atorium
(by its versatory nature) indicates the degree of declination.

In a declination instrument the magnetick needle, which
_in a meridional position dips, if turned
along a parallel hangs perpendicularly._

In a proper position a magnetick needle, while by its rotatory nature
conformed to the earth, dips to some certain degree below the horizon on an
oblique sphere. But when the plane of the instrument is moved out of the
plane of the meridian, the magnetick needle (which tends toward the pole)
no longer remains at the degree of its own declination, but inclines more
toward the centre; for the force of direction is stronger than that of
declination, and all power of declination is taken away, if the plane of
the instrument is on a parallel. For then the magnetick needle, because it
cannot maintain its due position on account of the axis being placed
transversely, faces down perpendicularly to the earth; and it remains only
on its own meridian, or on that which is commonly called the magnetick
meridian.

* * * * *

CHAP. IX.

Demonstration of direction, or of variation from the
_true direction, at the same time with declination, by_
means of only a single motion in water, due
_to the disposing and rotating virtue._

[Illustration]

Fix a slender iron wire of three digits length through * a round cork, so
that the cork may support the iron in water. Let this water be in a
good-sized glass vase or bowl. Pare the round cork little by little with a
very sharp knife (so that it may remain round), until it will stay
motionless one or two digits below the face of the water; and let the wire
be evenly balanced. {203} [239]Rub one end of the wire thus prepared on the
boreal end of a loadstone and the other on the southern part of the stone
(very skilfully, so that the cork may not be moved ever so little from its
place) and again place it in the water; then the wire will dip with a
circular motion on its own centre below the plane of the horizon, in
proportion to the latitude of the region; and, even while dipping, will
also show the point of variation (the true direction being perturbed). Let
the loadstone (that with which the iron is rubbed) be a strong one, such as
is needed in all experiments on magnetick declination. When the iron, thus
put into the water and prepared by means of the loadstone, has settled in
the dip, the lower end remains at the point of variation on the arc of