12G COSMOS. 



tal vault shattered by it in its fall Kepler, from his ccn 

 Eiderations of comets which intersect the orbits of all the 

 planets,^ boasted, nearly two hundred and fifty years ago, 

 that he had destroyed the seventy-seven concentric spheres 

 of the celebrated Girolamo Fracastoro, as well as all tlsr- 

 more ancient retrograde epicycles. The ideas entertaineu 

 by such great thinkers as Eudoxus, Mencschmus, Aristotle, 

 and Apollonius Pergseus, respecting the possible mechanism 

 and motion of these solid, mutually intersecting spheres by 

 which the planets were moved, and the question whether 

 they regarded these systems of rings as mere ideal modes of 

 representation, or intellectual fancies, by means of which diffi- 

 cult problems of the planetary orbits might be solved or de- 

 termined approximately, are subjects of which I have already 

 treated in another place,! and which are not devoid of interest 

 in our endeavors to distinguish the difierent periods of devel- 

 opment which have characterized the history of astronomy. 

 Before we pass from the very ancient, but artificial zodi- 

 acal grouping of the fixed stars, as regards their supposed 

 insertion into solid spheres, to their natural and actual ar- 

 rangement, and to the known laws of their relative distri- 

 bution, it will be necessary more fully to consider some of 

 the sensuous phenomena of the individual cosmical bodies — 

 their extending rays, their apparent, spurious disk, and their 

 differences of color. In the note referring to the invisibility 

 of Jupiter's satellites,! I have already spoken of the influ- 

 ence of the so-called tails of the stars, which vary in num- 

 ber, position, and length in difierent individuals. Indistinct- 

 ness of vision {la vue inclhtincte) arises from numerous or- 

 ganic causes, depending on aberration of the sphericity of 



* Kepler expressly says, in his Stella Martis, ful. 9 : " Solidos orbes 

 rejeci." ''I have rejected the idea of solid orbs;" and in the Stella 

 Nova, IGOfi, cap. 2, p. 8 : '■' Planetse in puro selhere, periude atque 

 aves in acre cursus sues conficiunt." " The planets perform their 

 course in the pure ether as birds pass through the air." Compare also 

 p. 1*2'2. lie inclined, however, at an earlier period, to the idea of a 

 eolid icy vault of heaven congealed from the absence of solar heat: 

 • Orbis ex aqua factus gelu concreta propter solis absentiam." (Kepler, 

 F.pit. Astr. Copern., i., 2, p. 51.) "Two thousand years before Kepler, 

 Empedocles maintained that the fixed stars were riveted to the crystal 

 heavens, but that the planets were free and unrestrained" {rovq 6e TzXav- 

 Tjrac avfladai). (Pint., plac. Phil., ii., 13; Emped., 1, p. 335, Sturz; 

 Euseb., Prcpp. Evang., xv., 30, col. 1688, p. 839.) It is difficult to con- 

 ceive how, according to Plato in the Tira;.eus ( Tim., p. 40, B ; see Bohn'g 

 edition cf Plato, vol. ii., p. 344; but not according to Aristotle), the fixed 

 Btars, riveted as they are to solid spheres, could rotate independently, 

 ■* Cosr^ns, vol. ii., p 31o, 316. + Vide supra, p. 51, and note. 



