THE PLANETS. Ill 



couraged Kepler to extend his hypothesis even so far as the 

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

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

 planets, 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 planetless 

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

 tiam pone sequi videtur ; atque ubi magnus hiatus erat inter 

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

 he says, in the introduction to the Mysterium Cosmograph- 

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

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

 long unnoticed!) 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 had 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 

 fixed stars " lamina sua ab intus 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 formerly 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 tb^re is a great 

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

 tions."] 



t It was not until the year 1821 that Delambre, in the Hist, de VAs- 

 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. 314-615). "On n'a fait 

 aucune attention a 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 another of his predictions) ought to 

 revolve between Mars and Jupiter." 



The remarkable passage respecting a space to be filled up between 

 Mai's and Jupiter [hiatus] is in Kepler's Prodromus Dissertalionum Cos- 

 mographicarum, continens Mysterium Cosmograpkicum de admirabili . 

 proportionc Orbium Ccelestium, 1596, p. 7 : "Cum igitur hac non succe- 

 deret, alia via, mirum quam audaci, tentavi aditum. Inter Jovem et 

 Martem interposui novum planetam, itemque alium inter Venerem et 



