43] ROYAL ASTRONOMICAL SOCIETY TO ME HIND. 323 



The existence of such a numerous group of small planets in the same 

 part of our system has naturally given rise to much speculation respecting 

 their origin and mutual relations. When, instead of the single planet which 

 was expected to fill up the gap between the orbits of Mars and Jupiter, 

 Ceres and Pallas were found at very nearly the same mean distance from 

 the sun, Olbers threw out the conjecture that they were fragments of a 

 larger planet which had been rent asunder by some internal convulsion, 

 and that many more such fragments probably existed. If this were the 

 case, he reasoned, they would all, after longer or shorter periods, again pass 

 through the point where the explosion took place, and though the pertur- 

 bations which they would suffer, would, in the course of time, prevent them 

 from continuing to pass exactly through the same point, yet it might be 

 expected that they would not stray far from it, and that, therefore, the 

 remaining fragments might be found by carefully watching the parts of the 

 heavens corresponding to the two points in which the orbits of Ceres and 

 Pallas approached towards intersecting. 



Although the finding of Juno and Vesta appeared to give some counte- 

 nance to this hypothesis, later discoveries have deprived it of much of 

 its plausibility. Several of the orbits are everywhere far distant from each 

 other, and where the contrary is the case, the points of nearest approach 

 occur in various parts of the heavens. Probably one reason why Olbers 

 did not discover more of these bodies, though he continued his examination 

 for many years after detecting Vesta, was, that he was induced by his 

 theory to confine the search within too narrow limits. 



Several astronomers have endeavoured to find some general relations 

 between the orbits of this group, similar to that imagined by Olbers ; but 

 it appears to me that they have only succeeded in shewing a kind of 

 general resemblance, indicating rather that similar causes have operated in 

 determining the orbits of these bodies than that they were originally identical. 



If we allow ourselves to speculate on the formation of our planetary 

 system, and adopt the nebular theory, it seems at least as easy to imagine 

 that the nebulous matter, circulating in any particular region about the 

 Sun, would, in cooling, collect into many small masses, as that it would all 

 coalesce into one. 



Although, as has been stated, there is no single point through which 

 all the orbits nearly pass, yet many of them, taken two and two, approach 

 very closely to each other. In the case of Astrcea and Hygeia, in particular, 



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