1835.] * Magnetic Intensity of the Earth. 65 



In the course of his investigations upon the earth's mag- 

 netism, Hansteen has made the interesting remark that the 

 Polar lights derive their origin from the four magnetic 

 points on the earth's surface, where the maximum of inten- 

 sity is observed, and that the irregular movements of the 

 needle during the appearance of the Northern lights, indi- 

 cate the most intimate connexion between them and mag- 

 netism. These movements of the magnet appear in the 

 same instant at distant places, for Hansteen observed on 

 the 26th August 1825, at Tornea, a sudden diminution of 

 the magnetic intensity, while M. Arago at Paris at the 

 same moment remarked a great movement in the needle, 

 and Holmbce at Christiania, and Herzberg at Hardanger 

 noticed an aurora.* 



Lately it was determined at the request of Humboldt,- 

 that magnetic observations should be registered every hour 

 at Berlin, Freiberg, Petersburgh, Kasan,and at Irkutsk an 

 observatory is now in progress. 



It is a point of some importance to attend to the relation 

 between the mean temperature of a place, and its position 

 in respect to the magnetic pole. 



Mercury it is known freezes at Hudson's Bay in 55° N. L., 

 which does not occur in Europe. In his journey in Siberia, 

 Hansteen had the mercury in his thermometer frozen many 

 days between Krasnojarsk and Nishne Udinsk. On the 

 30th of January in 55°| N.L. at Bagranowskaia, he froze 

 three or four pounds of mercury. At Jakutsk in June 1829, 

 Due and Erdman caused a well to be dug, and found the 

 earth frozen at 30 feet, and where a thermometer fell below 

 the freezing point, while in the air it was high. At Turnshansk 

 (65°) Hansteen found the earth frozen considerably under 

 the surface, while the temperature of the air was 25° R. 

 (56°i F.) in the month of June. At Terra del Fuego the 

 climate is very severe, although this island stretches from 

 23° to 55°, and is surrounded by the great ocean which tends 

 to meliorate the climate. Hence it appears that the tem- 

 perature in the vicinity of three of the magnetic poles, is 



* The discovery of the intimate connexion which subsists between the aurora 

 and magnetism, was demonstrated by Dr. Dalton as early as towards the end of 

 the last century, so that the remark of Hansteen must be considered only as a con- 

 firmation of the fact ascertained by the English philosopher. — Edit. 

 VOL. I. F 



