Observations in Siberia. 3 



M. Hansteen has now made, appeared sufficiently conformable 

 to the existing observations to receive their countenance and 

 support. It had so happened that the previous observations, 

 although extending widely over the magnetic parallels in the 

 northern hemisphere, namely, from the least almost to the 

 greatest intensity, were confined in respect to longitude to a 

 space little more than the quarter of a hemisphere ; and to 

 that quarter which is immediately opposite to the countries 

 visited by M. Hansteen. Within the space that had been thus 

 examined, the isodynamic curves appeared to arrange them- 

 selves, with comparatively insignificant deviations, in parallel 

 circles, around a point situated in the north-eastern part of 

 Hudson's bay, and, as nearly as could be judged, about the in- 

 tersection of the 60th degree of geographical latitude with the 

 meridian of 80° west of Greenwich. That a system appa- 

 rently so simple, so like the arrangement of induced magnet- 

 ism in a sphere of iron, and corroborated by the approximation 

 of results observed over a fourth part of a hemisphere, should 

 have been viewed as likely to prove eventually the general 

 system of the globe, is not surprising. It is the peculiar dis- 

 tinction of M. Hansteen to have been led by a more careful 

 consideration of the slight apparent deviations which have been 

 noticed, and of the general disposition on the globe of the lines 

 of Dip and Variation, to infer the existence of a second point 

 of principal magnetic action in the northern hemisphere ; a 

 fact, which by his recent observations must now be regarded as 

 fully established ; the isodynamic curves being found to arrange 

 themselves systematically around two points, one in Hudson's 

 bay and one in Siberia ; and to be governed in the courses 

 which they follow, partly by their distances respectively from 

 those points, and partly by a disparity in the absolute attrac- 

 tive force at the points themselves, the maximum intensity in 

 Siberia appearing to be weaker than the maximum in Hud- 

 son's bay. 



The accompanying sketch of the northern hemisphere may 

 enable me to convey a more distinct notion of the arrangement 

 of the isodynamic curves than could be done by description 

 alone : the portions traced in unbroken lines mark the con- 

 nexion between places at which an equal intensity has been 



B2 



