance behind 

 the stars of the seventh magnitude seen in the same field. 



The supposition amounts, in fact, to the highly improbable 

 view that we are looking here at a range of stars extending in 

 a cylindrical stratum directly from the eye — a stratum whose 

 section is so very minute in comparison with its breadth, that, 

 whereas the whole field within which the spot is included is but 

 small, the distance separating the nearest parts of the group 

 from the farthest, is equivalent to the immense distance sup- 

 posed to separate the sphere of seventh magnitude stars from 

 the extreme limits of our galaxy. And the great improbability 

 of this view is yet further increased, when it is observed that 

 within this spot there is to bo seen a very marked tendency to 

 the formation of minor streams, around which the milky light 

 seems to cling. It seems, therefore, wholly improbable that 

 the cluster really has that indefinite longitudinal extension 

 suggested by Professor Nichol ; I think, therefore, that the 



