174 Prof. Hansteen on the Number and Situation 
its two poles. Thence we must consider the four magnetic 
points found above, as the ends of two magnetic axes:—which 
of them belong to one another, can only be ascertained by a 
combination of the declinations and dips calculated from theory 
with those found by observation. ‘That hypothesis must be 
correct, in which theory and experience agree. The poles A 
and B are at about the same distance from the terrestrial poles, 
and therefore very nearly diametrically opposed: besides, they 
are much stronger than the poles a and 6; whence it seems 
natural to assume that A and B are the terminating points of 
one magnetic axis,and a and b those of the other, ‘Therefore 
these two magnetic axes cross one another without intersecting 
each other, or passing through the centre of the earth: the 
centres of both lie much nearer the surface in the South Sea, 
than on our side of the earth. R 
This naturally produces several questions, which we cannot 
yet answer satisfactorily: What is tt that produces these two 
magnetic axes in the earth? What is the cause of their motion ? 
How are we to imagine the possibility of this motion within the 
solid mass of the earth? Concerning the first question, we have 
to consider that the magnetic powers are incorporeal essences, 
which, like the light, penetrate the densest bodies without be- 
ing subject to the laws of gravitation. A magnetic axis, there- 
fore, is nothing but a direction in a physical body in which 
these powers act. Ina prismatic piece of steel these powers 
may be separated by simply passing a magnet over it; they 
may be destroyed by rubbing in a contrary direction; or they 
may even be inverted, so that a northern pole be changed into 
a southern, and vice versa, without the internal position or me- 
chanical connexion of the material particles being in the least 
altered. If then the interior mass of the earth consists of a 
material in which magnetic powers may be excited (and the 
above experience compels us to assume this hypothesis), the 
same causes which have excited the magnetic power may, 
under different circumstances, produce a different direction in 
the position of the axes, without there being any necessity of 
having recourse to an internal mechanical motion. Thus then 
the answer to the first question will probably also include that 
to the second. That to the third is of no difficulty. Light 
is the active principle of nature. The effect produced by the 
solar light, and the warmth excited by it, on the surface and 
atmosphere of the earth, is sufficiently known. The develop- 
ment and precipitation of aqueous vapour in the atmosphere, 
and the electricity which is thereby excited, are the effects of 
light and heat most generally known. The essential difference 
between electricity and magnetism, which was assumed ac- 
cording 
