must be sought, why a piece of iron when touched by a loadstone acquires a
disposition to motion toward the opposite pole of the earth, and not toward
that {126} pole of the earth to which that pole of that loadstone turned by
which it was excited. It has been pointed out that iron and loadstone are
of one primary nature; when the iron is joined to the loadstone, they
become, as it were, one body, and not only is the end of the iron changed,
but the remaining parts also are affected along with it. A, the north pole
of a loadstone, is placed against the cusp of a piece of iron; the cusp of
the iron has now become the southern part of the iron, [Illustration]
because it is touching the northern part of the stone; the cross-end of the
iron has become the northern. For if that contiguous magnetick substance be
separated from the pole of the terrella, or from the parts near the pole,
the one end (or the end which, whilst the connection was kept up, was
touching the northern part of the stone) is the southern, whilst the other
is the northern. So also if a versorium excited by a loadstone be divided
into ever so many parts (however small), those parts when separated will,
it is clear, arrange themselves in the same disposition as that in which
they were disposed before, when they were undivided. Wherefore whilst the
cusp remains over the northern pole A, it is not the southern end, but is,
as it were, part of a whole; but when it is taken away from the stone, it
is the southern end, because when rubbed it tended toward the northern
parts of the stone, and the cross (the other end of the versorium) is the
northern end. The loadstone and the iron make one body; B is the south pole
of the whole; C (that is, the cross) is the northern end of the whole;
divide the iron also at E, and E will be the southern end with respect to
the cross; and E will likewise be the northern end in respect to B. A is
the true northern pole of the stone and is attracted by the southern pole
of the earth. The end of the iron which is touched by the true boreal part
of the stone becomes the southern end, and turns to A, the north [pole] of
the stone, if it be near; or if it be some distance from the stone it turns
to the north [pole] of the earth. So always iron which is touched (if it is
free and unrestrained) tends to the opposite part of the earth from that
part to which the loadstone that touched it tends. Nor does it * make any
difference how it is r