352 Prof. Hansteen's New Chart of Magnetic Intensity. 



The uppermost curve on the left hand, where the intensity is 

 1.7 returns into itself in mi oval form, and surrounds the whole 

 of Hudson's Bay, touching nearly the 70th degree of north 

 latitude. The maximum intensity appears to be 1.8, and 

 occurs in the centre of the above oval near the bottom of 

 Hudson"'s Bay, at a distance of' more than ^h"" from the North 

 Pole of the earth. This point is consequently altogether dif- 

 ferent from that point where the dip is = 90°, a result which 

 perfectly agrees with Professor Hansteen's theory of two mag- 

 netic axes. In his Researches respecting the magnetism of the 

 earth, p. 373ihe has already hinted that the inclination of the 

 magnetic axes must be greater thaii is there assumed, a fact 

 which the chart of intensity plainly shows, and by previously 

 assuming this angle at 35° he found that there was such a very 

 near agreement between the calculated and ol^served variations, 

 dips, and intensities, that he has no doubt that the theory will 

 perfectly harmonize with the observations. 



In every meridian there is a minimum of intensity near the 

 equator ; but these minimums are of different values in differ- 

 ent meridians. The greatest of these minimums occurs in 

 about 112° west longitude from Ferro, and about 7° north la- 

 titude, and amounts to 1.51. The least minimum occurs in 

 50^ east longitude, and about 14° south latitude, and amounts 

 to 0.8. A line joining all these points of least intensity would 

 be called the line of the minima. This curve, it must be ob- 

 served, is very different from the line of the dip. It would be 

 of great interest to the theory to determine, by accurate expe- 

 riments, the ratio between the greatest and least minimum, and 

 the situation of the two points where they occur. The eccen- 

 tricity of the magnetical axes might thus be exactly determined. 



As the chart does not contain the northern parts of Europe, 

 we may mention that the curve line of 



1.6 passes north through Greenland. 



1.5 passes south of Iceland, and turns round the north of 

 Lapland. 



1.4 passes through Edinburgh, through Norway, Sweden, 

 Finland, and south of Archangel. 



1,3 passes through Madrid, Austria, Poland, &c. 



