113 COSMOS. 



he did not require these new planets for hi« solar system 

 founded upon the properties of the regular solids ; it was only 

 necessary to modify the distances of the old planets a little 

 arbitrarily. ('' Non reperies novos et incognitos planetas, ut 

 paulo antea, interpositos, non ea mihi probatur audacia ; sed 

 illos veteres parum admodum luocatos''^ — Myst. Cosmogr., 

 p. 10.) The ideal tendencies of Kepler were so analogous 

 to those of the Pythagorean school, and still more to those of 

 Plato expressed in the Timceus,^ that in the same way as 

 Plato [Cratyl., p. 409) assumed, in addition to the difier- 

 ences of tone in the planetary spheres, those of color, Kepler 

 likewise instituted some experiments [Astron. Opt., cap. 6, 

 p. 261) for the purpose of detecting the colors of the planets. 

 Even the great Newton, always so precise in his conclusions, 

 was inclined, as Prevost has already remarked (^Mem. de 

 VAcad. de Berlin for 1802, p. 77 and 93), to reduce the di- 



Mercurium, quos duos forte ob exilitatem non videamus, iisque sua 

 tempora periodica ascripsi. Sic enim existimabam me aliquam aequal- 

 itatem proportioniim effecturum, quae proportiones inter biuos versus 

 Solem ordine minuerentur, versus fixas augescerent ; ut propior est 

 Terra Veneri quantitate ori)is terrestris, quara Mars Terrse, in quanti- 

 tate orbis Martis. Verum hoc pacto neque unius planetiB interpositio 

 sufBciebat ingenti hiatu, Jovem inter et Martem: manebat enim major 

 Jovis ad ilium novum proportio, quam 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 equal- 

 ize their ratios, which ratios regularly diminished toward the Sun, and 

 enlarged toward the fixed stars, as the Earth is nearer to Venus than 

 Mars is to the Earth. , But even in this way the interposition 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 quick- 

 ly forsook them, to deceive himself with others. He always retained 

 a hopeful faith in being able to discover numerical laws where matter 

 had aggregated under the manifold disturbances of attractive forces 

 (disturbances whose combinations are incalculable, as are so many past 

 events and formations on account of our ignorance of the accompanying 

 conditions), aggregated into globes, revolving in orbits, sometimes sim 

 pie and almost parallel, sometimes grouped together and surprisingly 

 complicated. 



* [" You will not find new and unknown planets, as I said before ; 

 that boldness I do not approve of; but you will find the old ones a little 

 altered in position."] 



t {Plato's Wo'ks translated, vol. ii., Bohn'e Classical Libraiy."] 



