vated lands is more vigorous, for
the virtue flows from the whole globe, and since also the causes of
variation are nearer, therefore the versorium deflects the more from its
true direction toward those eminences. It must also be known that the
direction of the versorium on its pin along the plane of the Horizon is
much stronger at the aequator than anywhere else by reason of the
disposition of the {169} versorium; and this direction falls off with an
increase of latitude. For on the aequator the versorium is, following its
natural property, directed along the plane of the horizon; but in other
places it is, contrary to its natural property, compelled into
aequilibrium, and remains there, compelled by some external force: because
it would, according to its natural property, dip below the horizon in
proportion to the latitude, as we shall demonstrate in the book _On
Declination_. Hence the direction falls off and at the pole is itself
nothing: and for that reason a feebler direction is easily vanquished by
the stronger causes of variation, and near the pole the versorium deflects
the more from the meridian. It is demonstrated by means of a terrella: if
an iron wire of two digits length be placed on its aequator, it will be
strongly and rapidly directed toward the poles along the meridian, but more
weakly so in the mid-intervals; while near the poles one may discern a
precipitate variation.

* * * * *

CHAP. XI.

Cardan's error when he seeks the distance of the
_centre of the earth from the centre of the cosmos by the_
motion of the stone of Hercules; in his
_book 5, On Proportions_.

One may very easily fall into mistakes and errors when one is searching
into the hidden causes of things, in the absence of real experiments, and
this is easily apparent from the crass error of Cardan; who deems himself
to have discovered the distances of the centres of the cosmos and of the
earth through a variation of the magnetick iron of 9 degrees. For he
reckoned that everywhere on the earth the point of variation on the Horizon
is always distant nine degrees from the true north, toward the east: and
from thence he forms, by a most foolish error, his demonstrative ratio of
the separate centres.

* * * * *

{170} CHAP. XII.

On the finding of the amount of variation: how great
_is the arc of the Horizon from its arctick or antarctick_
intersection of the meridian