Magnet Stone, of what kind it is, and its
_discovery._
Loadstone, the stone which is commonly called the Magnet, derives its name
either from the discoverer (though he was not Pliny's fabulous
herdsman[48], quoted from Nicander, the nails of whose shoes and the tip of
whose staff stuck fast in a magnetick field while he pastured his flocks),
or from the region of Magnesia in Macedonia, rich in loadstones: Or else
from the city Magnesia in Ionia in Afia Minor, near the river Mæander.
Hence Lucretius says,
_The Magnet's name the observing Grecians drew_
_From the Magnetick region where it grew._
It is called Heraclean from the city Heraclea, or from the invincible
Hercules, on account of the great strength and domination and power which
there is in iron of subduing all things: it is also called _siderite_, as
being of iron; being not unknown to the most ancient writers, to the
Greeks, Hippocrates, and others, as also (I believe) to Jewish and Egyptian
writers; For in the oldest mines of iron, the most famous in Asia, the
loadstone was often dug out with its uterine brother, iron. And if the
tales be true which are told of the people of the Chinas, they were not
unacquainted in primitive times with magnetical experiments, for even
amongst {9} them the finest magnets of all are still found. The Egyptians,
as Manetho relates, gave it the name Os Ori: calling the power which
governs the turning of the sun Orus, as the Greeks call it Apollo. But
later by Euripides, as narrated by Plato, it was designated under the name
of Magnet. By Plato in the _Io_, Nicander of Colophon, Theophrastus,
Dioscorides, Pliny, Solinus, Ptolemy, Galen, and other investigators of
nature it was recognized and commended; such, however, is the variety of
magnets and their points of unlikeness in hardness, softness, heaviness,
lightness, density, firmness, and friability of substance: so great and
manifold are the differences in colour and other qualities, that they have
not handed down any adequate account of it, which therefore was laid aside
or left imperfect by reason of the unfavourable character of the time; for
in those times varieties of specimens and foreign products never before
seen were not brought from such distant regions by traders and mariners as
they have been lately, and now that all over the globe all kinds of
merchandise, stones, woods, spices, herbs, metals, and ore in abundance are
greedily sought after: neither was metallurgy so generally cultivated in a
former age. There is a difference in vigour; as whether it is male or
female: for it was thus that the ancients used often to distinguish many
individuals of the same species. Pliny quotes from Sotacus five kinds;
those from Æthiopia, Macedonia, Boeotia, the Troad, and Asia, which were
especially known to the ancients: but we have posited as many kinds of
loadstones as there are in the whole of nature regions of different kinds
of soil. For in all climates, in every province, on every soil, the
loadstone is either found, or else lies unknown on account of its rather
deep site and inaccesible position; or by reason of its weaker and less
obvious strength it is not recognized by us while we see and handle it. To
the ancients the differences were those of colour[49], how they are red and
black in Magnesia and Macedonia, in Boeotia red rather than black, in the
Troad black, without strength: While in Magnesia in Asia they are white,
not attracting iron, and resemble pumice-stone. A strong loadstone of the
kind celebrated so often nowadays in experiments presents the appearance of
unpolished iron, and is mostly found in iron mines: it is even wont to be
discovered in an unbroken lode by itself: Loadstones of this sort are
brought from East India, China, and Bengal, of the colour of iron, or of a
dark blood or liver colour; and these are the finest, and are sometimes of
great size, as though broken off a great rock, and of considerable weight;
sometimes single stones, as it were, and entire: some of these, though of
only one pound weight, can lift on high four ounces of iron or a half-pound
or even a whole pound. Red ones are found in Arabia, as broad as a tile,
not equal in weight to those brought from China, but strong and good: they
are a little darker in the island of Elba in the Tuscan sea, and together
with {10} these also grow white ones, like some in Spain in the mines of
Caravaca: but these are of lesser power. Black ones also are found, of
lower strength, such as those of the iron mines in Norway and in sea-coast
places near the strait of Denmark. Amongst the blue-black or dusky blue
also some are strong and highly commended. Other loadstones are of a leaden
colour, fissile and not-fissile, capable of being split like slates in
layers. I have also some like gray marble of an ashen colour, and some
speckled like gray marble, and these take the finest polish. In Germany
there are some perforated like honeycombs, lighter than any others, and yet
strong. Those are metallick which smelt into the best iron; others are not
easily smelted, but are burned up. There are loadstones that are very
heavy, as also others very light; some are very powerful in catching up
pieces of iron, while others are weaker and of less capacity, others so
feeble and barren that they with difficulty attract ever so tiny a piece of
iron and cannot repel an opposite magnetick. Others are firm and tough, and
do not readily yield to the artificer. Others are friable. Again, there are
some dense and hard as emery, or loose-textured and soft as pumice; porous
or solid; entire and uniform, or varied and corroded; now like iron for
hardness, yea, sometimes harder than iron to cut or to file; others are as
soft as clay. Not all magnets can be properly called stones; some rather
represent rocks; while others exist rather as metallick lodes; others as
clods and lumps of earth. Thus varied and unlike each other, they are all
endowed, some more, some less, with the peculiar virtue. For they vary
according to the nature of the soil, the different admixture of clods and
humours, having respect to the nature of the region and to their subsidence
in this last-formed crust of the earth, resulting from the confluence of
many causes, and the perpetual alternations of growth and decline, and the
mutations of bodies. Nor is this stone of such potency rare; and there is
no region wherein it is not to be found in some sort. But if men were to
search for it more diligently and at greater outlay, or were able, where
difficulties are present, to mine it, it would come to hand everywhere, as
we shall hereafter prove. In many countries have been found and opened
mines of efficacious loadstones unknown to the ancient writers, as for
instance in Germany, where none of them has ever asserted that loadstones
were mined. Yet since the time when, within the memory of our fathers,
metallurgy began to flourish there, loadstones strong and efficacious in
power have been dug out in numerous places; as in the Black Forest beyond
Helceburg; in Mount Misena not far from Schwartzenberg[50]; a fairly strong
kind between Schneeberg and Annaberg in Joachimsthal, as was noticed by
Cordus: also near the village of Pela in Franconia. In Bohemia it occurs in
iron mines in the Lessa district and other places, as Georgious Agricola
and several other men learned in metallurgy {11} witness. In like manner in
other countries in our time it is brought to light; for as the stone
remarkable for its virtues is now famous throughout the whole world, so
also everywhere every land produces it, and it is, so to speak, indigenous
in all lands. In East India, in China, in Bengal near the river Indus it is
common, and in certain maritime rocks: in Persia, Arabia, and the islands
of the Red Sea; in many places in Æthiopia, as was formerly Zimiri, of
which Pliny makes mention. In Asia Minor around Alexandria and the Troad;
in Macedonia, Boeotia, in Italy, the island of Elba, Barbary; in Spain
still in many mines as aforetime. In England quite lately a huge power of
it was discovered in a mine belonging to Adrian Gilbert, gentleman[51];
also in Devonshire and the Forest of Dean; in Ireland, too, Norway,
Denmark, Sweden, Lapland, Livonia, Prussia, Poland, Hungary. For although
the terrestrial globe, owing to the varied humours and natures of the soil
arising from the continual succession of growth and decay, is in the lapse
of time efflorescing through all its ambit deeper into its surface, and is
girt about with a varied and perishable covering, as it were with a veil;
yet out of her womb ariseth in many places an offspring nigher to the more
perfect body and makes its way to the light of day. But the weak and less
vigorous loadstones, enfeebled by the flow of humours, are visible in every
region, in every strath. It is easy to discover a vast quantity of them
everywhere without penetrating mountains or great depths, or encountering
the difficulties and hardships of miners; as we shall prove in the sequel.
And these we shall take pains so to prepare by an easy operation that their
languid and dormant virtue shall be made manifest. It is called by the
Greeks[52] [Greek: heraklios], as by Theophrastus, and [Greek: magnêtis];
and [Greek: magnês], as by Euripides, as quoted by Plato in the _Io_: by
Orpheus[53] too [Greek: magnêosa], and [Greek: sideritês] as though of
iron: by the Latins _magnes_, _Herculeus_; by the French _aimant_[54],
corruptly from _adamant_; by the Spaniards _piedramant_: by the Italians
_calamita_[55]; by the English LOADSTONE and ADAMANT STONE[56], by the
Germans _magness_[57] and _siegelstein_: Among English, French, and
Spaniards it has its common name from adamant; perhaps because they were at
one time misled by the name _sideritis_ being common to both: the magnet is
called [Greek: sideritês] from its virtue of attracting iron: the adamant
is called [Greek: sideritês] from the brilliancy of polished iron.
Aristotle designates it merely by the name of _the stone_:[58] [Greek:
Eoike de kai thalês ex hôn apomnêmoneuousi, kinêtikon ti tên psuchên
hupolabein, eiper ton lithon ephê psuchên echein, hoti ton sidêron kinei]:
_De Anima_, Lib. I. The name of magnet is also applied to another stone
differing from siderite, having the appearance of silver; it is like
Amianth in its nature; and since it consists of laminæ (like specular
stone)[59], it differs in form: in German _Katzensilber_ and _Talke_[60].
* * * * *
{12} CHAP. III.
The Loadstone has parts distinct in their natural
_power, & poles conspicuous for their property._
The stone itself manifests many qualities which, though known afore this,
yet, not having been well investigated, are to be briefly indicated in the
first place so that students may understand the powers of loadstone and
iron, and not be troubled at the outset through ignorance of reasonings and
proofs. In the heaven astronomers assign a pair of poles for each moving
sphere: so also do we find in the terrestrial globe natural poles
preeminent in virtue, being the points that remain constant in their
position in respect to the diurnal rotation, one tending to the Bears and
the seven stars; the other to the opposite quarter of the heaven. In like
manner the loadstone has its poles, by nature northern and southern, being
definite and determined points set in the stone, the primary boundaries of
motions and effects, the limits and governors of the many actions and
virtues. However, it must be understood that the strength of the stone does
not emanate from a mathematical point, but from the parts themselves, and
that while all those parts in the whole belong to the whole, the nearer
they are to the poles of the stone the stronger are the forces they acquire
and shed into other bodies: these poles are observant of the earth's poles,
move toward them, and wait upon them. Magnetick poles can be found in every
magnet, in the powerful and mighty (which Antiquity used to call the
masculine) as well as in the weak, feeble and feminine; whether its figure
is due to art or to chance, whether long, flat, square, three-cornered,
polished; whether rough, broken, or unpolished; always the loadstone
contains and shows its poles. * But since the spherical form, which is also
the most perfect, agrees best with the earth, being a globe, and is most
suitable for use and experiment, we accordingly wish our principal
demonstrations by the stone to be made with a globe-shaped magnet as being
more perfect and adapted for the purpose. Take, then, a powerful loadstone,
solid, of a just size, uniform, hard, without flaw[61]; make of it a globe
upon the turning tool used for rounding crystals and some other stones, or
with other tools as the material and firmness of the stone requires, for
sometimes it is difficult to be worked. The stone thus perpared is a true,
homogeneous offspring of the earth and of the same shape with it:
artificially possessed of the orbicular form which nature granted from the
beginning to the common mother earth: and it is a physical corpuscle imbued
with many virtues, by {13} means of which many abstruse and neglected
truths in philosophy buried in piteous darkness may more readily become
known to men. This round stone is called by us a [Greek: mikrogê] or
_Terrella_[62]. To find, then, the poles conformable to the earth's, take
the round stone in hand, and place upon the stone a needle or wire of iron:
the ends of the iron move upon their own centre and suddenly stand still.
Mark the stone with ochre or with chalk where the wire lies and sticks:
move the middle or centre of the wire to another place, and so on to a
third and a fourth, always marking on the stone along the length of the
iron where it remains at rest: those lines show the meridian circles, or
the circles like meridians on the stone, or terrella, all of which meet as
will be manifest at the poles of the stone. By the circles thus continued
the poles are made out, the Boreal as well as the southern, and in the
middle space betwixt these a great circle may be drawn for an æquator, just
as Astronomers describe them in the heavens and on their own globes, or as
Geographers do on the terrestrial globe: for that line so drawn on this our
terrella is of various uses in our demonstrations and experiments
magnetical. Poles are also found in a round stone by a versorium, a piece
of iron touched with a loadstone, and placed upon a needle or point firmly
fixed on a foot so as to turn freely about in the following way:[63]
[Illustration]
On the stone A B the versorium is placed in such a way that the versorium
may remain in equilibrium: you will mark with chalk the course of the iron
when at rest: Move the instrument to another spot, and again make note of
the direction and aspect: do the same thing in several places, and from the
concurrence of the lines of direction you will find one pole at the point
A, the other at B. A versorium placed near the stone also indicates the
true pole; when at right angles it eagerly beholds the stone and seeks the
pole itself directly, and is turned in a straight line through the axis to
the {14} centre of the stone. For instance, the versorium D faces toward A
and F, the pole and centre, whereas E does not exactly respect * either the
pole A or the centre F[64]. A bit of rather fine iron wire, of the length
of a barley-corn, is placed on the stone, and is moved over the regions and
surface of the stone, until it rises to the perpendicular[65]: for it
stands erect at the actual pole, whether Boreal or austral; the further
from the pole, the more it inclines from the vertical. The poles thus found
you shall mark with a sharp file or gimlet.
* * * * *