130 COSMOS. 



tral body simultaneously with the diurnal revolution of the 

 latter.* This limitation of the solar atmosphere in its present 

 concentrated condition is especially remarkable when we com- 

 pare the central body of our system with the nucleus of other 

 nebulous stars. Herschel has discovered several, in which the 

 nidi us of the nebulous matter surrounding the star appeared 

 at an angle of 1 50". On the assumption that the parallax is 

 not fully equal to 1", we find that the outermost nebulous 

 layer of such a star must be 150 times further from the cen- 

 tral body than our Earth is from the Sun. If, therefore, the 

 nebulous star were to occupy the place of our Sun, its atmos- 

 phere would not only include the orbit of Uranus, but even 

 extend eight times beyond it.f 



Considering the narrow limitation of the sun's atmosphere, 

 which we have just described, we may with much probability 

 regard the existence of a very compressed annulus of nebulous 

 matter,^; revolving freely in space between the orbits of Venus 



1549, and embracing a notice of different natural phenomena, epochs of 

 earthquakes and comets (as, for instance, those of 1490 and 1529), and of 

 , (which are important in relation to Mexican chronology,) solar eclipses. 

 In Camargo's manuscript Historia de Tlascala, the light rising in the 

 east almost to the zenith is, singularly enough, described as " sparkling, 

 and as if sown with stars." The description of this phenomenon, which 

 lasted forty days, cannot in any way apply to volcanic eruptions of Popo- 

 catepetl, which lies very near, in the south-eastern direction. (Prescott, 

 History of the Conquest of Mexico, vol. i. p. 284.) Later commentators 

 have confounded this phenomenon, which Montezuma regarded as a warn- 

 ing of his misfortunes, with the " estrella que humeava" (literally, which 

 spring forth \ Mexican choloa, to leap or spring forth). With respect to 

 the connexion of this vapour with the star Citlal Choloha (Venus) aud 

 with " the mountain of the star" (Citlaltepetl, the volcano of Orizaba), see 

 my Monumens, t. ii. p. 303. 



* Laplace, Expos, du Syst. du Monde, p. 270 ; MScanique C6leste, 

 t. ii. pp. 169 and 171 ; Schubert, Astr., bd. iii. . 206. 



t Arago, in the Annuaire, 1842, p. 408. Compare Sir John Her. 

 schel's considerations on the volume and faintness of light of planetary 

 nebulae, in Mary Somerville's Connexion of the Physical Sciences, 1835, 

 p. 108. The opinion that the Sun is a nebulous star, whose atmosphere 

 presents the phenomenon of zodiacal light, did not originate with Domin- 

 icus Cassini, but was first promulgated by Mairan in 1730 (Traiti de 

 I'Aurore Bor., p. 47 and 263 ; Arago, in the Annuaire, 1842, p. 412). 

 It is a renewal of Kepler's views. 



J Dominicus Cassini was the first to assume, as aid subsequently 

 Laplace, Schubert, and Poisson, the hypothesis of a separate ring to 

 explain the form of the zodiacal light. He says distinctly, " If the orbit* 



