30 The Principles of Magnetism. January, 
north and south aided the reversing influence of the axial 
magnetism. But at a distance from the equator these sur- 
face influences are no longer equal. If it move north the 
sum of the whole surface influences to the south over- 
balances those to the north, the axial influence is partly 
overcome, and the magnet dips its north pole towards the 
earth’s axis. Going still farther north this influence in- 
creases, and the reversing movement strengthens. At a 
certain distance north the reversion is half completed, and 
the magnet stands perpendicular to the earth’s axis. Con- 
tinuing the northward movement the magnet continues to 
turn, until, when the extremity of the earth’s magnetic axis 
is reached, a complete reversion is produced, and the axis of 
the magnet stands opposite to its position at the equator. 
It has now become a portion of the earth’s axis, and all the 
surface influence is combined to hold it in this position. 
The dipping movements of the magnet here considered 
undoubtedly indicate similar conditions in the earth’s mag- 
netism as a whole. At the equator the earth’s superficial 
magnetism is opposite in direction to its axial. Going north 
from the equator a reversing influence shows itself, the direc- 
tion of the magnetism slowly revolves, at a certain distance 
north it becomes vertical to the axis, still farther north the 
angle becomes greater, and at the magnetic north the rever- 
sion is completed, and the axial magnetic direction assumed. 
Going south the same series of changes occurs, though in 
the opposite direction. The magnetic needle, therefore, may 
be looked upon as a testing magnet, through whose move- 
ments we may become aware of the true magnetic conditions 
of the earth. The complete revolution on its equatorial 
plane, which it makes on passing from the north to the 
south pole, is significant of a like complete revolution in the 
earth’s superficial magnetism, while its assumption of the 
same direction at the two poles is indicative of a fixed 
direction of magnetism throughout the whole extent of the 
axis. 
Were the earth’s magnetism very powerful all local adtion 
would be lost in the general energy, and we could obtain no 
knowledge of magnetic phenomena. As it is, however, the 
mutual influences of two powerful magnets are stronger than 
that of the earth upon either, and they produce an astatic 
effedl upon each other. But on being separated to a certain 
distance the terrestrial vigour overpowers the local, and they 
place themselves — if free to move — in conformity with this 
general vigour. Doubtless similar astatic influences must 
arise interiorly when any two magnetic masses are conti* 
