BOOK THIRD.
CHAP. I.
ON DIRECTION.
n referring to the earlier books it will
be found shown that a loadstone has its poles, and that a piece of iron has also poles, and rotation, and a certain
verticity; finally, that the loadstone and the iron direct their poles toward the poles of the earth. Now, however, we
must make clear the causes of these things and their admirable workings, pointed out indeed before, but not proven. All
those who have written before us about these rotations have left us their opinions so briefly, so meagrely, and with such
hesitating judgment that they seem hardly likely ever to persuade anyone, or even to be able to satisfy themselves; and
all their petty reasons are rejected by the more prudent as useless, uncertain, and absurd, being supported by no proofs
or arguments; whence also magnetick science, being all the more neglected and not understood, has been in exile. The true
austral pole of a loadstone, not the boreal (as all before us used to think), * if the loadstone is placed in its boat on the
surface of water, turns to the North; in the case of a piece of iron also, whether it has been excited by a loadstone or
not, the southern end moves toward the North. An oblong piece of iron of three or four digits' length196, when skilfully rubbed with a loadstone, quickly turns north and south. Wherefore
mechanicians, taking a piece of iron prepared in this way, balance it on a pin in a box, and fit it up with the
requisites of a sun-dial; or they prepare the versorium out of two curved pieces of iron with their ends touching one
another, so that the motion may be more constant. In this way the mariners' versorium is arranged, which is an instrument
beneficial, useful, and auspicious to sailors for indicating, like a good genius, safety and the right way. But it must
be understood on the threshold of this argument (before we proceed further) that these pointings of the loadstone or of
iron are not perpetually made toward the true poles of the world, do not always seek those fixed and definite
points, or remain on the line of the true meridian; but usually diverge some distance to the East or to the West.
Sometimes also at certain places on land or sea they do indicate exactly the true poles. This discrepancy is called the
Variation of the iron or of the loadstone; and since this is brought about by other causes, and is merely a
certain disturbance and perversion of the true direction, we are directing our attention in this place to the true
direction of the compass and of the magnetick iron (which would be equally toward the true poles and on the true meridian
everywhere on the earth, unless other obstacles and an untoward pervertency hindered it). Of its variation and the cause
of the perversion we shall treat in the next book. Those who wrote about the world and about natural philosophy a century
ago, especially those remarkable elementary philosophers, and all those who trace their knowledge and training to them
down to our own times, those men, I say, who represented the earth as always at rest and, as it were, a useless weight,
placed in the centre of the universe at an equal distance from the sky on every side, and its nature to be simple, imbued
only with the qualities of dryness and cold, sought diligently for the causes of all things and of all effects in the
heavens, the stars, the planets, in fire, air, waters and substances of mixed natures. Never indeed did they recognize
that the terrestrial globe had, besides dryness and cold, some special, effective, and predominant properties,
strengthening, directing, and moving the globe itself through its whole mass and its very deepest vitals; nor did they
ever inquire whether there were any such. For this reason the crowd of philosophizers, in order to discover the reasons
of the magnetical motions, called up causes lying remote and far away. And one man seems to me beyond all others worthy
of censure, Martin Cortes, who, since there was no cause which could satisfy him in the whole of nature, dreamed that
there was a point of magnetical attraction beyond the heavens, which attracted iron. Peter Peregrinus thinks that the
direction arises from the poles of the sky. Cardan thought that the turning of iron was caused by a star in the tail of
the Great Bear; Bessard, the Frenchman, opines that a magnetick turns toward the pole of the zodiack. Marsilius Ficinus
will have it that the loadstone follows its own Arctick pole; but that iron follows the loadstone, straws amber; whilst
this perhaps follows the Antarctick pole—a most foolish dream. Others have recourse to I know not what magnetick rocks
and mountains. Thus it is always customary with mortals, that they despise things near home, whilst foreign and distant
things are dear and prized. But we study the earth itself and observe in it the cause of so great an effect. The earth,
as the common mother, has these causes inclosed in her innermost parts; in accordance with her rule, position, condition, verticity, poles, æquator, horizons, meridians, centre, circumference, diameter,
and the nature of the whole interior of her substance, must all magnetical motions be discussed. The earth has been
ordered by the highest Artificer and by nature in such a way that it should have parts dissimilar in position, bounds of
the whole and complete body, ennobled by certain functions, by which it might itself remain in a definite direction. For
just as a loadstone, when it is floated on water in a suitable vessel, or is hung by slender threads in the air, by its
implanted verticity conforms its poles to the poles of the common mother in accordance with magnetick laws; so if the
earth were to deviate from its natural direction and its true position in the universe, or if its poles were to be drawn
aside (if this were possible) toward the sun-rising or the sun-setting or toward any other points whatsoever in the
visible firmament, they would return again to the north and south by magnetical motion, and would settle at the same
points at which they are now fixed. The reason why the terrestrial globe seems to remain more steadily with the one pole
toward those parts and directed toward the Cynosure, and why its pole diverges by 23 degrees 29 minutes, with a certain
variation not sufficiently investigated as yet by Astronomers, from the poles of the ecliptick, depends on its virtue
magnetical. The causes of the precession of the æquinoxes and the progression of the fixed stars, and of the change,
moreover, in the declinations of the sun and of the tropicks, must be sought from magnetick influences; so that neither
that absurd motion of trepidation of Thebit Bencora197, which is at great
variance with observations, nor the monstrous superstructures of other heavens, are any longer needed. A versatory iron
turns to the position of the earth, and if disturbed ever so often returns always to the same points. For in the far
regions of the north, in a latitude of 70 or 80 degrees (to which at the milder seasons of the year our sailors are
accustomed to penetrate without injury from the cold); in the regions halfway between the poles; on the æquator in the
torrid zone; and again in all the maritime places and lands of the south, in the highest latitude which has thus far been
reached, always the iron magnetick finds its way, and points to the poles in the same manner (excepting for the
difference of variation); on this side of the æquator (where we live), and on the other side to the south, less well
known, but yet in some measure explored by sailors: and always the lily of the compass points toward the North. This we
have had confirmed by the most eminent captains, and also by very many of the more intelligent sailors. These facts have
been pointed out to me and confirmed by our most illustrious Sea-god, Francis Drake, and by another circumnavigator of
the globe, Thomas Candish; our terrella also indicates the same thing. This is demonstrated in the case of the 
orbicular stone, whose
poles are A and B; an iron wire CD, which is placed upon the stone, always points directly along the meridian toward the
poles AB, whether the centre of the wire is on the central line or æquator of the stone, or on any other part situated
between the æquator and the poles, as at H, G, F, E. So the cusp of a versorium on this side of the æquator points toward
the north; * on the other side the
cross is always directed toward the south; but the cusp or lily198 does not,
as some one has thought, turn toward the south beyond the æquator. Some inexperienced people indeed, who in distant parts
beyond the æquator have seen the versorium sometimes become more sluggish and less prompt, thought that the distance from
the arctick pole or from the magnetick rocks was the cause of this. But they are very much mistaken; for it is as
powerful199, and adjusts itself as quickly to the meridian or to the point of
variation in the southern as in the northern parts of the earth. Yet sometimes the motion appears slower, namely, when
the supporting pin by lapse of time and long voyaging has become somewhat blunt, or the magnetick iron parts have lost,
by age or rust, some of their acquired vigour. This may also be shown experimentally by the versatory iron of a small
sun-dial placed on a very short pin set perpendicular to the surface of the stone, for the iron when touched by a
loadstone points toward the poles of the stone and leaves the poles of the earth; for the general and remoter cause is
overcome by the particular and powerful cause which is so near at hand. Magnetick bodies have of themselves an
inclination toward the position of the earth and are influenced by a terrella. Two equal stones of equal strength adjust
themselves to a terrella in accordance with magnetick laws. The iron conceives vigour from the loadstone and is
influenced by the magnetical motions. Wherefore true direction is the motion of a magnetick body in regard to the
verticity of the earth, the natures of both agreeing and working together toward a natural position and unity. For indeed
we have found out at length, by many experiments and in many ways, that there is a disposing nature, moving them together
by reason of their various positions by one form that is common to both, and that in all
magnetick substances there is attraction and repulsion. For both the stone200
and the magnetick iron arrange themselves by inclination and declination, according to the common position of their
nature and the earth. And the force of the earth by the virtue of the whole, by attracting toward the poles, and
repelling, arranges all magneticks which are unfixed and loose. For in all cases all magneticks conform themselves to the
globe of the earth in the same ways and by the same laws by which another loadstone or any magneticks do to a
terrella.201