THE PLANLfS. Ill 



CGiiraged KepL'r to extend his hypothesis even so far j.s the 

 region of fixed stars. ^ The circumstance which, on the oc- 

 casion of the discovery of Ceres, and the other so-called small 

 jjlanets, first forcibly recalled to mind Kepler's Pythagorean 

 arguments, was his almost forgotten conjecture as to the prob- 

 able existence of a yet unseen 'planet in the great planetles^ 

 chasm beiiceen Mars and Jupiter. (" Motus semper distan- 

 tiam pone sequi videtur ; atque nbi magnus hiatus erat inter 

 orbes, erat et inter motus." f) " I have become more daring," 

 he says, in the introduction to the Mysterimn Cosmograp)h- 

 icum, " and place a new planet between Jupiter and Mars, 

 as also (a conjecture which was less fortunate, arid remained 

 long unnoticedl) another planet between Venus and Mercu- 

 ry ; neither of these have been seen, probably on account of 

 their extreme smallness.§ Kepler subsequently found that 



* Tycho bad denied the existence of the crystalline spheres, in which 

 the planets were supposed to be fixed. Kepler praised the undertak- 

 ing, but he still adhered to the opinion that the sphere of fixed stars 

 was a solid globular shell of two German miles in thickness, upon which 

 are the twelve fixed stars, which are all situated at equal distances from 

 us, and have a peculiar relation to the corners of an icosahedron. The 

 ilxed stars " luniiua sua ab iyihis emittunt ;" " emit light from their own 

 bodies;" he also considered for a long time that the planets were self- 

 luminous, until Galileo taught him better! Although he, like many 

 other of the ancients and Giordano Bruno, considered the fixed stars to 

 be suns like our own, still he was not much inclined to entertain the 

 opinion, which he had well considered, that all fixed stars are sur- 

 rounded by planets, as I had formei'ly stated them to be. (Cosmos, vol. 

 ii., p. 328.) Compare Apelt, Commentary to the Harmonice, p. 21-24 



t [" There seems to be always a close relation between the motion 

 and the distance [of the planets]; that is to say, where there is a great 

 interval between theii' orbs, the same exists also between their mo- 

 tions."] 



X It was not until the year 1821 that Delambre, in the Hist, de V As- 

 tron. Mod., torn, i., p. 314, directed attention to the planets which Kep- 

 ler conjectured to lie between Mercury and Venus, in the extracts 

 which are complete with regard to astronomy, but not with regard to 

 astrology, from Kepler's collected works (p. i314-615). "On n'a fait 

 aucune attention k cette supposition de Kepler, quand on a forme des 

 projets de decouvrir la planete qui (selon une autre de ces predic- 

 tions) devait circuler entre Mars et Jupiter.", " No attention was paid 

 to that supposition of Kepler's when projects were formed for discover- 

 ing the planet, which (according to anotlier of his predictions) ought to 

 revolve between Mars and Jupiter." 



$ The remarkable passage respecting a space to be filled up between 

 Mars and Jupiter [hiatus] is in Ke\)\ev'& Prodromvs Dissertationum Cos- 

 mographicarum, cont'mens Mi/sterinm Cosmo graphicum de admirabili 

 proportione Orbium Coelestium, 1596, p. '': "Cum igitur hac non siicce- 

 deret, alia via, mirum quam audaci, ten^avi aditum. Inter Jovem et 

 Martem interposui novum planetam, ilem')ue alium inter Venerem ci 



