equinoctial Circle of the Earth
_and of a Terrella_.

As conceived by astronomers the aequinoctial circle is equidistant from
both poles, cutting the world in the middle, measures the motions of their
_primum mobile_ or tenth sphere, and is named the zone of the _primum
mobile_. It is called aequinoctial, because when the sun stands in it
(which must happen twice in the year) the days are equal to the nights.
That circle is also spoken of as _aequidialis_, wherefore it is called by
the Greeks [Greek: isemerinos]. In like manner it is also properly called
Aequator, because it divides the whole frame of the earth between the poles
into equal parts. So also an aequator may be rightly assigned to a
terrella, by which its power is naturally divided, and by the plane of
which permeating through its centre, the whole globe is divided into equal
parts both in quantity and strength (as if by a transverse septum) between
verticities on both sides imbued with equal vigour.

* * * * *

CHAP. X.

Magnetick Meridians of the Earth.

Meridians have been thought out by the geographer, by means of which he
might both distinguish the longitude and measure the latitude of each
region. But the magnetick meridians are infinite, running in the same
direction also, through fixed and opposite limits on the aequator, and
through the poles themselves. On them also the magnetick latitude is
measured, and declinations are reckoned from them; and the fixed direction
in them tends to the poles, unless it varies from some defect and the
magnetick is disturbed from the right way. What is commonly called a
magnetick meridian is not really magnetick, nor is it really a meridian,
but it is understood to pass through the termini of the variation on the
horizon. The variation is a depraved deviation from a meridian, nor is it
fixed and constant in various places on any meridian.

* * * * *

{80} CHAP. XI.

Parallels.

In parallel circles the same strength and equal power are perceived
everywhere, when various magneticks are placed on one and the same parallel
either on the earth or on a terrella. For they are distant from the poles
by equal intervals and have equal tendencies of declination, and they are
attracted and held, and they come together with like forces; just as those
regions which are situated under the same parallel, even if they differ in
longitude, yet we say possess