XCU NOTES, 



est causee par la vivacite" de la blancheur de la voie lactee qui renferme 1'espace 

 noir et 1'entoure de tous cotes." Lacaille, in the Mem. de 1'Acad. des Sci- 

 ences, annee 1755 (Paris, 1761), p. 199. 



(**) p. 257. Bd. i. S. 159 and 415 (Anm. 87) ; Eng. ed. p. 143 and 

 xxxviii. Note 117. 



O 68 ) p. 257." When we see," says Sir John Herschel, " in the Coal sack 

 (near a Crucis) a sharply-defined oval space free from stars, it would seem 

 much less probable that a conical or tubular hollow traverses the whole of a 

 starry stratum, continuously extended from the eye outwards, than that -a 

 distant mass of comparatively moderate thickness should be simply perfo- 

 rated from side to side. ..." (Outlines, 792, p. 532 ; Lettre de Mr. 

 Hooke a Mr. Auzout, in the Mem. de 1' Academic, 1666-1699, T. viii. Partie 

 2, p. 30 and 73). 



(0 p. 258. Kosmos, Bd. i. S. 161 ; Eng. ed. p. 145. 



( 46 ) p. 261. Compare what was said in an earlier volume, where dis- 

 tances of Uranus were employed as units of measure, that planet beiug the 

 outermost member of the planetary system as then known to us (Kosmos 

 Bd. i. S. 116, 153, and 415, Anm. 76 ; Eng. ed. p. 102, 103, 137, 138. 

 and Note 106). Taking the distance of Neptune from the Sun at 30'04 

 distances of the Earth from the Sun, the distance of a Centauri from the 

 Sun will be 7523 distances of Neptune, the parallax of the star being assumed 

 to be 0".9128 (Kosmos, Bd. iii. S. 274, Eng. ed. p. 189) ; and yet the dis- 

 tance of 61 Cygni is almost twice and a half, and that of Sirius (taking its 

 parallax at 0"'230) four times as great as that of o Centauri. A " distance 

 of Neptune" is about 621 German, (2484 English) millions of geographical 

 miles ; and the distance of Uranus from the Sun, according to Hanseu, is 

 396 (Eng. 1586) millions of such miles. According to Galle, the distance 

 of Sirius, taking Henderson's parallax, is 896800 semi-diameters of the 

 Earth's orbit =18547000 (74188000 Eng.) millions of geographical miles 

 a distance which light requires 14 years to traverse. The aphelion of the 

 comet of 1680 is 44 distances of Uranus, or 28 distances of Neptune, from 

 the Sun. According to the above assumptions, the solar distance of the star 

 o Centauri is almost 270 times greater than this cometary aphelion, which is 

 here regarded as the minimum of the necessarily very uncertain estimation of 

 the radius of the solar domain (Kosmos, Bd. iii. S. 294, Eng. ed. p. 204). In 



