552 SCIENTIFIC RECORD FOR 1833. 



nearly circulating, movement j the individual perpendicular bars that 

 form it have simultaneously a forward and backward movement ; the 

 whole band changes its place continuously in the sky, and ordinarily one 

 sees many such bands expanded over the sky. The auroral arches seen 

 by observers stationed at northern latitudes have a more regular inva- 

 riable form than these bands, and both these forms are seen by observ- 

 ers in the southern part of the zone of maximum frequency. Accord- 

 ing to Edlund the aurora depends on atmospheric electricity, but a mu- 

 tual dependence on terrestrial magnetism and sun spots is also acknowl. 

 edged, and the parallelism of these with the annual daily variations of 

 atmospheric temperature and pressure force us to trace all back to the 

 same source, the sun. 



Arsuk Fiord is in 61° 15' north latitude. This fiord is 2 miles wide 

 by 25 long, and its shores are steep, rocky cliffs from one to four thou- 

 sand feet high. Midway of its length, on the south side, lies Ivigtut. 

 At this station the aurora light begins with a development in the west 

 over the north of the fiord, and as it progresses eastward follows the 

 direction of the fiord, sometimes covering its entire length, and having 

 outliers over the smaller arms of the fiord; but ordinarily the western 

 part of this auroral band disappears before the development has ex- 

 tended to the eastern end and new bands of light come again from the 

 western end eastward. The phenomenon is best developed at two 

 hours after sunset, and appears then to be near the earth's surface, 

 occasionally only 1,000 feet above sea-level. As a rule, the aurora is 

 fully developed only in calm, clear weather. It most frequently appears 

 during the east wind (the well-known Fohn wind), but is then very un- 

 quiet and dismembered. The author then gives his theory that the au- 

 rora is due to local currents of warm and cold air. (Z. 0. 0. If., xvn, 

 p. 320.) 



Nordenskiold,in his report on the auroras observed in the Bering Sea 

 during the voyage of the Vega in 1878 and 1879, states that in tliose 

 regions the aurora presented an entirely different appearance from what 

 is ordinarily seen in Europe. It consisted regularly of an arch of light 

 five or twelve degrees above the horizon, perfectly quiet, without mo- 

 tion or rays. The inside of this arch was sharply defined, and the so- 

 called dark segment wholly free from light, and generally free from 

 clouds or fog. The upper limit of the arch was not sharply defined, and 

 above it the sky was somewhat illuminated ; occasionally rays issued 

 from this side, especially when several such arches were arianged above 

 each other, which latter appearance was not rare. The brilliant dra- 

 pery and beams reaching the zenith, so common in Europe, were very 

 seldom seen. 



Nordenskiold proposes the following explanation, namely, that the 

 ordinary auroral arches are due to a luminous ring that remains per- 

 manently around the magnetic pole as a central axis, its center being 

 about 2,000 kilometers above the earth's surface, its radius 0.32 of the 



