f'-XXVlll SOTES. 



( 67 ) p. 355. Kepler, Paralip. vel Astronomise pars Optica, 1604, p. 297. 



( 571 ) P- 356. " On concoit qne la vivacite de la lumiere rouge ne depend 

 pes uniquement de 1'etat de I'atniosphere, qui refracte, plus ou moins affaiblis, 

 les rayons solaires, en les inflechissant dans le cone d'orabre, mais qu'elle est 

 modifiee surtout par la transparence variable de la partie de PatmoEohere a 

 travers laquelle nous apercevons la Lune eclipsee. Sous les tropiques une 

 grand serenite du ciel, une dissemination uniforme des vapeurs, ditninuent 

 ^extinction de la lumiere que le disque lunaire nous renvoie." (Humboldt, 

 Voyage aux Regions equinoxiales, T. iii. p. 544 ; and Recueil d'Observ. astro- 

 iiomiques, Vol. ii. p. 145.) Arago remarks : " Les rayons solaires arrivent 

 a notre satellite par 1'effet d'une refraction et a la suite d'une absorption dans 

 les couches les plus basses de I'atmosphere terrestre ; pourroient-ils avoir une 

 autre teinte que le rouge ?" (Annuaire pour 1842, p. 528.) 



( 572 ) p. 356. Babinet explains the redness as a consequence of diffraction, 

 in a notice on the different portions of white, blue, and red light, produced 

 when there is inflexion. See Babinet's considerations on the total eclipse of 

 the Moon on the 19th of March, 1848, in Moigno's Repertoire d'Optique 

 moderne, 1850, T. iv. p. 1656. "La lumiere diffractee qui penetre dans 

 1'ombre de la terre, predomine toujours et meme a ete seule sensible. Elle 

 est d'autant plus rouge ou orangee qu'elle se trouve plus pres du centre de 

 Pombre geometrique ; car ce sont les rayons les moins refrangibles qui se 

 propagent le plus abondamment par diffraction, a mesure qu'on s'eloigne de 

 la propagation en ligne droite." The phenomena of diffraction take place in 

 vacuo Iso, according to the ingenious investigations of Magnus, on the occa- 

 sion of a discussion between Airy and Faraday. On explanations by diffrac- 

 tion, see, generally, Arago in the Annuaire pour 1846, p. 452 455. 



( 573 ) p. 357. Plutarch (de facie in orbe Lunse), Moral, ed Wyttenb. T.iv. 

 p. 780 783 : " The fiery coal-glowing (cti#paKwei8ijs) colour of the darkened 

 Moon (about the hour of midnight) is, as mathematicians maintain, by no 

 means to be regarded, seeing that the change is from black to red and blueish, 

 as belonging to the earthy surface of that body." Dion Cassius, also (Ix. 26 ; 

 ed Sturz, T. iii. p. 779), who had besides occupied himself in much detail with 

 the subject of lunar eclipses, and with the remarkable edicts of the Emperor 

 Claudius, in which the dimensions of the darkened portion were announced 

 beforehand, calls attention to the great alterations in the colour of the 

 Moon during the conjunction. He says (Ixv. 11 ; T. iv. p. 185, Sturz) : 

 " Great was the confusion created in the camp of Vitellius by the eclipse which 

 took place that night ; yet it was not so much the eclipse itself although to 



