Why in various places near the pole the variations
are much more ample than in a
_lower latitude_.
Variations are often slight, and generally null, when the versorium is at
or near the earth's æquator. In a higher Latitude of 60, 70 or 80 deg.
there are not seldom very wide variations. The cause of this is to be
sought partly from the nature of the earth and partly from the disposition
of the versorium. The earth turns magnetick bodies and at the æquator
directs them strongly toward the pole: [227]at the poles there is no
direction, but only a strong coition through the congruent poles. Direction
is therefore weaker near the poles, because by reason of its own natural
tendency to turn, the versorium dips very much, and is not strongly
directed. But since the force of those elevated 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 æquator 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 æquator 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 æquilibrium,
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 æquator, 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.
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