ATJROBA BOEEALIS. 191 



northern light, which encircles the summit of the heavenly 

 canopy with a milder radiance and unflickering emanations of 

 light. It is only in rare instances that a perfect crown or 

 circle is formed, but on its completion the phenomenon has 

 invariably reached its maximum and the radiations become less 

 frequent, shorter, and more colourless. The crown and the lu- 

 minous arches break up, and the whole vault of heaven becomes 

 covered with irregularly scattered, broad, faint, almost ashy 

 gray luminous immovable patches, which in their turn dis- 

 appear, leaving nothing but a trace of the dark, smoke-like 

 -segment on the horizon. There often remains nothing of 

 the whole spectacle but a white, delicate cloud with feathery 

 edges, or divided at equal distances into small roundish 

 groups, like cirro-cumuli. 



This connection of the polar light with the most delicate 

 cirrous clouds deserves special attention, because it shows that 

 'the electro-magnetic evolution of light is a part of a meteoro- 

 logical process. Terrestrial magnetism here manifests its 

 influence on the atmosphere and on the condensation of 

 aqueous vapour. 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 Richard- 

 son near the American North Pole, and by Admiral Wrangel 

 on the Siberian 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 recognised 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 



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

 Sea, in the Years 1819-1822, pp. 552 and 597 ; Thienemann, in the 

 Edinburgh Philosophical Journal, vol. xx. p. 3G6 ; Farquharson, in 

 vol. vi. p. 392, of the same journal ; Wrangel, Phys. Beol., B. 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 



