6 On M. Hansteen's recent Magnetic 



form n vibrations in 278 seconds. The points which have deter- 

 mined it are, Melville island, in the north-west ; several stations 

 on the west side of Greenland from lat. 76° to lat. 60° in the 

 north-east ; and finally, a greater intensity observed at New 

 York and a lesser at the Havanna ; whence it is concluded that 

 this curve intersects the seabord of the United States at an in- 

 termediate point between those cities. A corresponding inten- 

 sity has been traced by Dr. Erman of Berlin (who accompa- 

 nied M. Hansteen to Siberia) from the mouth of the river Oby, 

 in lat. 68° and long. 70° E., preserving nearly the direction of 

 a meridian to lat. 60°, where it bends gradually to the east- 

 ward, passes between Tobolsk and Narym, and has been ob- 

 served at Kainsk, by M. Hansteen, on its way to its probable 

 southern limit on the Atlantic side, a few degrees south of lake 

 Baikal. 



The third curve is that in which the needle would perform n 

 vibrations in 287 seconds. It is laid down from observations, 

 1st, at the Havanna ; 2d, at the Pendulum islands on the 

 eastern side of Greenland, in latitude 74°.5, where a somewhat 

 greater intensity was found ; and 3d, between Hammerfest 

 near the north cape of Europe, and Spitzbergen. By M. Han- 

 steen's observations it enters the continent of Europe between 

 Archangel and Nova Zembla, and was crossed by him on the 

 route from Moscow to Tobolsk, in 56° and 57° east longitude, 

 and 57° and 58° latitude. 



The fourth curve is that in which the needle would make n 

 vibrations in 297 seconds. Its tracing from observation com- 

 mences, on the American side, near the island of Jamaica, 

 where the time of vibration was 294 seconds. Crossing the 

 Atlantic, it passes through the northern parts of the British 

 islands, and enters Norway south of Bergen. It there became 

 subject to M. Hansteen's observation, who has ascertained its 

 northern limit (from whence it begins to bend to the southward) 

 to be on the shores of the gulf of Bothnia, midway between 

 Stockholm and Tornea. He has since traced its prolongation 

 through St. Petersburg and Moscow. 



It is M. Hansteen's intention to commence the present sum- 

 mer by descending the Jenisei to Touroukansk under the polar 

 circle, in order to extend the tracing of the curve of greatest 



