AURORA BOREALIS. • 217 



amounts to at least 40. "We thus sec that the region of greatest auroral action 

 is a zone of an oval form, surrounding the nortli pole, and whose central line 

 crosses the meridian of Washington in latitude 56°, and tlio meridian of St. 

 f Petersburgh in latitude 71°. Accordingly, auroras arc more frequent in the 

 United States than they are in the same latitudes of Eurojie. On the parallel 

 of 45^, we find in North America an average of 40 auroras annually, but in 

 Europe less than 10. 



The form of this auroral zone does not bear any resemblance to the lines of 

 equal magnetic intensity, but it does bear some resemblance to the lines of 

 equal magnetic dip. Throughout Asia the line of 80° dip runs nearly through 

 the centre of the auroral zone, but in America it runs sensibly south of it. It 

 bears al-^o considerable resemblance to a magnetic parallel, or line everywhere 

 ])erpendicular to a magnetic meridian ; and the coincidence of this result with 

 the uniform position of auroral arches, naturally suggests the idea of a real con- 

 nexion between the two phenomena. 



Auroras in the southern hemisphere. — "We have but a few observations of the 

 aurora in the southern hemisphere. The most complete record of this kind 

 which I have found is that made at the British Magnetic Observatory, at llo- 

 barton, Van Dieman's Island, during the years lS41-'48. These observations 

 have been published by the British government, and embrace 5 auroras in 1841, 

 12 in 1842, 2 in 1844, 1 in 1846, 9 in 1847, and 5 in 1848, making 34 auroras 

 in 8 years, being an average of 4^- per year ; or if we leave out of the account 

 the years 1843 and 1845, we have an average of 5| per year. Hobarton is in 

 latitude 42° 52' south, and the magnetic dip in IS4o was 70° 35'. This dip is 

 the same as is found in the southern part of England, or in the United States 

 near Baltimore, and the average number of auroras seen annually in each of 

 these regions is from 6 to 7. We hence infer that auroras in the southern 

 hemisphere are nearly if not quite as frequent as they are in corresponding 

 magnetic latitudes of the northern hemisphere. From August 28 to September 

 2, 1859, throughout the southern part of South America and also in Australia, 

 the aurora exhibited a magnificence such as is seldom witnessed in correspond- 

 ing northern latitudes. The observations are too few to enable us to inter 

 what is the geographical distribution of auroras in the southern hemisphere, 

 but they are quite consistent with the supposition that this distribution bears 

 considerable analogy to that in the norihern hemisphere. 



Auroras seen simultaneoushj in both hemispheres. — By comparing the records 

 of auroras in the northern hemisphere with the observations made at Hobarton, 

 already referred to, we find the coincidences of dates are very remarkable. Out 

 of the 34 auroras observed at Hobarton, in 11 of the cases an aurora was seen 

 on the same day at New Haven. TheSfe observations were not strictly cotem- 

 poraneous, for Hobarton and New Haven being in nearly opposite longitudes, 

 when an aurora was seen at Hobarton it could not be seen at New Haven, ou 

 account of the presence of the sun ; but in 1 L cases, an aurora was seeu'withia 

 about twelve hours of its appearance at Hobarton. In several cases when an au- 

 rora was seen at Hobarton it was cloudy at New Haven, and there were eight 

 other corresponding cases in which an aurora was seen at some one of the acad- 

 emies in New York, although not noticed at New Haven. In four additional 

 cases an aurora was seen at Toronto, when none was recorded at New Haven 

 or in the State of New York. Tl'^i'C remain, then, only 11 cases of auroras at 

 Hobarton for which we do not find corresponding observations from one of 

 these three sources in the northern hemisphere, and in eight of these cases the 

 sky was overcast from New Haven to Toronto. In each of these 11 cases an 

 aurora was observed in England, or tliere were observed unixsual disturbances 

 of the magnetic instruments, indicating the existence of an aurora at no very 

 remote station. So far, then, as a conclusion is authorized from so small a uum- 



