CHAP. V.
An island in Ocean does not change the variation223, as
neither do mines of loadstone.
slands, although they be more magnetick
than the sea, yet do not change the magnetick directions or variations. For since direction is a motion derived from the
power of the whole earth, not from the attraction of any hill but from the disposing and turning power of the whole; so
variation (which is a perturbation of the direction) is an aberration of the real turning power arising from the great
inequalities of the earth, in consequence of which it, of itself, slightly diverts movable magneticks toward those which
are the largest and the more powerful. The cause now shown may suffice to explain that which some so wonder at about the
Island of Elba (and although this is productive of loadstone, yet the versorium (or mariners' compass) makes no special
inclination toward it whenever vessels approach it in the Tyrrhenian sea); and the following causes are also to be
considered, viz.: that the virtue of smaller magnetick bodies extends scarcely or not at all of itself beyond their own
mines: for variation does not occur because of attraction, as they would have it who have imagined magnetick poles.
Besides, magnetick mines are only agnate to the true earth, not innate: hence the whole globe does not regard them, and
magneticks are not borne to them, as is demonstrated by the diagram of eminences.