THE PLANETS. 463 



rapidity, that the topography of the solar regions appears 

 after the lapse of a few years, quite as antiquated as statistical 

 descriptions of countries. 



Of the 21 satellites now known, 1 belongs to the Earth, 

 4 to Jupiter, 8 to Saturn (the last discovered of these 8 is, 

 according to distance, the seventh, Hyperion; discovered in 

 two different places at the same time by Bond and Lasscll), 

 6 to Uranus (of which the second and fourth are most posi- 

 tively determined), and 2 to Neptune. 



The satellites revolving round the principal planets consti- 

 tute subordinate systems, in which the principal planets take 

 the place of central bodies, forming individual regions of 

 very different dimensions, in which the great solar region is, 

 as it were, repeated in miniature. According to our present 

 knowledge, the region of Jupiter is 2,080,000 geographical 

 miles in diameter, and that of Saturn 4,200,000. In Galileo's 

 time, when the expression of a small Jovial world (Mundus 

 Jovialis) was frequently made use of, these analogies between 

 the subordinate systems and the solar system, contributed 

 much to the more rapid and general diffusion of the Coper- 

 nican system of the world. They suggest the repetitions of 

 form and position which is so frequently presented by organic 

 nature in subordinate spheres. 



The distribution of the satellites in the solar regions is so 

 unequal, that while the , proportion of the moonless principal 

 planets, to those which are accompanied by Moons, is as 

 3 to 5, the latter belong, with the single exception of one, 

 the Earth, to the exterior planetary groups, situated beyond 

 the ring of the asteroids with interlacing orbits. The only 

 satellite which has been formed in the group of interior 

 planets between the Sun and the asteroids, the Earth's Moon, 

 has a remarkably large diameter in proportion to that of its 

 primary. This proportion is -^.-g : while the largest of Saturn's 

 satellites (the sixth. Titan), is perhaps only y^y; and the 



