But it must be observed, that this island cannot move beyond the
extent of the dominions below, nor can it rise above the height of
four miles. For which the astronomers (who have written large
systems concerning the stone) assign the following reason: that
the magnetic virtue does not extend beyond the distance of four
miles, and that the mineral, which acts upon the stone in the
bowels of the earth, and in the sea about six leagues distant from
the shore, is not diffused through the whole globe, but terminated
with the limits of the king's dominions; and it was easy, from the
great advantage of such a superior situation, for a prince to bring
under his obedience whatever country lay within the attraction of
that magnet.
When the stone is put parallel to the plane of the horizon, the
island stands still; for in that case the extremities of it, being
at equal distance from the earth, act with equal force, the one in
drawing downwards, the other in pushing upwards, and consequently
no motion can ensue.
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