Mr Potter on the Aurora Borealls. 29 



extent of the upper edge without the appearance of a single 

 streamer. The altitude during its brightest and best defined 

 period was 10° to 12°. It then became gradually fainter, and 

 its altitude kept decreasing. At 6 to 8 minutes past 12, its 

 altitude did not exceed 10°. It then became very diffuse in 

 the magnetic north, and at 15 minutes past 12 it was dying 

 away very quickly, its altitude only 5°, and still no appearance 

 of streamers from it. Now, as they are said never to proceed 

 from the south towards the north, but the reverse, and as this 

 arch was in the northern part of the heavens, its decrease in ap- 

 parent altitude could only arise from a real decrease in its height 

 from the surface of the earth. 



One of the most brilliant displays of the aurora we have 

 had visible here was the one on the evening of Christmas day, 

 (for unfortunately the sky was obscured by clouds during 

 that of the 7th January, which was so fine a one to the inha- 

 bitants of the south of England ;) and though the moon was 

 shining brightly, and only about four days from the full, it 

 was by far the most brilliant and extensive that I have seen. 

 I was told about 40' past 6 that an arch of an aurora was vi- 

 sible; at about 10' to 7 it was regular and well-defined, pas- 

 sing a little below the pole star ; about 15 / afterwards its under 

 edge was higher than a Folaris, and at the western extremity 

 it passed about 6° to the south of a Aquilae, counted on the ho- 

 rizon ; its eastern extremity was diffuse and not so well-de- 

 fined ; about 7 o'clock another arch had formed at about 15° 

 of elevation, y Ursae Majoris being in its under edge ; about 

 10' after, the next star in the tail of the Bear was in its under 

 edge, or its altitude was about 20°, at which position it re- 

 mained during the display ; its under edge passed about 5° to 

 the north of a Jquilce counted on the horizon. The higher 

 arch disappeared and reappeared several times ; when, at its 

 most southern position, it passed very near the zenith, Capella 

 being in its southern edge, and the more remarkable stars in 

 Cassiopeia being covered by it ; it appeared about 6° to 7° 

 broad, and no part of the aurora passed farther to the south 

 than this arch, excepting, perhaps, a few streamers, which shot 

 past its western edge towards the point to which the south pole 

 of the dipping needle tends, so that it will form a good object 



