OPTICAL PHENOMENA. 



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of all the older Residents at the European ports, induced him to believe that its motions 

 are sometimes audible. It has also been debated, what effect the auroral light produced 

 upon the stars in its path, respecting which, Parry states : "Of its dimming the stars 

 there cannot be a doubt ; we remarked it to be in this respect like drawing a gauze yeil 

 over the heavens in that part, the veil being the thickest when two of the luminous sheets 

 met and overlapped." 



Various results of calculation have been given as to the elevation of auroral phe- 

 nomena. They clearly occur within the limits of our atmosphere, from the fact of 

 the earth's diurnal motion having no effect upon the apparent position of the meteor. 

 M. de Mairan assigns to it a mean height of 175 French leagues, equal to 464 English 

 miles ; Dr. Dalton concludes the average elevation to be about 100 English miles ; but 

 according to Parry, the auroral appearances seemed to be .full as near as many of the 

 clouds commonly seen. In one instance, the aurora appeared to be connected with a very 

 remarkable cloud of a light brown colour, resembling an immense volume of smoke, or a 

 powder magazine in a state of explosion, (the comparison of the gunner,) for upon the 

 breaking up of the cloud the phenomenon was seen in the same part of the heavens. The 

 experience of Beechy is in favour of a comparatively low elevation. " We frequently 

 observed," he states, " the aurora attended by a thin, fleecy, cloud-like substance, which, 

 if not part of the meteor, furnishes a proof of the displays having taken place within the 

 region of our atmosphere, as the light was decidedly seen between it and the earth. This 

 was particularly noticed on the 28th of September, 1827. The aurora on that night began 

 by forming two arches from W. by N. northward -to E. by N., and about eleven o'clock 

 threw out brilliant coruscations. Shortly after the zenith was obscured by a lucid haze, 

 which soon condensed into a canopy of light clouds. We could detect the aurora above 

 this canopy by several bright arches being refracted, and by brilliant colours being 

 apparent in the interstices. Shortly afterwards the meteor descended, and exhibited a 

 splendid appearance, without any interruption from clouds, and then retired, leaving the 

 fleecy stratum only visible at first. This occurred several times, and left no doubt in my 

 own mind of the aurora being at one time above, but at another below, the canopy formed 

 about our zenith. The supposition of the light being at no great elevation, is strengthened 

 by the different appearances exhibited by the aurora at the same times, to observers not 

 more than from ten to thirty miles apart ; and also by its being visible to persons on 

 board the ship at Chamisso Island after it had vanished in Escholtz Bay, only ten miles 

 distant, as well as by the aurora being seen by the barge detached from the Blossom 

 several days before it was visible to persons on board the ship, about two hundred miles to 

 the southward of her. Captain Franklin has mentioned a similar circumstance in his 

 notices on the Aurora Borealis in his first expedition, when Dr. Richardson and Mr. 

 Kendall were watching for the appearance of the meteor by agreement, and when it was 

 seen by the former actively sweeping across the heavens and exhibiting prismatic colours, 

 without any appearance of the kind being witnessed by the latter, then only twenty miles 

 distant from his companion. Captain Parry also, in his third voyage, describes the aurora 

 as being seen even between the hills and the ship anchored at Port Bowen." Still, it is 

 unquestionable, that the aurora occasionally occurs in the highest regions of the atmo- 

 sphere, as in the grand example of 1716, which was simultaneously observed in places 

 very remote from each other, and ascertained to be visible from latitude 50 north, all 

 over Europe, between the confines of Russia on the east and Ireland on the west, 

 a sufficient evidence of its very great altitude. 



From optical phenomena belonging to the electric class, or which are supposed to have 

 electrical connections, we proceed to consider the appearances which simply result from 

 peculiar atmospheric conditions. 



M M 



