Observations in Siberia. 5 



Commencing with the intensities of the highest order, the 

 curve drawn through the countries surrounding Hudson's bay 

 is laid down from observations made at occasional intervals, 

 from Regent's inlet in the north-west quarter, by Baffin's in 

 the north, to Davis' strait in the north-east ; and again at New 

 York in the south. In places situated under this curve a needle, 

 freely suspended, which required 300 seconds to perform a 

 given number of vibrations (designated by n) in London, would 

 perform the same number of vibrations (in integer numbers) in 

 269 seconds. In the space included by this curve, within 

 which, except at New York, no observations have hitherto been 

 made, it may be presumed that the intensity progressively in- 

 creases until it attains its maximum at a central point, for the 

 observations made in receding from the curve in different 

 directions, namely at Melville island, in Greenland, and to the 

 southward of New York, all manifest an opposite tendency. 



The observations of M. Hansteen have made known the re- 

 appearance, in Siberia, of an equal intensity to that beneath 

 the curve which has been just described $ forming a curve pro- 

 bably similar in figure, but of smaller dimensions, around a 

 point of maximum intensity situated in longitude 102° east of 

 Greenwich (which is, as nearly as can be judged, 180° from 

 the present position of the corresponding point in Hudson's 

 bay) and in latitude apparently somewhat to the north of 60°, 

 but which will be more particularly determined in the present 

 summer. M. Hansteen has traced the southern band of this 

 curve below the 60th parallel, from the Jenisei river on the 

 west, to the longitude of 1L5° E. (25° east of the Jenisei), and 

 latitude of 61°, where it pursues a direction nearly north and 

 south. It may be remarked of the Siberian curve, that the 

 space which it incloses is considerably less than the corre- 

 sponding curve in America; a circumstance consistent with the 

 supposition already noticed, that the maximum intensity in 

 Siberia is inferior in attractive force to the maximum in Hud- 

 son's bay : consequently, curves of equal intensity are encoun- 

 tered at a less distance from the point of maximum in Siberia 

 than in America. 



The second curve on the American side connects those 

 places where the needle, introduced for illustration, would per- 



