126 COSMOS. 



proximate to a certain degree, in their inconsiderable mass 

 and the diversity of their orbits, to comets, they present this 

 essential difference from the latter bodies, that our knowledge 

 of their existence is almost entirely limited to the moment of 

 their destruction, that is, to the period when drawn within 

 the sphere of the earth's attraction, they become luminous 

 and ignite. 



In order to complete our view of all that we have learnt to 

 consider as appertaining to our solar system, which now, since 

 the discovery of the small planets, of the interior comets of 

 short revolutions, and of the meteoric asteroids, is so rich and 

 complicated in its form, it remains for us to speak of the ring 

 of Zodiacal Light, to which we have already alluded. Those 

 who have lived for many years in the zone of palms must retain 

 a pleasing impression of the mild radiance with which the 

 zodiacal light, shooting pyramidally upwards, illumines a part 

 of the uniform length of tropical nights. I have seen it shine 

 with an intensity of light equal to the Milky Way in Sagit- 

 tarius, and that not only in the rare and dry atmosphere of 

 the summits of the Andes at an elevation of from thirteen 

 to fifteen thousand feet, but even on the boundless grassy 

 plains, the Llanos of Venezuela, and on the sea-shore, be- 

 neath the ever clear sky of Cumana. This phenomenon was 

 often rendered especially beautiful by the passage of light 

 fleecy clouds, which stood out in picturesque and bold relief 

 from the luminous background. A notice of this aerial spec- 

 tacle is contained in a passage in my journal, while I was on 

 the voyage from Lima to the western coasts of Mexico : 

 " For three or four nights (between 10 and 14 N. lat.) the 

 zodiacal light has appeared in greater splendour than I have 

 ever observed it. The transparency of the atmosphere must 

 be remarkably great in this part of the Southern Ocean, to 

 judge by the radiance of the stars and nebulous spots. 

 From the 14th to the 19th of March a regular interval of 

 three-quarters of an hour occurred between the disappearance 

 of the sun's disc in the ocean and the first manifestation of 

 the zodiacal light, although the night was already perfectly 

 dark. An hour after sunset it was seen in great brilliancy 

 between Aldebaran and the Pleiades; and on the 18th of 

 March it attained an altitude of 39 5'. Narrow elongated 

 clouds are scattered over the beautiful deep azure of the dis- 



