1 882c] The Principles of Magnetism. 31 
nuous, and the general action of the earth’s magnetism 
must be weakened by such local reversing action. 
If now, instead of taking our testing magnet over the 
earth’s surface, we take it inward towards the axis, other 
phenomena than those above considered must arise. If this 
be done in the plane of the equator, the necessary reversal 
of magnetism as the axis is approached cannot take place 
by means of dip, for the equality of northern and southern 
influences produces an equal tendency to dip in the two 
opposite directions. It can only take place, then, through 
a weakening and gradual disappearance of the magnetic 
energy, and its reappearance in the opposite direction as the 
axis is neared, until finally a full opposite energy is gained 
at the axis. Thus between the astatic regions of axis and 
surface there must be an intermediate region of weaker, 
and a zone of no magnetism, produced by these opposing 
influences. 
But north and south from the equator the conditions are 
necessarily different. If the testing magnet be carried in- 
wards at a point between the equator and the north pole, 
“ dip ” phenomena must appear. If it be carried southward 
from the north pole over the surface a dip reverse to that 
displayed when it is carried from equator to pole will occur. 
And if, instead of continuing this movement to the equator, 
the magnet be carried beneath the surface at any point suffi- 
ciently southward, its reverse dip must continue and grow 
more declared, from the increased vigour of the superficial 
influence. At a certain depth beneath the surface, then, it 
would assume the direction which it possesses at the equator, 
that of reverse parallelism with the axis. Going still deeper 
the reversing influence must continue, and become complete 
at the axis. Thus the effeCt upon the magnet, of thus 
taking it inward to the axis, would probably be the same as 
if it had been taken on over the surface to the south pole, a 
complete rotation of the direction of its axis taking place in 
either case. Of course it cannot be positively declared what 
would occur in the case of such a movement beneath the 
surface, but the aCtion of the astatic influence must certainly 
tend to produce such a continued rotation. 
(To be continued.) 
