tate more strongly; but an
orbicular stone * makes it rotate strongly and truly, in accordance with
magnetick rules and its globular form. A long stone, on the other hand,
extended from pole to pole, moves a versorium toward it irregularly; for in
this case the pole of the versorium always looks down on the pole itself.
Similarly also, if the loadstone have been made in the shape of a circle,
and its poles are on the circumference, whilst the body of it is plane, not
globular, if the plane be brought near a versorium, the versorium does not
move with the regular magnetick rotation, as on a terrella; but it turns
looking always toward the pole of the loadstone, which has its seat on the
circumference of the plane. Moreover, if the stone caused the versorium to
rotate by attracting it, then in the first degrees of latitude, it would
attract the end of a short versorium toward the body itself of the
terrella; yet it does not so attract it that they are brought into contact
and unite; but the versorium rotates just so far as nature demands, as is
clear from this example. {196} [Illustration] * For the cusp of a versorium
placed in a low latitude does not touch the stone or unite with it, but
only inclines toward it. Moreover, when a magnetick body rotates in
dipping, the pole of the versorium is not stayed or detained by the pole of
the earth or terrella; but it rotates regularly, and does not stop at any
point or bound, nor point straight to the pole toward which the centre of
the versorium is advancing, unless on the pole itself, and once only
between the pole and the aequator; but it dips as it advances, according as
the change of position of its centre gives a reason for its inclination in
accordance with rules magnetical. The declination of a magnetick needle in
water also, as demonstrated in the following pages, is a fixed
quantity[235]; the magnetick needle does not descend to the bottom of the
vessel, but remains steady in the middle, rotated on its centre according
to its due amount of declination. This would not happen, if the earth or
its poles by their attraction drew down the end of the magnetick needle, so
that it dipped in this way.

* * * * *

CHAP. VI.

On the proportion of declination to latitude[236], and
_the cause of it_.

Concerning the making of an instrument for finding declination, the causes
and manner of declination, and the different degrees of rotation in
dif