XVI NOTES. 



S. 47 49, and in the Astronomische Nachrichten, Bd. xvii. S. 401, 402; 

 menu error 0"0141. Respecting the relative distances of stars of different 

 magnitudes, how those of the third magnitude may probably be three times 

 more distant, and in what manner we may represent to ourselves the arrange- 

 ment of the sidereal strata, I find in Kepler's Epitome Astronomise Coperni- 

 canee, 1618, T. i. Lib. i. p. 34 39, a remarkable passage : " Sol hie noster 

 nil aliud est quam una ex fixis, nobis major et clarior visa, quia proprior quara 

 fixa. Pone terrain stare ad latus, uno semidiametro vise lactese, tune hecc 

 via lactea apparebit circulus parvus, vel ellipsis parva, tota declinans ad latus 

 alterum; eritque simul uno intuitu conspicua, quae nunc non potest nisi 

 dimidia conspici quovis momento. Itaque fixarum sphsera non tantum orbe 

 stellarum, sed etiam circulo lactis versus nos deorsum est termiuata." 



( A5 ) p. 82. " Si dans les zones abandonnees par 1'atmosphere du soleil il 

 s'est trouve des molecules trop volatiles pour s'unir entre elles ou aux planetes, 

 dies doivent en continuant de circuler autour de cet astre, offrir toutes les ap- 

 parences de la lumiere zodiacale, sans opposer de resistance sensible aux divers 

 corps du systeme planetaire, soit a cause de leur extreme rarete, soit parceque 

 leur mouvement est a fort peu pres le meme que celui des planetes qu'elles 

 rencontrent." Laplace, Exp. du Syst. du Monde (ed. 5), p. 415. 



(S 6 ) p. 82. Laplace, Exp. du Syst. du Monde (ed. 5), pp. 396 and 414. 



(37) p. 82. Littrow's Astronornie, 1825, Bd. ii. S. 107. Madler, Astr. 

 1841, S. 212. Laplace, Exposition du Systeme du Monde, p. 210. 



(S 3 ) p. 84. Kepler on the increasing volume and density of the planets 

 with the increase of their distance from the sun or central body, itself de- 

 scribed as the densest of all the heavenly bodies (Epitome Astron. Copern. in 

 vii. libros digesta, 1618 1622, p. 420). Leibnitz was also inclined to the 

 opinion of Kepler and Otto von Guericke, . e. that the planets increase in 

 volume in proportion to their distance from the sun. See his letter to the 

 Magdeburg Burgomaster (Mainz, 1671), in Leibnitz, deutschen Schriften, 

 heraosg. von Guhrauer, Th. i. S. 264. 



P) p. 84. For a tabular statement of the masses, see Encke, in Schu- 

 macher's Astr. Nachr. 1843, No. 488, p. 114. 



(*) p. 87. Taking the semi-diameter of the moon at 0.2725, according to 

 Burckhardt's determination, and its volume at ^ , its density is found 

 0.5596, or nearly. Compare also Wilhelm Beer and H. Miidler, der 

 Mond, S. 2 und 10, as well as Madler, Astr. S. 157. The material contents 

 are, according to Hansen, nearly -fa, and according to Madler, of those 

 of the earth, 4uid its mass -- of that of the earth. In the largest of 



