PLANETARY SYSTEMS. 9(» 



known conditions, aJthough man considers as accidental what' 

 ever he is unable to explain in the planetary formation on pure- 

 ly genetic principles. If the planets have been formed out of 

 separate rings of vaporous matter revolving round the Sun, 

 we may conjecture that the different thickness, unequal dens- 

 ity, temperature, and electro-magnetic tension of these rings 

 may have given occasion to the most various agglomerations 

 of matter, in the same manner as the amount of tangential 

 velocity and small variations in its direction have produced so 

 great a difference in the forms and inclinations of the elliptic 

 orbits. Attractions of mass and laws of gravitation have no 

 doubt exercised an influence here, no less than in the geog- 

 nostic relations of the elevations of continents ; but we are un- 

 able from present forms to draw any conclusions regarding the 

 series of conditions through which they have passed. Even 

 the so-called law of the distances of the j)lanets from the Sun, 

 the law of progression (which led Kepler to conjecture the ex- 

 istence of a planet supplying the link that was wanting in the 

 chain of connection between Mars and Jupiter), has been found 

 numerically inexact for the distances between Mercury, Venus, 

 and the Earth, and at variance with the conception of a series, 

 owing to the necessity for a supposition in the case of the first 

 member. 



The hitherto discovered principal planets that revolve roun(? 

 our Sun are attended certainly by fourteen, and probably by 

 eighteen secondary planets (moons or satellites). The princi- 

 pal planets are, therefore, themselves the central bodies of sub- 

 ordinate systems. We seem to recognize in the fabric of thf 

 universe the same process of arrangement so frequently ex- 

 hibited in the development of organic life, where we find in 

 the manifold combinations of groups of plants or animals the 

 same typical form repeated in the subordinate classes. Tho 

 secondary planets or satellites are more frequent in the extern- 

 al region of the planetary system, lying beyond the intersect- 

 ing orbits of the smaller planets or asteroids ; in the inner re- 

 gion none of the planets are attended by satellites, with the 

 exception of the Earth, whose moon is relatively of great mag- 

 nitude, since its diameter is equal to a fourth of that of the 

 Earth, while the diameter of the largest of all known second 

 ary planets — the sixth satellite of Saturn — is probably abou\ 

 one seventeenth, and the largest of Jupiter's moons, the third, 

 only about one twenty-sixth part that of the primary planet 

 or central body. The planets which are attended by tne 

 largest number of satellites are most remote from the Surv 



