HOW TO DISCOVER THE POLES OF A LODESTONE AND HOW TO TELL WHICH IS NORTH
AND WHICH SOUTH
The poles of a lodestone having been located in a general way, you will
determine which is north and which south in the following manner: Take a
wooden vessel rounded like a platter or dish, and in it place the stone
in such a way that the two poles will be equidistant from the edge of
the vessel; then place the dish in another and larger vessel full of
water, so that the stone in the first-mentioned dish may be like a
sailor in a boat. The second vessel should be of considerable size so
that the first may resemble a ship floating in a river or on the sea. I
insist upon the larger size of the second vessel in order that the
natural tendency of the lodestone may not be impeded by contact of one
vessel against the sides of the other. When the stone has been thus
placed, it will turn the dish round until the north pole lies in the
direction of the north pole of the heavens, and the south pole of the
stone points to the south pole of the heavens. Even if the stone be
moved a thousand times away from its position, it will return thereto a
thousand times, as by natural instinct. Since the north and south parts
of the heavens are known, these same points will then be easily
recognized in the stone because each part of the lodestone will turn to
the corresponding one of the heavens.