tick power excels light, in that it is not hindered
by any opaque or solid substance, but proceeds freely, and extends its
forces on every side. In a terrella and globe-shaped loadstone the
magnetick power is extended outside the body in an orbe; in a longer one,
however, not in an orbe, but it is extended in an ambit conformably to the
shape of the stone. As in the somewhat long stone A, the vigour is extended
to the ambient limit F C D, equidistant on every side from the stone A.

[Illustration]

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{78} CHAP. VIII.

On the geography of the Earth,
_and of the Terrella_.

Desiring that what follows may be better understood, we must now say
something also about magnetick circles and limits. Astronomers, in order to
understand and observe methodically the motion of the planets and the
revolution of the heavens, and to describe with more accuracy the celestial
attire of the fixed stars, settled upon certain circles and definite limits
in the sky (which geographers also imitate), so that the varied face of the
earth and the beauty of its districts might be delineated. But we, in a way
differing from them, recognize those limits and circles, and have found
very many fixed by nature, not merely conceived by the imagination, both in
the earth and in our terrella. The earth they mark out[166] chiefly by
means of the aequator and the poles; and those limits indeed have been
arranged and marked out by nature. The meridians also indicate straight
paths from pole to pole through distinct points on the aequator; by which
way the magnetick virtue directs its course and moves. But the tropics and
arctic circles, as also the parallels, are not natural limits placed on the
earth; but all parallel circles indicate a certain agreement of the lands
situated in the same latitude, or diametrically opposite. All these the
Mathematicians use for convenience, painting them on globes and maps. In
like manner also in a terrella all these are required; not, however, in
order that its exterior appearance may be geographically delineated, since
the loadstone may be perfect, even, and uniform on all sides. And there are
no upper and lower parts in the earth, nor are there in a terrella; unless
perchance some one considers those parts superior which are in the
periphery, and those inferior which are situated more towards the centre.

* * * * *

{79} CHAP. IX.

On the A