542 



APPENDIX. 



[No. II. 



inconsistent with the height of sixty or seventy miles, the least which has 

 hitherto been ascribed to it. This kind of Aurora is not brighter than the 

 milky way, and resembles sheet-lightning in its motions. 



For the sake of perspicuity, I shall describe the several parts of the Aurora, 

 which I term beams, flashes, and arches. The beams are little conical pencils 

 of light, ranged in parallel lines, with their pointed extremities towards the 

 earth, generally in the direction of the dipping needle. The flashes seem to 

 be scattered beams approaching nearer to the earth, because they are similarly 

 shaped and infinitely larger. I have called them flashes because their appear- 

 ance is sudden, and seldom continues long. When the Aurora first becomes 

 visible, it is formed like a rainbow, the light of which is faint, and the motion of 

 the beams undistinguishable. It is then in the horizon. As it approaches the 

 zenith, it resolves itself at intervals into beams, which, by a quick undulating 

 motion, project themselves into wreaths, afterwards fading away, and again 

 brightening, without any visible expansion or concentration of matter. Nume- 

 rous flashes attend in different parts of the sky. That this mass, from its short 

 distance above the earth, would appear like an arch to a person situated at the 

 horizon, may be demonstrated by the rules of perspective, supposing its parts 

 to be nearly equidistant from the earth. An undeniable proof of it, however, 

 is afforded by the observations of the 6th and 7th of April, when the Aurora 

 which filled the sky at Cumberland-House, from the northern horizon to the 

 zenith, with wreaths and flashes, assumed the shape of arches at some distance 

 to the southward. 



But the Aurora does not always make its first appearance as an arch. It 

 sometimes rises from a confused mass of light in the east or west, and crosses 

 the sky towards the opposite point, exhibiting wreaths of beams, or coronae 

 , boreales, in its way. An arch, also, which is pale and uniform at the horizon, 

 passes the zenith without displaying any irregularity or additional brilliancy ; 

 and we have seen three arches together, very near the northern horizon, one of 

 which exhibited beams and even colours, but the other two were faint and 

 uniform. 



On the 7th of April, an arch was visible to the southward, exactly similar to 

 that in the north, and it disappeared in fifteen minutes. It had probably passed 

 the zenith before sun- set. The motion of the whole body of Aurora is from the 

 northward to the southward, at angles not more thon 20° from the magnetic 



