AURORA ROREALIS. 197 



fluence on the atmosphere and on the condensation of aqueous 

 vapor. The fleecy clouds seen in Iceland by Thienemann, 

 and which he considered to be the northern light, have been 

 seen in recent times by Franklin and Richardson near the 

 American north pole, and by Admiral Wrangel on the Sibe- 

 rian coast of the Polar Sea. All remarked " that the Aurora 

 flashed forth in the most vivid beams when masses of cirrous 

 strata were hovering in the upper regions of the air, and when 

 these were so thin that their presence could only be recognized 

 by the formation of a halo round the moon." These clouds 

 sometimes range themselves, even by day, in a similar manner 

 to the beams of the Aurora, and then disturb the course of 

 the magnetic needle in the same manner as the latter. On 

 the morning after every distinct nocturnal Aurora, the same 

 superimposed strata of clouds have still been observed that 

 had previously been luminous.* The apparently converging 

 polar zones (streaks of clouds in the direction of the magnetic 

 meridian), which constantly occupied my attention during my 

 journeys on the elevated plateaux of Mexico and in Northern 

 Asia, belong probably to the same group of diurnal phenom- 

 ena. t 



* John Franklin, Narrative of a Journey to the Shores of the Polar 

 Sea, in the Years 1819-1822, p. 552 and 597 ; Thieuemanu, in the 

 Edinburgh Philosophical Journal, vol. xx., p. 336 ; Farquharson, in vol. 

 vi., p. 392, of the same jouvnal ; Wrangel, Phys. Beob., s. 59. Parry 

 even saw the great arch of the northern light continue throughout the 

 day. {Journal of a Second Voyage, performed in 1821-1823, p. 156.) 

 Something of the same nature was seen in England on the 9th of Sep- 

 tember, 1827. A luminous arch, 20^ high, with columns proceeding 

 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.) 



t On my return from my American ti'avels, I described the delicate 

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

 action of I'epuUive forces, under the name of polar bands {bandes ^w- 

 laires), 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 mystei'ious phenomenoL 

 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 seeu 

 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 

 atmosphere. They occur when tlie 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 phe- 

 nomenon on the Andes, almost under the equator, at an elevation of 

 15.920 feet, and in Northern Asia, \n. the plains of Krasnojarski, south 



