DISSOLUTION. 545 



glomerations, not, indeed, of single stars only, but of single 

 stars, of clusters regular and irregular, of nebulse, and of dif- 

 fused nebulosity. That these have been formed by mutual 

 gravitation of parts once widely scattered, there is evidence 

 in the barrenness of the surrounding celestial spaces: the 

 nubecula minor, especially, being seated, as Humboldt says, 

 in " a kind of starless desert." 



What must be the limit of such concentrations? The 

 mutual attraction of two stars, when it so far predominates 

 over other attractions as to cause approximation, almost 

 certainly ends in the formation of a binary star; since the 

 motions generated by other attractions prevent the two 

 stars from moving in straight lines to their common centre 

 of gravity. Between small clusters, too, having also certain 

 proper motions as clusters, mutual attraction may lead, not 

 to complete union, but to the formation of binary clusters. 

 As the process continues, however, and the clusters become 

 larger, they must move more directly towards each other: 

 thus forming clusters of increasing density. While, there- 

 fore, during the earlier stages of concentration, the proba- 

 bilities are immense against the actual contact of these 

 mutually-gravitating masses; it is tolerably manifest that, 

 as the concentration increases, collision must become proba- 

 ble, and ultimately certain. This is an inference not lack- 

 ing the support of high authority. Sir John Herschel, 

 treating of those numerous and variously-aggregated clus- 

 ters of stars revealed by the telescope, and citing with 

 apparent approval his father's opinion, that the more dif- 

 fused and irregular of these, are " globular clusters in a less 

 advanced state of condensation; " subsequently remarks, 

 that " among a crowd of solid bodies of whatever size, ani- 

 mated by independent and partially opposing impulses, mo- 

 tions opposite to each other must produce collision, destruc- 

 tion of velocity, and subsidence or near approach towards 

 the centre of preponderant attraction; while those which 

 conspire, or which remain outstanding after such conflicts, 



