REV. JAMES FARQUH ARSON ON THE AURORA BOREALIS. 113 



of the vertical arch, that some reporters, quoted by Mr. Dalton, state the light 

 towards the extremities to be more intense than that at the zenith. In this 

 fringe-like arrangement a line from the eye, directed considerably towards the 

 East or West, would penetrate and collect the light of many parallel streamers; 

 whereas one directed to near the zenith would, on account of their vertical 

 position, penetrate only a few. 



I now proceed to the question of the height of the aurora borealis above the 

 surface of the earth. In the paper in the Edinburgh Philosophical Journal, 

 1823, 1 had inferred, from the bright phosphorescent light of a cloud apparently 

 under an aurora, that they were in contact, or nearly so, with each other. 

 Another similar appearance, of a still more decided character, in the autumn 

 of 1825, but the precise date of which I have not noted, confirmed, in my 

 mind, the justness of the inference. In a dark evening, without moon, an ex- 

 tended mass of clouds stretching along the N. and N.E. quarter, not much 

 raised above the visible horizon, and having a clear sky above it, in which there 

 was pla3dng a fine aurora of vertical streamers, with their lower extremities 

 apparently touching it, was observed giving out at its upper side a fitful but 

 bright white light, more vivid and conspicuous amidst the darkness than if it 

 had been illuminated by the rising moon. Similar clouds in other parts of the 

 horizon exhibited no such light. It was impossible for a spectator to refer the 

 aurora to a distance more remote than that of the mass of clouds ; or to be- 

 lieve that the former and the light of the latter were not parts of the same 

 phaenomenon. Mr. Otley (Phil. Trans. /. c.) appears to have witnessed a similar 

 phaenomenon. " About 7 P. M. a dense cloud appeared in the horizon to 

 the N.N.W., bounded by a bright line, the rest of the heavens being starry. 

 Presently beams of an aurora began to shoot towards the Great Bear." Tiie 

 appearances now mentioned are of a nature to admit, probably, of frequent 

 verification. 



But a combination of circumstances attended the aurora borealis, as seen by 

 me on the 22nd of November 1825, and described above, which seem decisive 

 of this question. On that evening, besides the small detached clouds of the 

 eastern and zenith part of the heavens coming slowly from the north, another 

 of a quite different character extended along the whole western pai-t of the sky 

 to about 25° or 30° above the horizon. It was one dense sheet or stratum, 



MDCCCXXIX. Q 



