No. II] AURORA BOREALIS. 



543 



meridian. The centres of the arches were as often in the magnetic as in the 

 true meridian. 



The colours do not seem to depend on the presence of any luminary, but to 

 be generated by the motion of the beams, and then only when that motion is 

 rapid, and the light brilliant. The lower extremities quiver with a fiery red 

 colour, and the upper with orange. We once saw violet in the former. The 

 number of Aurora visible in September was two ; in October three ; in No- 

 vember three ; in December five ; in January five ; in February seven ; in 

 March sixteen ; in April fifteen ; and in May eleven. Calm and clear weather 

 was the most favourable for observation ; but it is discernible in cloudy weather, 

 and through mists. We could not perceive that it affected the weather. The 

 magnetic needle, in the open air, was disturbed by the Aurora, whenever it ap- 

 proached the zenith. Its motion was not vibratory, as observed by Mr. Dalton ; 

 and this was, perhaps, owing to the weight of the card attached to it. It moved 

 slowly to the E. or W. of the magnetic meridian, and seldom recovered its 

 original direction in less than eight or nine hours. The greatest extent of its 

 aberration was 45'. 



A delicate electrometer, suspended at the height of fifty feet from the ground v 

 was never perceptibly affected by the Aurora, nor could we distinguish its 

 rustling noise, of which, however, such strong testimony has been given to us, 

 that no doubt can remain of the fact. The conclusions to be drawn from the 

 above will be found in the observations for the winter of 1820. 



An Account of the Aurora Borealis, seen at Cumberland-House, between the 23d 

 of October, 1819, and the ISth of June, 1820; Lat. 53° 56' 40" N. Long. 

 102° 16' 41" W. Variation 17° IT 31" E. 



From the 23d of October to the 25th of November, the aurora was not visi- 

 ble, or it did not appear before one a. m. 



November 26th, at one a. m., an Aurora, arched like a rainbow, about 20° 

 high; centre bearing north ; colour pale-yellow, faint. At eight p.m., a very 

 faint arch, centre north. 



December 6th, at ten p. m., a faint-arched Aurora, centre N.b. E. 



8th. A similar Aurora, centre north, at ten p r m. 



