THE AURORA BOREALIS 207 



arch, blended with black rays similar to thick smoke, or 

 simultaneously in many opposite points of the horizon, 

 uniting together to form a flickering sea of flame, whose 

 brilliant beauty admits of no adequate description, as the 

 luminous waves are every moment assuming new and 

 varying forms. Round the point in the vault of heaven 

 which corresponds to the direction of the inclination of 

 the needle, the beams unite together to form the corona 

 the crown of the 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 luminous 

 arches break up, and the whole vault of heaven becomes 

 covered with irregularly scattered broad, faint, almost 

 ashy grey, luminous, immovable patches, which in their 

 turn disappear, 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/ 



These phenomena are also visible in the Southern 

 hemisphere, and are produced by the Aurora Australis. 



The luminous arches were also well described by Mr. 

 William Key in a letter to Dr. Priestley, published in the 

 Philosophical Transactions for 1783. He noticed that 

 the summit of the arch passed near or through the pole- 

 star; the arches were not always accompanied by the 

 ' dancers.' Key, following Canton unwittingly, connected 

 the aurora with discharges of electricity through rarefied 

 gases. His words are: 'Let me hazard a conjecture 

 respecting the white colour and stationary appearance of 

 some of these arches. Experiments in electricity, made 



