1835.] Magnetic Intensity of the Earth 63 



and Kamschatka, through the Southern Sea to the Philip- 

 pines. Dr. Erman of Berlin, who travelled through 

 Russian Asia, embarked at Kamschatka and returned by 

 Cape Horn, communicated also much interesting matter. 

 The Emperor of Russia sent a number of observers to the 

 Caucasus, in 1829, under professor KupfFer. who were 

 supplied with the proper instruments for ascertaining the 

 magnetic force. Captain Freycinet supplied materials 

 likewise. 



Hansteen has fixed upon the smallest intensity observed 

 by Humboldt as unity, although recent researches have led 

 to the belief, that this is not the absolute minimum, but 

 that we must look for this point in Southern Africa. 



The point of greatest intensity is New York, where it 

 amounts to 1*801. Yet this is probably not the maximum 

 as the direction of the line appears to indicate, that the 

 intensity on the West coast of Hudson's Bay may be as 

 high as 1*9. If we follow the 60" of parallel from Hudson's 

 Bay to Christiania, it will be observed, that this Latitude 

 cuts the different curves which indicate the intensities 1-8 

 1-7— 1-5— 1-4. 



The isodynamic line of 1*4 which passes from Jamaica 

 and the Azores through England to Christiania, turns then 

 easterly and cuts the 60 degree of latitude at St. Peters- 

 burg. In this parallel a minimum of intensity is observed 

 between Christiania and St. Petersburg in the meridian of 

 Abo. Following out this parallel to the east, the intensity 

 is found to increase, being at Bogoslowsk 1-5, and at 120° 

 east from Ferro 1*7. Between 120° and 130° it attains its 

 maximum of 1*72, and further east it decreases, so that 

 about 123° it is 1*7, and in the meridian of 168° 1*6. 



About 167° it reaches another minimum = 1*56 at Olu- 

 torskoi. The greatest intensity observed in Siberia was 

 detected by Lieut. Due at Wilwisk = 1*76. Hansteen in- 

 fers from these data, that in the northern hemisphere, 

 two magnetic mean points or poles exist, and that the 

 Western Pole, in North America, exhibits a stronger in- 

 tensity than the eastern one in Siberia. 



The observations with respect to the magnetic force in 

 the southern hemisphere are extremely scanty ; those of 

 King and Liitke only extending along the coast of South 



