On 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' length[196], 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 {116} 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, {117}
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 Bencora[197], 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 {118} [Illustration] 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 lily[198] 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 powerful[199], 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
{119} to both, and that in all magnetick substances there is attraction and
repulsion. For both the stone[200] 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]
* * * * *