436 COSMOS. 



of these have been seen, probably on account of their extreme 

 smalluess. 27 Kepler subsequently found that he did not 

 require these new planets for his solar system founded upon 



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 discovering the planet which (according to another 

 of his predictions) ought to revolve between Mars and Jupiter." 

 87 The remarkable passage respecting a space to be rilled 

 up between Mars and Jupiter [hiatus] is in Kepler's Pro- 

 dromus Dissertationum cosmographicarum, continent Mys- 

 terium cosmographicum de admirabili proportione orbium 

 cfrlestium, 1596, p. 7 : " Cum igitur hac non succederet, 

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

 et Martem interposui novum planetam, itemque alium inter 

 Venerem et Mercurium. quos duos forte ob exilitatem non 

 videamus, iisque sua tempora periodica ascripsi. Sic enim 

 existimabam me aliquam cequalitatem proportionum eff'ec- 

 turum, quse proportiones inter binos versus Solem ordine 

 minuerentur, versus fixas augescerent ; ut propior est Terra 

 Veneri quantitate orbis terrestris, quam Mars Terrse, in 

 quantitate orbis Martis. Verum hoc pacto neque unius 

 plauetse interpositio sufficiebat ingenti hiatu, Jovem inter et 

 Martem: manebat enim major Jovis ad ilium novum pro- 

 portio, quain est Saturni ad Jovem. Rursus alio modo 

 exploravi." " When this plan therefore failed, I tried to reach 

 my aim in another way. of, I must confess, singular boldness. 

 Between Jupiter and Mars I interposed a new planet, and 

 another also between Venus and Mercury, both which it is 

 possible are not visible on account of their minuteness, and I 

 assigned to them their respective periods. For in this way 

 I thought that I might in some degree equalize their ratios, 

 which ratios regularly diminished towards the Sun, enlarged 

 towards the fixed stars; as the Earth is nearer to Venus 

 than Mars is to the Earth. But even in this way the inter- 

 position of one planet did not supply the great chasm between 

 Jupiter and Mars, for the ratio between Jupiter and the 

 supposed new planet still remained greater than between 

 Saturn and Jupiter. Again I tried in another way." Kepler 

 was twenty-five years of age when he wrote this. It may 

 be seen how his restless mind formed hypotheses, and again 



