342 Mr Blackader's Account of an Aurora Borealis. 



lypus shoots out from that point, so that, at this season, we ob- 

 serve young polypi, in every situation, on the branches, the 

 whole of the old cells are thus never found entirely deserted, the 

 same cells may repeatedly produce ova and polypi, and the whole 

 zoophyte retain its energy for several seasons. 



Account of an Aurora Borealis, observed at Edinburgh 16th 

 January 182T ; with some particulars of another, of a pre- 

 ceding year. With a Plate. By D. Blackader, Esq. 

 Communicated by the Author. 



jCjLBOUT 9 oVlock, p. M., evening fine, brilhant moonshine, 

 a beautiful white, opaque, drapery of cloud, extending from the 

 zenith to within about 15" of the NW. horizon. The wind had 

 for some days been boisterous and variable, and had veered, in 

 the morning, from NW. to NE. ; but the air was uow calm and 

 serene. In the course of a few minutes the cloudy tissue had 

 entirely disappeared, and a brilliant aurora was exhibited, in 

 rapid change of feature, and distinguished by unusual proximity. 

 Horizontal cloudy vapours, of great tenuity, repeatedly accom- 

 panied its more brilliant evolutions, seeming to support its 

 columns ; appearing and vanishing with the more vivid corus- 

 cations. Thereafter, the aurora became extended, to right and 

 left, fortning the segment of a large circle, although not exceed- 

 ing in altitude more than 1 5°, and, at either extremity, vanish- 

 ing, like the higher strata of clouds, in the blue expanse. This 

 arch may be conceived of by means of the sketch, Plate IV. No. 1 . ; 

 whereof the landscape includes an angle of about 90°, having 

 its centre in the magnetic meridian ; near to which a principal 

 star is seen, at that hour. The lower edge of this arch was al- 

 ways above that star. Subsequently, a second arch was formed 

 in front thereof. 



On the right exti'emity, the arch always presented a broken 

 or interrupted line, with recurrence of separate masses of lumi- 

 nous spears, of a brilliant bluish-white lustre ; a golden tint, and 

 burnished lustre, distinguished the continuous arch of the cen- 

 tral portion, which, towards the left, became coppery. The 

 second, or front line, was uncommonly distinct, and much 

 nearer than the one first formed. Other figures, 'afterwards 



