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ON THE MAGNETIC INTENSITY OF THE EARTH. 71 
are in the longitude of 35° and 140°; in the curve of intensity, 
in those of 20° and 175°. The Siberian portion of the inten- 
sity curve bears consequently a larger proportion to the whole 
area of that curve, than the Siberian portion of the dip-curve 
does to its total area. From the general resemblance of the 
several lines of dip to each other, and of the several lines of 
intensity to each other,—the characteristics of each being - 
always marked, though gradually softening as they approach 
the middle regions of the globe,—the features of distinction 
which are thus strongly marked in the curves compared by M. 
Erman, must exist also in a greater or less degree in many. 
Here, then, is another striking and systematic difference in the 
two species of magnetic lines*. 
2. The lines of intensity in the northern hemisphere system- 
atically indicate the existence of two centres of attraction of 
unequal force. 
The examination of the graphical representation of these 
lines in the maps will convey a clearer apprehension of this 
systematic indication than a lengthened verbal description. 
The higher the values of the intensity of each isodynamic line, 
—in other words, the nearer the lines approach the centres of 
attraction,—the more unequivocal is their testimony. The 
smaller areas included by the curves in the Siberian quarter 
mark the less extensive influence and inferior power of the 
Siberian centre. Looking next at the values of the intensities 
represented by the lines, we find in the neighbourhood of New 
York, a portion of a line of 1:8, to which there is no equiva- 
lent in Asia. The highest intensity there is 1°76, observed by 
Lieut Due at Viluisk, which M. Hansteen believes, and with 
great probability, derived from the configuration of the lines, to 
be the highest existing in that quarter. It is improbable, 
moreover, that the greatest intensity in the American quarter 
should be found so far south as New York; the configuration 
of the lines, as shown particularly in the north polar map, in- 
dicates the maximum to be nearer Hudson’s Bay}. 
* M. Erman remarks that the difference is of that character which would 
appear to indicate for the Asiatic centre a less depth beneath the surface than 
the American. 
+ Since the above was written, the first number has reached London of the 
Observations Météorologiques et Magnétiques faites dans l’étendue de l' Empire 
de Russie, which have been confided to the editorship of M. Kupffer. In the 
introduction we have a formal recognition of the existence of the Siberian pole. 
“La Russie est aussi la terre classique du magnétisme terrestre. Il y aun 
pole magnétique dans le nord de la Siberie.” 
