ON THE PHENOMENA OF TERRESTRIAL MAGNETISM. G7 
Hence M. Hansteen concludes that a more extensive acquain¬ 
tance with the lines of equal magnetic intensity would show them 
to be equally irreconcileable with the hypothesis of a single mag¬ 
netic axis as those of dip and variation are found to be*. 
Having thus prepared and arranged the materials furnished 
by observation, M. Hansteen proceeds, in the 3rd chapter, to 
consider the evidence they afford of the number, situation, and 
movement of the magnetic poles. 
The variation map of 1787 (PI-1.) exhibits a tolerably complete 
systemof the lines of variation. In the neighbourhood of Hudson’s 
Bay, the indication of a point of directing influence is obvious 
in that quarter, evidenced by the characteristic circumstances 
of a rapid convergency of the lines, and of the proximity of great 
easterly and great westerly variations. A similar indication is 
seen to the south of New Holland. In two other quarters also, 
viz. to the south of Cape Horn and in Siberia, are less obvious, 
but still decisive, characteristics of the existence of points of 
directing influence. 
In the map of the dip in 1780 (PI. II.), the arrangement of the 
lines of dip corresponds to the indications thus traced in the lines 
of variation. In each hemisphere the lines of dip have a double 
flexure, those in the northern hemisphere making two loops to 
the southward, and those in the southern hemisphere making 
two loops to the northward. In the lines of dip also the di¬ 
recting influences in Siberia and south-west of Cape Horn are 
observed to be less distinctly marked than those in Hudson’s 
Bay and New Holland. 
In regard to the magnetic force, it has already been seen that 
* In 1825 I published a series of observations which I had made in 1822 and 
1823 on the magnetic dip and intensity at several stations comprised between the 
meridians of 76° W. and 23° E., and the parallels of 12° S. and 80° N. I was 
at that time unacquainted withM. Hansteen’s work, having been little in Europe 
since its publication ; but the irreconcileability of my observations with the hypo¬ 
thesis of a single magnetic axis was too striking to be overlooked, and was ac¬ 
cordingly noticed by me : the direction of the curves of equal dip and of equal 
force was so far from corresponding, that the latter assuredly could not be com¬ 
puted, as had been supposed, by any function of the observed dip. The lines of 
equal dip crossed the geographical parallels of latitude at a small angle which 
nowhere exceeded a few degrees; whilst the isodynamic lines, within the space 
comprised by the observations, might be represented with tolerable approxima¬ 
tion by concentric curves around an assumed maximum of intensity situated 
near Hudson’s Bay. On becoming acquainted with M. Hansteen’s work, I was 
much struck by the accordance of my observations, both of dip and force, with 
the system which he had anticipated from a study of the phenomena elsewhere ; 
and I should not have failed to have noticed this circumstance publicly, had 
not M. Hansteen himself anticipated me in a review of my observations in the 
Annalen der Physih. 
F 2 
