Mr Blackader's Account of an Aurora Borealis. 343 



formed, were still lower, and nearer to the observer. A power- 

 ful beam, from one of these more advanced figures, traversed 

 the arch, and formed a marked contrast, in point of intensity, 

 at the point of bisection. The circular, or crescent-shaped 

 figures, in which the spears of light were often arranged, occu- 

 pied planes, sometimes inclined to the right, which evidently 

 traversed the line of vision ; their nearest, and always broader, 

 margin, being apparently depressed a number of degrees below 

 it ; otherwise, that broader and brighter margin must have 

 covered the farther half; unless, indeed, the nearest were the 

 more elevated ; which, however, could not be the case, unless by 

 great ocular deception. Had they occupied the same plane, the 

 laws of perspective would have placed them in the reverse, in 

 point of apparent elevation. See sketch, Plate IV. No. 9>. 



In general, the principal arch was never obliterated during 

 the greater part of an hour; and although, at first view, it 

 seemed to be composed of a stratum of continuous brilliant light ; 

 yet^ upon subsequent observation, small portions were projected 

 beyond the common line, with encroachments, also, on the infe- 

 rior margin. At times, this became more apparent, with re-en- 

 tering angles. Suddenly a great portion of the arch would break 

 up, forming circular and curved figures, the bases of immense 

 tubular fasciculi, which soon vanished, instantaneously; to be 

 again reconstructed, and to undergo new transformations. 



About 10 p. M. the whole disappeared ; the arch having pre- 

 viously reoccupied the original position, above the star ; and it 

 never retreated farther towards NW. Nor was it followed with 

 any luminous appearanee, gradually retreating below the hori- 

 zon, in that direction, with decreasing brightness ; which is com- 

 monly the case. At this period, a few scattered clouds, pro- 

 ceeding rapidly from SW., had already crossed the magnetic 

 meridian, near the horizon, although the south wind had not 

 yet been perceived at the surface of the earth. Next day it stood 

 in that quarter, bringing a great body of the turgid cloud, pe- 

 culiarly dense, compacted, and low ; and the former tempestuous 

 weather again ensued. 



It may here be remarked, that, on the 16th, the stormy wea- 

 ther had been much felt on the coast of Ayrshire, proceeding 

 from NW., followed with a severe storm of thunder and light- 

 ning. 



