zg 
1882.] The Principles of Magnetism. 
accordance therewith. The needle must tend to enter into 
astatic relations with these masses. But these masses are 
numerous, and all tend to assume astatic relations with each 
other. Yet they cannot all assume this relation. The 
mutual action of any two of them is hindered by the adtion 
of the many more distant masses. The result is that local 
relations of position cannot be assumed, but that general 
relations must arise, the magnetic masses in one sedtion of 
the earth becoming astatic with those in another sedtion. 
The diredtion assumed by the needle, for instance, is not 
astatic with that of the superficial magnetic masses of the 
earth, for they undoubtedly agree with it in diredtion. It 
must therefore be in astatic relation with more deep-lying 
masses. But the needle points in the same diredtion at 
every point in the equatorial surface. It follows that the 
astatic tendency between the superficial magnetic masses is 
at every point opposed by a constant energy which can only 
come from the deep-lying figures of the earth. Thus we 
may view our globe in its equatorial plane, and for some 
distance to the north and south, as constituting a cylindrical 
mass, the magnetism of whose superficial regions is opposite 
in diredtion to that of its central regions, while the north 
and south pointing of surface magnets must arise from their 
astatic relations of attradtion with south and north pointing 
magnetic masses in the earth’s interior. The relation, in 
short, is that to which the consideration of the mutual 
adtion of minute magnets led us. Instead of each two 
separate magnetic masses entering into individual local rela- 
tions, the whole sum of magnetic masses enters into general 
relations, and the earth possesses an axial magnetism oppo- 
site in diredtion to its surface magnetism. 
The axial magnetism occupies the whole extent of the 
earth’s axis, and displays itself at the poles, the axis being 
everywhere equally affedted by the surrounding exterior sur- 
face. (This, of course, requires that the earth should be 
throughout equally magnetic, and the irregularity of its 
adtual magnetism must produce a certain degree of inhar- 
mony in the result.) But on the surface that adtion obeys 
another rule. If we take the magnetic needle northward 
from the equator, it at once feels a preponderant influence 
from the greater mass of magnetic matter to the south. It 
no longer continues parallel with the earth’s axis, but 
“ dips,” its astatic relations with the axis being disturbed. 
The axial influence upon it may continue the same, but the 
surface influence is no longer balanced. At the equator the 
equal “ end-to-end ” pull of the superficial masses to the 
