RECORD OF AURORAL PHENOMENA. 5 



Cumberland House.— Lat. 53° 56' 40" N. Long. 102° 16' 41" W. October 23, 1819, to June 

 13, 1820. Hood. 



"The most material information we had obtained at this period regarded the height of the anrora 

 from the earth. 



The following is the result of the observations that were made at the Basquiau Hill, and at the 

 same time, by Dr. Richardson, at Cumberland House. The instruments used for the purpose 

 were two small wooden quadrants, revolving on pivots and furnished with plummets. Our 

 chronometers were previously regulated ; though great accuracy was not necessary in this par- 

 ticular, as the arches of the aurora are sometimes stationary for many minutes. 



On the 2d of April, the altitude of a brilliant beam was 10°, at lOh. lm. p. m., at Cumberland 

 House. Fifty-five miles S. S. W., it was not visible. As the trees at the latter station rose 

 about 5° above the horizon, it may be estimated that the beam was not more than seven miles 

 from the earth, and twenty-seven from Cumberland House. 



On the 6th of April, the aurora was, for some hours, in the zenith at that place, forming a cou- 

 fused mass of flashes and beams; and in lat. 53° 22' 48" N., long. 103° 7' 17" W., it appeared 

 in the form of an arch, stationary about 9° high, and bearing N. by E. It was therefore 

 seven miles from the earth. 



On the 7th of April, the aurora was again in the zenith, before 10 p. m., at Cumberland House, 

 and in lat. 53° 36' 40" N., and long. 102° 31' 41" W. The altitude of the highest of two 



concentric arches at 9h. p. m. was 9°; at 9h. 30m. p. m. it was 11° 30' ; at lOh. p. m., 15° 



its centre always bearing N. by E. During this time, it was between six and seven miles from 

 the earth. After lOh. p. m., it covered the sky at Cumberland House, and passed the zeuith at 

 the other place. 



These observations are opposed to the general opinion of meteorologists ; they are nevertheless 

 facts. "We have sometimes seen an attenuated aurora flashing across 100° of the sky in a single 

 second; a quickness of motion 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 extremi- 

 ties 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 simi- 

 larly shaped and infinitely larger. I have called them flashes because their appearance 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 iu 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. Numerous 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 corona; borcales, 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 colors, but the other two were faint 

 and uniform. 



