Clusters of Stars and Nebulce. 57 



tinct impression that they are all nearly at an equal distance 

 from us ; the same is the case with the seven of the Great Bear, 

 and especially with the little constellation Delphinus, easily 

 recognized during the evenings of the present season at some 

 height in the southern sky, to the left of the brilliant Al Tair. 

 No principle of perspective could be reasonably called in to 

 account for the aggregation of so many stars of nearly similar 

 magnitude within so small an area. Other instances might be 

 given of groups, as such associations of stars may be properly 

 called, visible to the naked eye ; but it is in the expanded range 

 of the telescope that they become more universally apparent. 

 There we shall frequently meet with fields characterized by the 

 prevalence of stars of a certain size, and where the evidence of 

 actual vicinity, and oftentimes of very remarkable arrange- 

 ment, is too obvious to be overlooked. These " groups," 

 however, — adopting the accurate classification of Sir W. 

 Herschel, who thus designates compressed collections of stars 

 without central condensation, but forming insulated systems, 

 — present only the simplest form of combination. In the con- 

 tinuance of our researches, and especially if we progressively 

 increase the light of our telescopes, so as to penetrate further 

 into the depth of the heavens, we shall discover a regular 

 series of these aggregations. Groups will come into view not 

 only more rich in numbers, but more thronged by the real or 

 apparent nearness of their individual components; we shall 

 not only notice a tendency to condensation towards the centre 

 of the mass, which may be, though to a very limited extent, 

 the effect of perspective from the greater length of the central 

 visual line, but we shall find, in many instances, a degree of 

 internal compression which perspective is inadequate to explain; 

 and thus we shall be obliged to infer a degree of mutual 

 proximity in that region which we have no means of estima- 

 ting, but which, upon any supposition, must lead to thoughts 

 of wonder as to the general structure of the mass. Such an 

 assemblage, if its general outline were circular, as is frequently 

 the case, would no longer be denominated a "group," but a 

 "globular cluster," "clusters" being, according to Sir W. 

 Herschel's definition, groups so arranged as to indicate the 

 existence of a central force. To many of these most interest- 

 ing objects we hope to direct our readers. 



But we shall soon find that we are, practically at least, 

 dealing with infinitude. Some of these clusters will exhibit 

 their component stars with little difficulty in an ordinary tele- 

 scope ; in others, from the minuteness or the compression of 

 their members — a natural result in either case of increased 

 distance — we shall obtain a less perfect picture, and the general 

 mass will assume a hazy aspect, though its real character will 



