her over the terrella, like A and B of the divided stone above.
But now if the cusp A, * which has been touched by a loadstone, be the
southern end, and you were to touch and rub with this the cusp of another
iron needle B, which has not been touched, B will be northern, and will
point to the south. But if you were to touch with the northern point B any
other iron needle, still new, on its cusp, this again will be southern, and
will turn to the north. The iron not only receives the necessary strength
from the loadstone, if it be a good loadstone, but also imparts its
acquired strength to another piece of iron, and the second to a third
(always in strict accordance with magnetick laws). In all these
demonstrations of ours it should always be borne in mind that the poles of
a stone, as well as those of iron, whether touched or untouched, are always
in fact and by nature opposite to the pole toward which they point and are
so designated by us, as we have laid down above. For in them all it is
always the northern * which tends to the south, either of the earth or of
the stone, and the southern which tends to the north of the stone. Northern
parts are attracted by the southern of the earth; so in the boat they {129}
tend toward the south. A piece of iron touched by the northern parts of a
loadstone becomes south at the one end and tends always (if it is near and
within the orbe of the loadstone) to the north of the stone, and if it be
free and left to itself at some distance from the stone, it tends to the
northern part of the earth. The northern pole A of a loadstone turns to G,
the south of the earth; a versorium touched at its cusp by the part A
follows A, because it has become southern. But the versorium C, placed
farther away from the loadstone, turns its cusp to F, the north of the
earth, because * the cusp has become southern by contact with the boreal
part of the stone. So the ends touched by the northern part of the stone
are made southern, or are excited with a southern polarity, and tend toward
the north of the earth; those touched by the southern pole are made
northern, or are excited with a northern force, and turn to the south of
the earth.

[Illustration]

* * * * *

CHAP. V.

On the Touching of pieces of Iron
_of divers shapes._

Bars of iron, when touched by a loadstone, have one end north, the other
south, and in the middle is the limit of verticity, like the aequinocti