No. Yl,-^District of the Bay of Baja. 101 



*' Deveuere locos laetos, et amoena vireta 



Fortunatorum nemorum, sedesque beatas. 

 "^__ Largior hie campos aether, et lumine vestit 



* " ' Purpureo; solemque suum, sua sidera norunt." 



En. vi. 638. 



The citation of this passage not only illustrates a classical lo- 

 cality, but enables me to make a remark, which I believe is 

 new, upon a physical fact. The " lumen purpureus"" of 

 Virgil has generally been considered as a poetical fiction, and 

 the variorum commentators have considered it merely as an 

 emblem of beauty and purity. I have, however, had occasion 

 to observe in the evening sky at Naples the most exquisitely 

 purpurean tinge, not like the red glow of our sunsets, but 

 pale and intimately invested in the colour of a sky of perfect 

 purity, such as can never be seen in northern climates. The 

 cause too is capable of the most perfectly philosophic explana- 

 tion. The azure of the sky is imputable to the resistance of 

 the atmosphere to the rays of light, by which the red rays, 

 moving with most momentum, pass entirely through, while the 

 blue are absorbed and reflected by the dense medium. The 

 red tints of sunset and sunrise are owing to the accumulation 

 of the atmospheric strata through which the rays must pass, 

 by which not even those having the greatest momentum can 

 escape ; hence also the red light observed by divers under 

 water. But the purple tinge which I observed at Naples even 

 near the zenith, had no affinity with this cause. The atmo- 

 sphere possessing there a surpassing purity, a portion of the 

 blue rays having a free passage, escaped, and a part of the 

 violet, which have least momentum of any, even found their 

 way to the eye, thus producing a tinge which Virgil, himself 

 an admirable observer of nature, transferred to his Elysian 

 skies as a testimony of such habitual purity as was rarely to 

 be observed even under the genial climate of Italy. We may 

 therefore justify the poet even to the letter, and refute the ob- 

 servation of one, who, though no philosopher, was disposed to 

 view things under the colouring of a warm and classical ima- 

 gination, that, " in the splendour of a Neapolitan firmament, 

 we may seek in vain for that purple light so delightf v .c o ir 

 boyish fancy."* 



* Eustace. 



