NOTES. XXXV 



TlascaX the light rising in the east almost to the zenith, is strangely enougli 

 called " sparkling, and as if thick set with stars." The description of the 

 phsenomenoii, which is said to have lasted forty days, can by no means be 

 understood to apply to volcanic eruptions of the Popocatepetl, which is situated 

 at only a small distance to the south-east. (Prescott, History of the Conquest 

 of Mexico, Vol. i. p. 284). More recent commentators have confounded thia 

 phenomenon, which Montezuma regarded as a presage of misfortune, with the 

 " estrella que humeava" (" which scintillated :" Mexican choloa, to scintillate). 

 Respecting the connection of this vapour with the star Citlal Choloha (the 

 planet Venus) and the " mountain of the star" (Citlaltepetl, the volcano of 

 Orizaba), see my Monumens, T. ii. p. 303. 



H p. 130. Laplace, Exp. du Syst. du Monde, p. 270 ; Me'c. eel. T. ii. 

 p. 169 and 171 ; Schubert, Ast. Vol. iii. 206. 



( M ) p. 130. Arago, Annuaire, 1842, p. 408. Compare Sir John 

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

 nebulae, in Mrs. Somerville's Connexion of the Physical Sciences, 1835, p. 108. 

 The idea of the sun being a nebulous star, whose atmosphere presents the 

 phsenomenon of the zodiacal light, was first started, not by Dominic Cassini, 

 but by Mairan, in 1731 (Traite de 1'Aurore Bor. p. 47 and 263 ; Arago, in 

 the Annuaire, 1842, p. 412). It was a renewal of Kepler's views. 



( % ) pp. 130. Dominic Cassini assumed, as did subsequently Laplace, Schu- 

 bert, and Poisson, the hypothesis of a detached ring, to explain the form of the 

 zodiacal light. He says distinctly : " Si les orbits de Mercure et de Venus 

 etoient visibles (materiellement dans toute 1'etendue de leur surface), nous les 

 verrions habituellement de la meme figure et dans la meme disposition a 

 1'egard du soleil et aux memes terns de 1'annee que la lumiere zodiacale." 

 (Mem. de 1'Acad. T. viii. 1730, p. 218 ; and Biot, in the Comptes-reudus, 

 1836, T. iii. p. 666.) Cassini supposed that the nebulous ring of the 

 zodiacal light consisted of a countless number of small planetary bodies 

 which revolve round the sun. He was inclined to believe that the full of 

 the fire-balls might be connected with the passage of the earth through the 

 zodiacal nebulous ring. Olmsted, and especially Biot, in the above-men- 

 tioned volume of the Comptes-rendus, p. 673, have attempted to connect it 

 with the November fall of aerolites, but Olbers regarded this as very doubtful. 

 (Schum. Jarbuch, 1837, S. 281.) On the question whether the plane of tne 

 zodiacal light coincides perfectly with the plane of the sun's equator, see 

 Houzeau, in Schum. Astr. Nachr. 1843, Nr. 492, S. 190. 



( 9 p. 131 Sir John Herschel, Aatron. 487. 



