throughout the whole of that meridian. For on the same
meridian * near Brazil something very different occurs, as we will show
further on. The variation (caeteris paribus) is always less near the
aequator, greater in higher latitudes, with the limitation that it be not
very near the pole itself. Hence the variation is greater on the coast of *
Norway and Belgium than on the coast of Morocco or Guinea: greater also
near Cape Race than in the harbours of Norumbega or of Virginia. On the
coast of Guinea magnetick implements deviate by a third part of one rumbe
to the East: in Cape Verde Islands by a half: on the coast of Morocco by
two thirds: in England at the mouth of the Thames by a whole rumbe: and at
London by nearly eleven degrees and one third. For indeed the moving
magnetick virtue is stronger in a higher latitude; and the larger regions
extending toward the poles dominate the more, as is easily apparent
anywhere on a terrella. For as in the case of true Direction magnetick
bodies tend toward the pole (namely, toward the stronger end, the whole
earth causing the motion), so also do they incline a little toward the
stronger and higher parts by the action of the whole along with the
conjoint action of iron bodies.

* * * * *

{155} CHAP. II.

That the variation is caused by the inaequality of the
_projecting parts of the earth_.

Demonstration of this may manifestly be made [Illustration] * by means of a
terrella in the following way: let there be a round loadstone somewhat
imperfect in some part, and impaired by decay (such an one we had with a
certain part corroded to resemble the Atlantick or great Ocean): place upon
it some fine iron wire of the length of two barleycorns, as in the
following figure. A B, a Terrella in certain parts somewhat imperfect and
of unaequal virtue on the circumference. The versoria E, F, do not vary,
but look directly to the pole A; for they are placed in the middle of the
firm and sound part of the terrella and somewhat distant from the imperfect
part: that part of the surface which is distinguished by dots and
transverse lines is the weaker. The versorium O also does not vary (because
it is placed in the middle of the imperfect part), but is directed toward
the pole, {156} just as near the western Azores on the earth. The versoria
H and L do vary, for they incline toward the sounder parts very near them.
As this is manifest in a terrella whose surfac