82 CELESTIAL PHENOMENA. 



principal planets. We may, with considerable probability, 

 include within the dominion of our sun, and the immediate 

 sphere of its central force, a rotating ring of finely, 

 divided or nebulous matter, situated, perhaps, between the 

 orbits of Venus and Mars, but certainly extending beyond 

 that of the earth ( 35 ), which is called by us the Zodiacal 

 Light ; and a host of extremely small asteroids, the paths 

 of which intersect, or very nearly approach, that of the 

 Earth, and which present to us the phenomena of aerolites, 

 or shooting stars. When we take into our consideration 

 all the varied forms of bodies which revolve round the sun 

 in more or less eccentric paths, unless we are inclined, with 

 the illustrious author of the " Mecanique Celeste," to view 

 the greater number of comets as nebulous stars, wandering 

 from one central system to another ( 36 ), we must acknow- 

 ledge that the planetary system distinctively so called (i. e. 

 the group of bodies which in only slightly eccentric orbits 

 revolve around the sun, with their attendant moons,) forms, 

 not indeed, in mass, but in number, a comparatively small 

 portion of the entire solar system. 



It has been proposed to consider the telescopic planets, 

 Vesta, Juno, Ceres, and Pallas, with their more eccentric, 

 intersecting, and greatly inclined orbits, as forming a 

 middle zone, or group, in our planetary system ; and if we 

 follow out this view, we shall find that the comparison of 

 the inner group of planets, comprising Mercury, Venus, 

 the Earth, and Mars, with the outer group, consisting of 

 Jupiter, Saturn, and Uranus, presents several striking con* 

 trasts ( 37 ). The planets of the inner group, which are nearer 

 the -sun, are of more moderate size, are denser, rotate around 

 their respective axes more slowly in nearly equal periods 



