ubstances would have a dip by their own nature
below the horizon; and at the poles the directions would be perpendicular,
which appears in our discussion _On Declination_.

[Illustration]

_A round stone (or terrella) cut in two at the aequator;_ and all the cusps
have been touched by the pole A. The points at the centre of the earth, and
between the two parts of the terrella which has been cut in two through the
plane of the aequator, {136} are directed as in the present[209] diagram.
This would also happen in the same way if the division of the stone were
through the plane of a tropick, and the mutual separation of the divided
parts and the interval between them were the same as before, when the
loadstone was divided through the plane of the aequator, and the parts
separated. For the cusps are repelled by C, are attracted by D; and the
versoria are parallel, the poles or the verticity in both ends mutually
requiring it.

[Illustration]

_Half a terrella by itself and its directions, unlike the directions * of
the two parts close to one another as shown in the figure above_. All the
cusps have been touched by A; all the crosses below except the middle one
tend toward the loadstone, not straight, but obliquely; because the pole is
in the middle of the plane which before was the plane of the aequator. All
cusps touched by places distant from the pole move toward the pole (exactly
the same as if they had been rubbed upon the pole itself), not toward the
place where they were rubbed, wherever that may have been in the undivided
stone in some latitude between the pole and the aequator. And for this
reason there are only two distinctions of regions, northern and southern,
in the terrella, just {137} as in the general terrestrial globe, and there
is no eastern nor western place; nor are there any eastern or western
regions, rightly speaking; but they are names used in respect of one
another toward the eastern or western part of the sky. Wherefore it does
not appear that Ptolemy did rightly in his _Quadripartitum_, making eastern
and western districts and provinces, with which he improperly connects the
planets, whom the common crowd of philosophizers and the superstitious
soothsayers follow.

* * * * *

CHAP. X.

On Mutation of Verticity and of Magnetick
Properties, or on alteration in the power
_excited by a loadstone_.

Friction with a loadstone gives to a piece of iron a verticity