AN INQUIRY INTO THE CAUSE OF THE NATURAL VIRTUE OF THE LODESTONE
Certain persons who were but poor investigators of nature held the
opinion that the force with which a lodestone draws iron, is found in
the mineral veins themselves from which the stone is obtained; whence
they claim that the iron turns towards the poles of the earth, only
because of the numerous iron mines found there. But such persons are
ignorant of the fact that in many different parts of the globe the
lodestone is found; from which it would follow that the iron needle
should turn in different directions according to the locality; but this
is contrary to experience. Secondly, these individuals do not seem to
know that the places under the poles are uninhabitable because there
one-half the year is day and the other half night. Hence it is most
silly to imagine that the lodestone should come to us from such places.
Since the lodestone points to the south as well as to the north, it is
evident from the foregoing chapters that we must conclude that not only
from the north pole but also from the south pole rather than from the
veins of the mines virtue flows into the poles of the lodestone. This
follows from the consideration that wherever a man may be, he finds the
stone pointing to the heavens in accordance with the position of the
meridian; but all meridians meet in the poles of the world; hence it is
manifest that from the poles of the world, the poles of the lodestone
receive their virtue. Another necessary consequence of this is that the
needle does not point to the pole star, since the meridians do not
intersect in that star but in the poles of the world. In every region,
the pole star is always found outside the meridian except twice in each
complete revolution of the heavens. From all these considerations, it is
clear that the poles of the lodestone derive their virtue from the poles
of the heavens. As regards the other parts of the stone, the right
conclusion is, that they obtain their virtue from the other parts of the
heavens, so that we may infer that not only the poles of the stone
receive their virtue and influence from the poles of the world, but
likewise also the other parts, or the entire stone from the entire
heavens. You may test this in the following manner: A round lodestone on
which the poles are marked is placed on two sharp styles as pivots
having one pivot under each pole so that the lodestone may easily
revolve on these pivots. Having done this, make sure that it is equally
balanced and that it turns smoothly on the pivots. Repeat this several
times at different hours of the day and always with the utmost care.
Then place the stone with its axis in the meridian, the poles resting on
the pivots. Let it be moved after the manner of bracelets so that the
elevation and depression of the poles may equal the elevation and
depressions of the poles of the heavens of the place in which you are
experimenting. If now the stone be moved according to the motion of the
heavens, you will be delighted in having discovered such a wonderful
secret; but if not, ascribe the failure to your own lack of skill rather
than to a defect in nature. Moreover, in this position I consider the
strength of the lodestone to be best preserved. When it is placed
differently, i. e., not in the meridian, I think its virtue is weakened
or obscured rather than maintained. With such an instrument you will
need no timepiece, for by it you can know the ascendant at any hour you
please, as well as all other dispositions of the heavens which are
sought for by astrologers.
PART II
PART II
CHAPTER I
THE CONSTRUCTION OF AN INSTRUMENT FOR MEASURING THE AZIMUTH OF THE SUN
THE MOON OR ANY STAR ON THE HORIZON
Having fully examined all the properties of the lodestone and the
phenomena connected therewith, let us now come to those instruments
which depend for their operation on the knowledge of those facts. Take a
rounded lodestone,[4] and after determining its poles in the manner
already mentioned, file its two sides so that it becomes elongated at
its poles and occupies less space. The lodestone prepared in this wise
is then enclosed within two capsules after the fashion of a mirror. Let
these capsules be so joined together that they cannot be separated and
that water cannot enter; they should be made of light wood and fastened
with cement suited to the purpose. Having done this, place them in a
large vessel of water on the edges of which the two parts of the world,
i. e., the north and south points, have been found and marked. These
points may be united by a thread stretched across from north to south.
Then float the capsules and place a smooth strip of wood over them in
the manner of a diameter. Move the strip until it is equally distant
from the meridian-line, previously determined and marked by a thread, or
else until it coincides therewith. Then mark a line on the capsules
according to the position of the strip, and this will indicate forever
the meridian of that place. Let this line be divided at its middle by
another cutting it at right angles, which will give the east and west
line; thus the four cardinal points will be determined and indicated on
the edge of the capsules. Each quarter is to be subdivided into 90
parts, making 360 in the circumference of the capsules. Engrave these
divisions on them as usually done on the back of an astrolabe. On the
top or edge of the capsules thus marked place a thin ruler like the
pointer on the back of the astrolabe; instead of the sights attach two
perpendicular pins, one at each end. If, therefore, you desire to take
the azimuth of the sun, place the capsules in water and let them move
freely until they come to rest in their natural position. Hold them
firmly in one hand, while with the other you move the ruler until the
shadow of the pins falls along the length of the ruler; then the end of
the ruler which is towards the sun will indicate the azimuth of the sun.
Should it be windy, let the capsules be covered with a suitable vessel
until they have taken their position north and south. The same method,
namely, by sighting, may be followed at night for determining the
azimuth of the moon and stars; move the ruler until the ends of the pins
are in the same line with the moon or star; the end of the ruler will
then indicate the azimuth just as in the case of the sun. By means of
the azimuth may then be determined the hour of the day, the ascendant,
and all those other things usually determined by the astrolabe. A form
of the instrument is shown in the following figure.
[Illustration: FIG. 1.—AZIMUTH COMPASS]
CHAPTER II
THE CONSTRUCTION OF A BETTER INSTRUMENT FOR THE SAME PURPOSE
In this chapter I will describe the construction of a better and more
efficient instrument. Select a vessel of wood, brass or any solid
material you like, circular in shape, moderate in size, shallow but of
sufficient width, with a cover of some transparent substance, such as
glass or crystal; it would be even better to have both the vessel and
the cover transparent. At the centre of this vessel fasten a thin axis
of brass or silver, having its extremities in the cover above and the
vessel below. At the middle of this axis let there be two apertures at
right angles to each other; through one of them pass an iron stylus or
needle, through the other a silver or brass needle crossing the iron one
at right angles. Divide the cover first into four parts and subdivide
these into 90 parts, as was mentioned in describing the former
instrument. Mark the parts north, south, east and west. Add thereto a
ruler of transparent material with pins at each end. After this bring
either the north or the south pole of a lodestone near the cover so that
the needle may be attracted and receive its virtue from the lodestone.
Then turn the vessel until the needle stands in the north and south line
already marked on the instrument; after which turn the ruler towards the
sun if day-time, and towards the moon and stars at night, as described
in the preceding chapter. By means of this instrument you can direct
your course towards cities and islands and any other place wherever you
may wish to go by land or sea, provided the latitude and longitude of
the places are known to you. How iron remains suspended in air by virtue
of the lodestone, I will explain in my book on the action of mirrors.
Such, then, is the description of the instrument illustrated below. (See
Figs. 2 and 3.)
[Illustration: FIG. 2.—DOUBLE-PIVOTED NEEDLE]
[Illustration: FIG. 3.—PIVOTED COMPASS]
CHAPTER III
THE ART OF MAKING A WHEEL OF PERPETUAL MOTION
In this chapter I will make known to you the construction of a wheel
which in a remarkable manner moves continuously. I have seen many
persons vainly busy themselves and even becoming exhausted with much
labor in their endeavors to invent such a wheel. But these invariably
failed to notice that by means of the virtue or power of the lodestone
all difficulty can be overcome. For the construction of such a wheel,
take a silver capsule like that of a concave mirror, and worked on the
outside with fine carving and perforations, not only for the sake of
beauty, but also for the purpose of diminishing its weight. You should
manage also that the eye of the unskilled may not perceive what is
cunningly placed inside. Within let there be iron nails or teeth of
equal weight fastened to the periphery of the wheel in a slanting
direction, close to one another so that their distance apart may not be
more than the thickness of a bean or a pea; the wheel itself must be of
uniform weight throughout. Fasten the middle of the axis about which the
wheel revolves so that the said axis may always remain immovable. Add
thereto a silver bar, and at its extremity affix a lodestone placed
between two capsules and prepared in the following way: When it has been
rounded and its poles marked as said before, let it be shaped like an
egg; leaving the poles untouched, file down the intervening parts so
that thus flattened and occupying less space, it may not touch the sides
of the capsules when the wheel revolves. Thus prepared, let it be
attached to the silver rod just as a precious stone is placed in a ring;
let the north pole be then turned towards the teeth or cogs of the wheel
somewhat slantingly so that the virtue of the stone may not flow
diametrically into the iron teeth, but at a certain angle; consequently
when one of the teeth comes near the north pole and owing to the impetus
of the wheel passes it, it then approaches the south pole from which it
is rather driven away than attracted, as is evident from the law given
in a preceding chapter. Therefore such a tooth would be constantly
attracted and constantly repelled.
[Illustration: FIG. 4.—PERPETUAL MOTION WHEEL]
In order that the wheel may do its work more speedily, place within the
box a small rounded weight made of brass or silver of such a size that
it may be caught between each pair of teeth; consequently as the
movement of the wheel is continuous in one direction, so the fall of the
weight will be continuous in the other. Being caught between the teeth
of a wheel which is continuously revolving, it seeks the centre of the
earth in virtue of its own weight, thereby aiding the motion of the
teeth and preventing them from coming to rest in a direct line with the
lodestone. Let the places between the teeth be suitably hollowed out so
that they may easily catch the body in its fall, as shown in the diagram
above. (Fig. 4.)
Farewell: finished in camp at the siege of Lucera on the eighth day of
August, Anno Domini MCCLXIX.
NOTES
EARLY REFERENCES TO THE MARINER’S COMPASS
The following are the passages referred to in the introductory notice:
Abbot Neckam (1157-1217), in his _De Naturis Rerum_, writes:
“The sailors, moreover, as they sail over the sea, when in cloudy
weather they can no longer profit by the light of the sun, or when the
world is wrapped up in the darkness of the shades of night and they are
ignorant to what point their ship’s course is directed, these mariners
touch the lodestone with a needle, which (the needle) is whirled round
in a circle until when its motion ceases, its point looks direct to the
north. (_Cuspis ipsius septentrionalem plagam respiciat._)”
In his _De Utensilibus_, we read:
“Among other stores of a ship, there must be a needle mounted on a dart
(_habeat etiam acum jaculo superpositam_) which will oscillate and turn
until the point looks to the north, and the sailors will thus know how
to direct their course when the pole star is concealed through the
troubled state of the atmosphere.”[5]
Alexander Neckam was born at St. Albans in 1157, joined the Augustinian
Order and taught in the University of Paris from 1180 to 1187, after
which he returned to England to take charge of a College of his Order at
Dunstable. He was elected Abbot of Cirencester in 1213 and died at
Kemsey, near Worcester, in 1217.
The satirical poem of Guyot de Provins, written about 1208, contains the
following passage:
The mariners employ an art which cannot deceive,
By the property of the lodestone,
An ugly stone and brown,
To which iron joints itself willingly
They have; they attend to where it points
After they have applied a needle to it;
And they lay the latter on a straw
And put it simply in the water
Where the straw makes it float.
Then the point turns direct
To the star with such certainty
That no man will ever doubt it,
Nor will it ever go wrong.
When the sea is dark and hazy,
That one sees neither star nor moon,
Then they put a light by the needle
And have no fear of losing their way.
The point turns towards the star;
And the mariners are taught
To follow the right way.
It is an art which cannot fail.
Provins, from which Guyot took his surname, was a small town in the
vicinity of Paris.
Cardinal Jacques de Vitry, in his _Historia Orientalis_, Cap. 89,
writes:
“An iron needle, after having been in contact with the lodestone, turns
towards the north star, so that it is very necessary for those who
navigate the seas.”
Jacques de Vitry was born at Argenteuil, near Paris, joined the fourth
crusade, became Bishop of Ptolemais, and died in Rome in 1244. He wrote
his “Description of Palestine,” which forms the first book of his
_Historia Orientalis_, in the East, between 1215 and 1220.
Albertus Magnus (1193-1280) in his _De Mineralibus_, Lib. II., Tract 3,
Cap. 6, writes:
“It is the end of the lodestone which makes the iron that touched it
turn to the north (_ad zoron_) and which is of use to mariners; but the
other end of the needle turns toward the south (_ad aphron_).”
This illustrious Bavarian schoolman joined the Dominican Order in his
youth, lectured to great audiences in Cologne, became bishop of
Ratisbonne in 1260, and died in 1280. Thomas Aquinas the greatest of
schoolmen, was among his pupils.
In the Spanish code of laws, begun in 1256, during the reign of Alfonso
el Sabio, and known as _Las Siete Partidas_, we read:
“Just as mariners are guided during the night by the needle, which
replaces for them the shores and pole star alike, by showing them the
course to pursue both in fair weather and foul, so those who are called
upon to advise the King must always be guided by a spirit of justice.”
Brunetto Latini, in his _Trésor des Sciences_, 1260, writes:
“The sailors navigate the seas guided by the two stars called the
tramontanes, and each of the two parts of the lodestone directs the end
of the needle to the star to which that part itself turns.”
Brunetto Latini (1230-1294) was a man of great eminence in the
thirteenth century; Dante was among his pupils at Florence. For
political reasons, he removed to Paris, where he wrote his _Trésor_ and
also his _Tesoretto_. He visited Roger Bacon at Oxford about 1260.
In his treatise _De Contemplatione_, begun in 1272, Raymond Lully
writes:
“As the needle, after having touched the lodestone, turns to the north,
so the mariner’s needle (_acus nautica_) directs them over the sea.”
Lully was born at Palma in the Island of Majorca in 1236; he joined the
Third Order of St. Francis, dying in 1315.
Ristoro d’Arezzo, in his _Libro della Composizione del Mundo_, written
in 1282, has the following:
“Besides this, there is the needle which guides the mariner, and which
is itself directed by the star called the tramontane.”[6]
The following metrical translation of a poem by Guido Guinicelli, an
Italian priest, 1276, is from the pen of Dr. Park Benjamin, of New York:
In what strange regions ’neath the polar star
May the great hills of massy lodestone rise,
Virtue imparting to the ambient air
To draw the stubborn iron; while afar
From that same stone, the hidden virtue flies
To turn the quivering needle to the Bear
In splendor blazing in the Northern skies.
The above extracts show that the directive property of the magnetic
needle was well known in England, France, Germany, Spain and Italy in
the thirteenth century. In the passage from Neckam, the _acum jaculo
superpositam_ has been construed by some to mean a form of pivoted
needle, while in the letter of Peregrinus, 1269, the double pivoted form
is clearly described.
Footnotes
[1]With very few exceptions all the works referred to in this notice
will be found in the Wheeler Collection in the Library of the
American Institute of Electrical Engineers, New York.
[2]It is probable that Flavio Gioja, an Italian pilot, some fifty years
later, added the compass-card and attached it to the magnet.
[3]Annali di Matematica Pura ed Applicata, 1865.
[4]A terrella, or earthkin.
[5]The Chronicles and Memoirs of Great Britain and Ireland during the
Middle Ages, by Thomas Wright (1863).
[6]The pole-star was thus named in the south of France and the north of
Italy because seen beyond the mountains (the Alps).
Transcriber’s Notes
—Retained publication and copyright information from the original; this
eBook is public-domain in the U.S.
—Silently corrected a few palpable typographical errors.
—In the text versions, enclosed italicized text in _underscore_.