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ON THE MAGNETIC INTENSITY OF THE EARTH. 7? 
in the North Polar map annexed to this report. If the reader 
will nowrefer tothat map (PlateIV.), he willsee that this position 
will by no means accord with that which the observations point 
out for the maximum of intensity. We are not, indeed, enabled 
to assign the position of the latter as nearly as in the case of 
the dip; but it must clearly be in a much lower latitude. The 
intensities observed in Baffin’s Bay and the Polar Sea have 
all a much lower value than at New York; and the general 
configuration of the lines of intensity would rather point to a 
maximum in the vicinity of the shores of Hudson’s Bay. 
‘This remarkable feature of the system was first brought to 
notice in the account of my magnetic observations published 
in 1825*. Ina point of so much interest, it is natural to in- 
quire whether there is any indication of a similar separation at 
the principal pole of the opposite hemisphere. Observations 
as yet do not enable us to assign with sufficient approxima- 
tion the places of the maxima in that quarter; but we are in 
possession of a leading fact, which, by its complete analogy 
with the phenomena at New York, gives strong ground for 
believing that in the southern hemisphere also the places of 
the maxima of the two phznomena are distinct. Ihave already 
noticed the almost identity of the force at Hobart Town and 
NewYork, under nearly equal geographical latitudes; but there 
is yet another feature which completes the analogy, and bears 
directly on the point now treated of. At New York we have 
the highest intensity of the northern hemisphere, 1°80, with a 
dip of 73° 07’; at Hobart Town the highest intensity of the 
southern hemisphere, 1°82, with a’dip of 70° 35’. In both hemi- 
spheres the highest intensity united with a comparatively low 
dip. Nor in that quarter is Hobart Town a solitary instance of 
in a north-west and south-east direction, and that the variation lines converge 
not to the point of 90° but to points in this axis. Small differences of position, 
however, have no effect on the reasoning in the text. 
- * It has been viewed by M. Kupffer as having a direct and important bear- 
_ ing on the very interesting question of the physical nature of the magnetism of 
the earth. In the Ann. der Physik, vol. xv., after describing the course of the 
isogeothermal lines (or lines of equal temperature of the earth at 25 metres be- 
low its surface) between the meridians of 80° west aud 60° east of Paris, he has 
discussed the influence which the facts represented by those lines should 
have on the magnetic dip and force, in the case of the earth’s magnetism being 
superficial and induced. The differences of surface temperature affecting the 
intensity but not the dip would cause the isoclinal and isodynamic lines to se- 
parate where otherwise they might have been accordant; and would especially 
separate the places of the maxima, causing the maximum of intensity to be in 
the lower latitude. M. Kupffer considers the fact of their being thus separated 
_ as giving probability to the aforesaid view of the physical nature of the earth’s 
_ magnetism. 
