192 COSMOS. 



converging polar zones (streaks of clouds in the direction of 

 the magnetic meridian), which constantly occupied my atten- 

 tion during my journeys on the elevated plateaux of Mexico, 

 and in Northern Asia, belong probably to the same group 

 of diurnal phenomena.* 



Southern lights have often been seen in England by the 

 intelligent and indefatigable observer Dalton, and northern 

 lights have been observed in the southern hemisphere as far 

 as 45 latitude (as on the 14th of January, 1831). On occasions 

 that are by no means of rare occurrence, the equilibrium at 

 both poles has been simultaneously disturbed. I have disco- 

 vered with certainty that northern polar lights have been seen 

 within the tropics in Mexico and Peru. We must distinguish 

 between the sphere of simultaneous visibility of the pheno- 

 menon and the zones of the earth where it is seen almost 



of September, 1827. A luminous arch, 20 high, with columns pro- 

 ceeding from it, was seen at noon in a part of the sky that had been 

 clear after rain. (Journal of the Royal Institution of Great Britain, 

 1828, Jan., p. 429.) 



* On my return from my American travels, I described the delicate 

 cirro-cumulus cloud, which appears uniformly divided, as if by the action 

 of repulsive forces, under the name of polar bands (bandes polaires), 

 because their perspective point of convergence is mostly at first in 

 the magnetic pole, so that the parallel rows of fleecy clouds follow the 

 magnetic meridian. One peculiarity of this mysterious phenomenon is 

 the oscillation, or occasionally the gradually progressive motion, of the 

 point of convergence. It is usually observed that the bands are only 

 fully developed in one region of the heavens, and they are seen to move 

 first from south to north, and then gradually from east to west. I could 

 not trace any connection between the advancing motion of the bands 

 and alterations of the currents of air in the higher regions of the atmo- 

 sphere. They occur when the air is extremely calm and the heavens are 

 quite serene, and are much more common under the tropics than in the 

 temperate and frigid zones. I have seen this phenomenon on the Andes, 

 almost under the equator, at an elevation of 15,920 feet, and in Northern 

 Asia, in the plains of Krasnojarski, south of Buchtarminsk, so similarly 

 developed, that we must regard the influences producing it as very 

 widely distributed, and as depending on general natural forces. See 

 the important observations of Kiimtz ( Vorlesungen uber Meteorologie, 

 1840, s. 146), and the more recent ones of Martins and Bravais (Me- 

 teorologie, 1843, p. 117). In south polar bands, composed of very 

 delicate clouds, observed by Arago at Paris on the 23rd of June, 1844, 

 dark rays shot upwards from an arch running east and west. We have 

 already made mention of black rays resembling dark smoke, as occur- 

 ring in brilliant nocturnal northern lights. 





