THE MOON. 485 



by their passage through the atmosphere, and thrown into 

 the shadow cone. The reddened or glowing disc is moreover 

 never uniformly coloured. Some places always appear 

 darker, and are at the same time continually changing colour. 

 The Greeks had formed a peculiar and curious theory with 

 respect to the different colours which the eclipsed Moon wa* 

 said to present according to the hour at which the eclipse 

 took place. 89 



shadow, always predominated, and was indeed alone sensible. 

 It was the more red or orange, in proportion as it was nearer 

 to the geometrical .centre of the shadow ; for those rays 

 which are least refrangible are those which are propagated 

 most abundantly by diffraction, in proportion as they differ 

 from a rectilinear course." The phenomena of diffraction 

 take place as well in a vacuum, according to the acute inves- 

 tigations of Magnus (on the occasion of a discussion between 

 Airy and Faraday). Compare, in reference to the explana- 

 tions by diffraction in general, Arago in the Annuaire for 

 1846, p. 452-455. 



29 Plutarch (De Facie in orbe Lunce), Moral, ed. Wytten. 

 torn. iv. p. 780783 : " The fiery, charcoal-like glimmering 

 (dvOpaKoeirj<i) colour of the eclipsed Moon (about the mid- 

 night hour) is, *as the mathematicians affirm, owing to the 

 change from black into red and bluish, and is by no means to 

 be considered as a character peculiar to the earthy surface of 

 the planet." Also Dio Cassius (Ix. 26, ed. Sturz, p. iii. 

 p. 779), who occupied himself especially with eclipses of the 

 Moon, and the remarkable edicts of the Emperor Claudius, 

 which predicted the dimensions of the eclipsed portion, directs 

 attention to the very different colours which the Moon 

 assumed during the conjunction. He says, (Ixv. 11, torn. iv. 

 p. 185, Sturtz,) "Great was the excitement in the camp of 

 Vitellus. in consequence of the eclipse which took place that 

 night. The mind was filled with melancholy apprehensions, 

 not so much at the eclipse itself, although that might appear 

 to predict misfortune to an unquiet mind, but much more 

 from the circumstance that the Moon displayed blood-red, 

 black, and other gloomy colours." 



o 2 



