The letter of Petrus Peregrinus on the magnet, A.D. 1269

THE LETTER OF
P E T R U S

PEREGRINUS

ON THE MAGNET, A,D. I2,6p

LETTER OF

PETRUS PEREGRINUS

ON THE MAGNET

A.D. 1269

THE LETTER OF
P E T R U S

PEREGRINUS

ON THE MAGNET, A.D. 1269

TRANSLATED BY

BROTHER ARNOLD, M.Sc.

PRINCIPAL OF LA SALLE INSTITUTE, TROY
WITH

INTRODUCTORY NOTICE

BY

BROTHER POTAMIAN, D.Sc.

PROFESSOR OF PHYSICS IN MANHATTAN
COLLEGE, NEW YORK

NEW YORK

McGRAW PUBLISHING COMPANY
MCMIV

Copyright, 1904, by
McGRAw PUBLISHING COMPANY

INTRODUCTORY

5KLr
URL

5140247

THE magnetic lore of classic antiquity was
scanty indeed, being limited to the at-
traction which the lodestone manifests
for iron. Lucretius (99-55 B. C.), however, in
his poetical dissertation on the magnet, contained
in De Rerum Natura, Book VI.1 recognizes mag-
netic repulsion, magnetic induction, and to some
extent the magnetic field with its lines of force,
for in verse 1 040 he writes :

Oft from the magnet, too, the steel recedes,
Repelled by turns and re-attracted close.

And in verse 1085 :

Its viewless, potent virtues men surprise ;

Its strange effects, they view with wond'ring eyes

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 In-
stitute of Electrical Engineers, New York.

THE LETTER OF PEREGRINUS

When without aid of hinges, links or springs

A pendant chain we hold of steely rings

Dropt from the stone — the stone the binding source —

Ring cleaves to ring and owns magnetic force :

Those held above, the ones below maintain,

Circle 'neath circle downward draws in vain

Whilst free in air disports the oscillating chain.

The poet Claudian (365-408 A. D.) wrote a
short idyll on the attractive virtue of the lode-
stone and its symbolism ; St. Augustine (354-
430), in his work De Civitate Dei, records the
fact that a lodestone, held under a silver plate,
draws after it a scrap of iron lying on the plate.
Abbot Neckam, the Augustinian (1157-1217),
distinguishes between the properties of the two
ends of the lodestone, and gives in his De Uten-
silibus, what is perhaps the earliest reference to
the mariner's compass that we have. Albertus
Magnus, the Dominican (1193-1280), in his
treatise, De Mineralibus, enumerates different kinds
of natural magnets and states some of the prop-
erties commonly attributed to them; the min-
strel, Guyot de Provins, in a famous satirical poem,
written about 1 208, refers to the directive qual-
viii

INTRODUCTORY

ity of the lodestone and its use in navigation, as
do also Cardinal de Vitry in his Historia Orien-
talis (1215-1220); Brunetto Latini, poet, orator
and philosopher, in his Tresor des Sciences, a veri-
table library, written in Paris in 1 260 ; Ray-
mond Lully, the Enlightened Doctor, in his
treatise, De Contemplation, begun in 1272, and
Guido Guinicelli, the poet-priest of Bologna,
who died in i 276.

The authors of these learned works were too
busy with the pen to find time to devote to the
close and prolonged study of natural phenomena
necessary for fruitful discovery, and so had to con-
tent themselves with recording and discussing in
their tomes the scientific knowledge of their age
without making any notable additions to it.

But this was not the case with such contem-
poraries of theirs as Roger Bacon, the Francis-
can, and his Gallic friend, Pierre de Maricourt,
commonly called Petrus Peregrinus, the subject
of the present notice, a man of academic culture
and of a practical rather than speculative turn of
mind. Of the early years of Peregrinus nothing

THE LETTER OF PEREGRINUS

is known save that he studied probably at the Uni-
versity of Paris, and that hegraduated with the high-
est scholastic honors. He owes his surname to
the village of Maricourt, in Picardy, and the ap-
pellation Peregrinus, or Pilgrim, to his having
visited the Holy Land as a member of one of the
crusading expeditions of the time.

In 1269 we find him in the engineering corps
of the French army then besieging Lucera, in
Southern Italy, which had revolted from the auth-
ority of its French master, Charles of Anjou. To
Peregrinus was assigned the work of fortifying
the camp and laying mines as well as of con-
structing engines for projecting1 stones and fire-
balls into the beleaguered city.

It was in the midst of such warlike preoccu-
pations that the idea seems to have occurred to
him of devising a piece of mechanism to keep
the astronomical sphere of Archimedes in uni-
form rotation for a definite time. In the course
of his work over the new motor, Peregrinus was
gradually led to consider the more fascinating
problem of perpetual motion itself with the result

INTRODUCTORY

that he showed, at least diagrammatically, and to
his own evident satisfaction, how a wheel might
be driven round forever by the power of mag-
netic attraction.

Elated over his imaginary success, Peregrinus
hastened to inform a friend of his at home ; and
that his friend might the more readily compre-
hend the mechanism of the motor and the func-
tions of its parts, he proceeds to set forth in a
methodical manner all the properties of the lode-
stone, most of which he himself had discovered.
It is a fortunate circumstance that this Picard
friend of his was not a man learned in the sci-
ences, otherwise we would probably never have
had the remarkable exposition which Peregrinus
gives of the phenomena and laws of magnetism.
This letter of 3,500 words is the first great land-
mark in the domain of magnetic philosophy, the
next being Gilbert's De Magnete,\n 1600.

The letter was addressed from the trenches
at Lucera, Southern Italy, in August, i 269,10 Sige-
rus de Foucaucourt, his "amicorum intimus,"
the dearest of friends. A more enlightened friend,

THE LETTER OF PEREGRINUS

however, than the knight of Foucaucourt was
Roger Bacon, who held Peregrinus in the very
highest esteem, as the following glowing testi-
mony shows : " There are but two perfect math-
ematicians," wrote the English monk, " John of
London and Petrus de Maharne-Curia, a Picard."
Further on in his Opus Tertium, Bacon thus ap-
praises the merits of the Picard : " I know of
only one person who deserves praise for his work
in experimental philosophy, for he does not care
for the discourses of men and their wordy war-
fare, but quietly and diligently pursues the works
of wisdom. Therefore, what others grope after
blindly, as bats in the evening twilight, this man
contemplates in all their brilliancy because he is
a master of experiment. Hence, he knows all
natural science whether pertaining to medicine
and alchemy, or to matters celestial and terres-
trial. He has worked diligently in the smelting
of ores as also in the working of minerals ; he is
thoroughly acquainted with all sorts of arms and
implements used in military service and in hunt-
ing, besides which he is skilled in agriculture and

INTRODUCTORY

in the measurement of lands. It is impossible to
write a useful or correct treatise in experimental
philosophy without mentioning this man's name.
Moreover, he pursues knowledge for its own sake;
for if he wished to obtain royal favor, he could
easily find sovereigns who would honor and en-
rich him."

This last statement is worthy of the best ut-
terances of the twentieth century. Say what they
will, the most ardent pleaders of our day for or-
iginal work and laboratory methods cannot sur-
pass the Franciscan monk of the thirteenth cen-
tury in his denunciation of mere book learning
or in his advocacy of experiment and research,
while in Peregrinus, the mediaevalist, they have
Bacon's impersonation of what a student of sci-
ence ought to be. Peregrinus was a hard worker,
nor a mere theorizer, preferring, Procrustean-
like, to make theory fit the facts rather than facts
the theory; he was a brilliant discoverer who
knew at the same time how to use his discoveries
for the benefit of mankind ; he was a pioneer of
science and a leader in the progress of the world.

THE LETTER OF PEREGRINUS

An analysis of the " Epistola " shows that

(tf) Peregrinus was the first to assign a defi-
nite position to the poles of a lodestone, and to
give directions for determining which is north and
which south;

(^) He proved that unlike poles attract each
other, and that similar ones repel ;

(r) He established by experiment that every
fragment of a lodestone, however small, is a com-
plete magnet, thus anticipating one of our fun-
damental laboratory illustrations of the molecu-
lar theory ;

(d] He recognized that a pole of a magnet
may neutralize a weaker one of the same name,
and even reverse its polarity ;

(e] He was the first to pivot a magnetized
needle and surround it with a graduated circle,
Figs. 2 and 3.'

(f ] He determined the position of an object
by its magnetic bearing as done to-day in com-
pass surveying ; and

1 It is probable that Flavio Gioja, an Italian pilot, some fifty years
later, added the compass-card and attached it to the magnet.

INTRODUCTORY

(g) He introduced into his perpetual motion
machine, Fig. 4, the idea of a magnetic motor,
a clever idea, indeed, for a thirteenth century en-
gineer.

This rapid summary will serve to show that
the letter of Peregrinus is one of great interest
in physics as well as in navigation and geodesy.
For nearly three centuries, it lay unnoticed among
the libraries of Europe, but it did not escape Gil-
bert, who makes frequent mention of it in his
De Magnete, 1 600 ; nor the illustrious Jesuit writ-
ers, Cabasus, who refers to it in his Philosophia
Magnetic a, 1629, and Kircher, who quotes from
it in his De Arte Magnetica, 1641 ; it was well
known to Jean Taisnier, the Belgian plagiarist,
who transferred a great part of it verbatim to the
pages of his De Natura Magnetis, 1562, without
a word of acknowledgment. By this piece of
fraud, Taisnier acquired considerable celebrity,
a fact that goes to show the meritorious char-
acter of the work which he unscrupulously
copied.

This memorable letter is divided into two

THE LETTER OF PEREGRINUS

parts : the first contains ten chapters on the gen-
eral properties of the lodestone ; the second has
but three chapters, and shows how the author pro-
posed to use a lodestone for the purpose of pro-
ducing continuous rotation.

There are many manuscript copies of the let-
ter in European libraries : the Bodleian has six ;
the Vatican, two ; Trinity College, Dublin, one;
the Bibliotheque Nationale, Paris, one ; Leyden,
Geneva and Turin, one each. The Leyden MS.
has acquired special notoriety from a passage which
appears near the end of it in which reference is
made to magnetic declination and its value given :
but Prof. W. Wenckebach, of The Hague, has
shown' that the lines are spurious, having been in-
terpolated in the manuscript in the early part of
the sixteenth century.

The Leyden manuscript has also led some
writers to believe in a fictitious author of the let-
ter, one Peter Adsiger, or Petrus Adsigerus. As
said above, Sigerus was the name of his country-
man, to whom Peregrinus addressed his letter,

1 Annali di Matematica Pura ed Applicata, 1865.

INTRODUCTORY

the Epistola ad Sigerum, from the trenches at Luc-
era, in August, 1269.

Magnetic declination was unknown to Pere-
grinus, else he would not have written the follow-
ing words : " Wherever a man may be, he finds
the lodestone pointing to the heavens in accord-
ance with the position of the meridian " (Chapter
X). Of course, the geographical meridian is the
one here meant, as the necessity of a distinct
magnetic meridian had not yet occurred to any
one.

Nor was this important magnetic element
known to Columbus when he sailed from the
shores of the Old World in 1492 as appears from
the surprise with which he noticed the deviation
of the needle from North as well as from the
consternation of his pilots. Columbus has the
unquestionable merit of being the first to observe
and record the change of declination with change
of place.

The first printed edition of the Epislola, now
very rare, was prepared by Achilles Gasser, a phy-
sician of Lindau, a man well versed in mathe-

THE LETTER OF PEREGRINUS

matics, astronomy, history and philosophy. The
work was printed in Augsburg in 1558. A copy
of this early print is among the treasures of the
Wheeler collection in the library of the Ameri-
can Institute of Electrical Engineers, New York.
It was from this text that the translation which
follows was made.

Besides the Latin edition of Gasser, 1558,
there is also that of Libri in his Histoire des Sci-
ences Mathematiques, 1838 ; of Bertelli, 1868, and
Hellmann, 1898. Bertelli's is a learned and ex-
haustive work in which the Barnabite monk, some-
times called by mistake, Barnabita, instead of Ber-
telli, collates and compares the readings of the
two Vatican codices with other texts, adding copi-
ous references and explanatory notes. It appeared
in the Bulletino di Eibliografia e di Storia delle Science
Matematiche e Fisiche for 1868.

Of translations, we have that which Richard
Eden made from Taisnier's pirated extracts, the
first dated edition appearing in 1579. Cavallo's
Treatise on Magnetism, 1800, also contains some
of the more remarkable passages. The only com-

INTRODUCTORY

plete English translation that we have, appeared
in 1902 from the scholarly pen of Prof. Silvanus
P. Thompson, of London. It is an edition deluxe
beautifully rubricated, but limited to 250 copies.
The translation was based on the texts of Gasser
and Hellmann, amended by reference to a man-
uscript in the author's possession, dated 1391.
We are informed that Mr. Fleury P. Mottelay,
of New York, the learned translator of Gilbert's
De Magnete, possesses a manuscript version by
Prof. Peirce, of Harvard, of the Paris codex, of
which he made a careful study in an endeavor to
decipher the illegible parts.

PART I

THE LETTER OF
PEREGRINUS

PART I
CHAPTER I

PURPOSE OF THIS WORK

DEAREST OF FRIENDS:
T your earnest request, I will now make

A

known to you, in an unpolished narrative,
the undoubted though hidden virtue of the lode-
stone, concerning which philosophers up to the
present time give us no information, because it
is characteristic of good things to be hidden in
darkness until they are brought to light by ap-
plication to public utility. Out of affection for
you, I will write in a simple style about things
entirely unknown to the ordinary individual.
Nevertheless I will speak only of the manifest
properties of the lodestone, because this tract will
form part of a work on the construction of phil-
osophical instruments. The disclosing of the

THE LETTER OF PEREGRINUS

hidden properties of this stone is like the art of
the sculptor by which he brings figures and seals
into existence. Although I may call the matters
about which you inquire evident and of inesti-
mable value, they are considered by common
folk to be illusions and mere creations of the im-
agination. But the things that are hidden from
the multitude will become clear to astrologers
and students of nature, and will constitute their
delight, as they will also be of great help to those
that are old and more learned.

Y

CHAPTER II
QUALIFICATIONS OF THE EXPERIMENTER

OU must know, my dear friend, that who-

ever wishes to experiment, should be ac-
quainted with the nature of things, and should
not be ignorant of the motion of the celestial
bodies. He must also be skilful in manipulation
in order that, by means of this stone, he may pro-
duce these marvelous effects. Through his own
industry he can, to some extent, indeed, correct

THE LETTER OF PEREGRINUS

the errors that a mathematician would inevitably
make if he were lacking in dexterity. Besides,
in such occult experimentation, great skill is re-
quired, for very frequently without it the desired
result cannot be obtained, because there are many
things in the domain of reason which demand
this manual dexterity.

CHAPTER III
CHARACTERISTICS OF A GOOD LODESTONE

lodestone selected must be distinguished
by four marks — its color, homogeneity,
weight and strength. Its color should be iron-
like, pale, slightly bluish or indigo, just as pol-
ished iron becomes when exposed to the corrod-
ing atmosphere. I have never yet seen a stone
of such description which did not produce won-
derful effects. Such stones are found most fre-
quently in northern countries, as is attested by
sailors who frequent places on the northern seas,
notably in Normandy, Flanders and Picardy.
This stone should also be of homogeneous ma-

THE LETTER OF PEREGRINUS

terial ; one having reddish spots and small holes
in it should not be chosen; yet a lodestone is
hardly ever found entirely free from such blem-
ishes. On account of uniformity in its compo-
sition and the compactness of its innermost parts,
such a stone is heavy and therefore more valua-
ble. Its strength is known by its vigorous at-
traction for a large mass of iron ; further on I
will explain the nature of this attraction. If you
chance to see a stone with all these characteris-
tics, secure it if you can.

CHAPTER IV

HOW TO DISTINGUISH THE POLES OF A
LODESTONE

I WISH to inform you that this stone bears in
itself the likeness of the heavens, as I will
now clearly demonstrate. There are in the heav-
ens two points more important than all others,
because on them, as on pivots, the celestial sphere
revolves : these points are called, one the arctic
or north pole, the other the antarctic or south
pole. Similarly you must fully realize that in
6

THE LETTER OF PEREGRINUS

this stone there are two points styled respect-
ively the north pole and the south pole. If you
are very careful, you can discover these two
points in a general way. One method for doing
so is the following : With an instrument with
which crystals and other stones are rounded let
a lodestone be made into a globe and then pol-
ished. A needle or an elongated piece of iron
is then placed on top of the lodestone and a line
is drawn in the direction of the needle or iron,
thus dividing the stone into two equal parts.
The needle is next placed on another part of the
stone and a second median line drawn. If de-
sired, this operation may be performed on many
different parts, and undoubtedly all these lines
will meet in two points just as all meridian or
azimuth circles meet in the two opposite poles
of the globe. One of these is the north pole,
the other the south pole. Proof of this will be
found in a subsequent chapter of this tract.

A second method for determining these im-
portant points is this : Note the place on the
above-mentioned spherical lodestone where the
point of the needle clings most frequently and

THE LETTER OF PEREGRINUS

most strongly ; for this will be one of the poles
as discovered by the previous method. In order
to determine this point exactly, break off a small
piece of the needle or iron so as to obtain a frag-
ment about the length of two fingernails ; then
put it on the spot which was found to be the
pole by the former operation. If the fragment
stands perpendicular to the stone, then that is,
unquestionably, the pole sought ; if not, then
move the iron fragment about until it becomes
so ; mark this point carefully ; on the opposite
end another point may be found in a similar man-
ner. If all this has been done rightly, and if
the stone is homogeneous throughout and a
choice specimen, these two points will be dia-
metrically opposite, like the poles of a sphere.

CHAPTER v

HOW TO DISCOVER THE POLES OF A LODESTONE AND
HOW TO TELL WHICH IS NORTH AND WHICH SOUTH

poles of a lodestone having been located
in a general way, you will determine which
is north and which south in the following man-
8

THE LETTER OF PEREGRINUS

ner : Take a wooden vessel rounded like a plat-
ter 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.

THE LETTER OF PEREGRINUS

CHAPTER VI
HOW ONE LODESTONE ATTRACTS ANOTHER

T717HEN you have discovered the north and
the south pole in your lodestone, mark
them both carefully, so that by means of these
indentations they may be distinguished whenever
necessary. Should you wish to see how one lode-
stone attracts another, then, with two lodestones
selected and prepared as mentioned in the pre-
ceding chapter, proceed as follows : Place one
in its dish that it may float about as a sailor in
a skiff, and let its poles which have already been
determined be equidistant from the horizon, i. e.,
from the edge of the vessel. Taking the other
stone in your hand, approach its north pole to
the south pole of the lodestone floating in the
vessel ; the latter will follow the stone in your
hand as if longing to cling to it. If, conversely,
you bring the south end of the lodestone in your
hand toward the north end of the floating lode-
stone, the same phenomenon will occur ; namely,
the floating lodestone will follow the one in your
hand. Know then that this is the law : the north

10

THE LETTER OF PEREGRINUS

pole of one lodestone attracts the south pole of
another, while the south pole attracts the north.
Should you proceed otherwise and bring the north
pole of one near the north pole of another, the
one you hold in your hand will seem to put the
floating one to flight. If the south pole of one
is brought near the south pole of another, the
same will happen. This is because the north
pole of one seeks the south pole of the other,
and therefore repels the north pole. A proof of
this is that finally the north pole becomes united
with the south pole. Likewise if the south pole
is stretched out towards the south pole of the
floating lodestone, you will observe the latter to
be repelled, which does not occur, as said before,
when the north pole is extended towards the
south. Hence the silliness of certain persons is
manifest, who claim that just as scammony at-
tracts jaundice on account of a similarity between
them, so one lodestone attracts another even more
strongly than it does iron, a fact which they sup-
pose to be false although really true as shown by
experiment.

ii

THE LETTER OF PEREGRINUS

CHAPTER VII

HOW IRON TOUCHED BY A LODESTONE TURNS
TOWARDS THE POLES OF THE WORLD

IT is well known to all who have made the
experiment, that when an elongated piece
of iron has touched a lodestone and is then fas-
tened to a light block of wood or to a straw and
made float on water, one end will turn to the
star which has been called the Sailor's star be-
cause it is near the pole; the truth is, however,
that it does not point to the star but to the pole
itself. A proof of this will be furnished in a
following chapter. The other end of the iron
will point in an opposite direction. But as to
which end of the iron will turn towards the
north and which to the south, you will observe
that that part of the iron which has touched the
south pole of the lodestone will point to the north
and conversely, that part which had been in con-
tact with the north pole will turn to the south.
Though this appears marvelous to the uniniti-
ated, yet it is known with certainty to those who
have tried the experiment.

12

THE LETTER OF PEREGRINUS

CHAPTER VIII
HOW A LODESTONE ATTRACTS IRON

IF you wish the stone, according to its 'natural
desire, to attract iron, proceed as follows:
Mark the north end of the iron and towards
this end approach the south pole of the stone,
when it will be found to follow the latter. Or,
on the contrary, to the south part of the iron
present the north pole of the stone and the lat-
ter will attract it without any difficulty. Should
you, however, do the opposite, namely, if you
bring the north end of the stone towards the
north pole of the iron, you will notice the iron
turn round until its south pole unites with the
north end of the lodestone. The same thing
will occur when the south end of the lodestone
is brought near the south pole of the iron.
Should force be exerted at either pole, so that
when the south pole of the iron is made touch
the south end of the stone, then the virtue in
the iron will be easily altered in such a manner
that what was before the south end will now
become the north and conversely. The cause is

13

THE LETTER OF PEREGRINUS

that the last impression acts, confounds, or count-
eracts and alters the force of the original move-
ment.

CHAPTER IX

WHY THE NORTH POLE OF ONE LODESTONE
ATTRACTS THE SOUTH POLE OF AN-
OTHER AND VICE VERSA

\ S already stated, the north pole of one lode-
•*• ^ stone attracts the south pole of another
and conversely; in this case the virtue of the
stronger becomes active, whilst that of the weaker
becomes obedient or passive. I consider the fol-
lowing to be the cause of this phenomenon : the
active agent requires a passive subject, not merely
to be joined to it, but also to be united with it,
so that the two make but one by nature. In the
case of this wonderful lodestone this may be
shown in the following manner: Take a lode-
stone which you may call A Z), in which A is
the north pole and D the south ; cut this stone
into two parts, so that you may have two distinct

H

THE LETTER OF PEREGRINUS

stones; place the stone having the pole A so
that it may float on water and you will observe
that A turns towards the north as before; the
breaking did not destroy the properties of the
parts of the stone, since it is homogeneous;
hence it follows that the part of the stone at
the point of fracture, which may be marked B,
must be a south pole; this broken part of which
we are now speaking may be called A B. The
other, which contains Z), should then be placed
so as to float on water, when you will see D
point towards the south because it is a south
pole ; but the other end at the point of fracture,
lettered C, will be a north pole ; this stone may
now be named C D. If we consider the first
stone as the active agent, then the second, or
C Z), will be the passive subject. You will also
notice that the ends of the two stones which
before their separation were together, after
breaking will become one a north pole and the
other a south pole. If now these same broken
portions are brought near each other, one will
attract the other, so that they will again be

15

THE LETTER OF PEREGRINUS

joined at the points B and C, where the fracture
occurred. Thus, by natural instinct, one single
stone will be formed as before. This may be
demonstrated fully by cementing the parts to-
gether, when the same effects will be produced
as before the stone was broken. As you will
perceive from this experiment, the active agent
desires to become one with the passive subject
because of the similarity that exists between
them. Hence C, being a north pole, must be
brought close to B, so that the agent and its
subject may form one and the same straight line
in the order A B, C D and B and C being at
the same point. In this union the identity
of the extreme parts is retained and preserved
just as they were at first; for A is the north pole
in the entire line as it was in the divided one;
so also D is the south pole as it was in the di-
vided passive subject, but B and C have been
made effectually into one. In the same way it
happens that if A be joined to D so as to make
the two lines one, in virtue of this union due to
attraction in the order C D A B, then A and D
16

THE LETTER OF PEREGRINUS

will constitute but one point, the identity of the
extreme parts will remain unchanged just as they
were before being brought together, for C is a
north pole and B a south, as during their sepa-
ration. If you proceed in a different fashion,
this identity or similarity of parts will not be
preserved ; for you will perceive that if C, a
north pole, be joined to A, a north pole, con-
trary to the demonstrated truth, and from these
two lines a single one, B A C D, is formed, as
D was a south pole before the parts were united,
it is then necessary that the other extremity
should be a north pole, and as B is a south pole,
the identity of the parts of the former similarity
is destroyed. If you make B the south pole as
it was before they united, then D must become
north, though it was south in the original stone ;
in this way neither the identity nor similarity
of parts is preserved. It is becoming that when
the two are united into one, they should bear
the same likeness as the agent, otherwise nature
would be called upon to do what is impossible.
The same incongruity would occur if you were

I7

THE LETTER OF PEREGRINUS

to join B with D so as to make the line A B D C,
as is plain to any person who reflects a moment.
Nature, therefore, aims at being and also at act-
ing in the best manner possible ; it selects the
former motion and order rather than the second
because the identity is better preserved. From
all this it is evident why the north pole attracts
the south and conversely, and also why the south
pole does not attract the south pole and the
north pole does not attract the north.

CHAPTER x

AN INQUIRY INTO THE CAUSE OF THE NATURAL
VIRTUE OF THE LODESTONE

/CERTAIN persons who were but poor in-
^^ vestigators 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
18

THE LETTER OF PEREGRINUS

many different parts of the globe the lodestone
is found; from which it would follow that the iron
needle should turn in different directions accord-
ing to the locality ; but this is contrary to expe-
rience. Secondly, these individuals do not seem to
know that the places under the poles are unin-
habitable 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 wher-
ever 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 neces-
sary consequence of this is that the needle does

19

THE LETTER OF PEREGRINUS

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 al-
ways 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 like-
wise 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

20

THE LETTER OF PEREGRINUS

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 ex-
perimenting. If now the stone be moved ac-
cording to the motion of the heavens, you will
be delighted in having discovered such a won-
derful 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 mer-
idian, 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.

21

PART II

THE LETTER OF
PEREGRINUS

PART II

CHAPTER I

THE CONSTRUCTION OF AN INSTRUMENT FOR MEAS-
URING 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 con-
nected therewith, let us now come to those in-
struments which depend for their operation on
the knowledge of those facts. Take a rounded
lodestone,1 and after determining its poles in the
manner already mentioned, file its two sides so
that it becomes elongated at its poles and occu-
pies 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 sepa-

1 A tcrrella, or earthkin.

25

THE LETTER OF PEREGRINUS

rated 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 diam-
eter. Move the strip until it is equally distant
from the meridian-line, previously determined
and marked by a thread, or else until it coin-
cides therewith. Then mark a line on the cap-
sules 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 cardi-
nal 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 cir-
cumference of the capsules. Engrave these divi-
26

THE LETTER OF PEREGRINUS

sions on them as usually done on the back of
an astrolabe. On the top or edge of the cap-
sules 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 azi-
muth 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 in-
dicate the azimuth just as in the case of the sun.
By means of the azimuth may then be deter-
27

THE LETTER OF PEREGRINUS

mined 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.

FIG. I. — AZIMUTH COMPASS

CHAPTER II

THE CONSTRUCTION OF A BETTER INSTRUMENT
FOR THE SAME PURPOSE

TN this chapter I will describe the construc-
-•• tion of a better and more efficient instrument.
Select a vessel of wood, brass or any solid ma-
terial you like, circular in shape, moderate in
28

THE LETTER OF PEREGRINUS

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 an-
gles to each other ; through one of them pass
an iron stylus or needle, through the other a sil-
ver 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 men-
tioned 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
29

THE LETTER OF PEREGRINUS

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

TIC. 2. — DOUBLE -PIVOTED NEEDLE

FIG. 3.— PIVOTED COMPASS

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 mir-

3°

THE LETTER OF PEREGRINUS

rors. Such, then, is the description of the instru-
ment illustrated below. (See Figs. 2 and 3.)

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 remark-
able 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 in-
variably failed to notice that by means of the vir-
tue 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 mir-
ror, and worked on the outside with fine carv-
ing 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

THE LETTER OF PEREGRINUS

iron nails or teeth of equal weight fastened to
the periphery of the wheel in a slanting direc-
tion, 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 uni-
form 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 pre-
pared 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 un-
touched, 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 to-
wards 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

32

THE LETTER OF PEREGRINUS

teeth comes near the north pole and owing to
the impetus of the wheel passes it, it then ap-
proaches 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 con-

. 4.— PERPETUAL MOTION WHEEL

stantly repelled. 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

33

THE LETTER OF PEREGRINUS

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 lode-
stone. Let the places between the teeth be suit-
ably 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 Dom-
ini MCCLXIX.

34

NOTES

35

EARLY REFERENCES TO
THE MARINER'S COMPASS

THE following are the passages referred to in the intro-
ductory 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 etlam 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

37

THE LETTER OF PEREGRINUS

the pole star is concealed through the troubled state of the at-
mosphere." l

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 Wor-
cester, 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 j

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 ;

1The Chronicles and Memoirs of Great Britain and Ireland during
the Middle Ages, by Thomas Wright (1863).

38

NOTES

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 Htstoria 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 neces-
sary 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 Htstoria 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, be-
came bishop of Ratisbonne in 1260, and died in 1280. Thomas
Aquinas the greatest of schoolmen, was among his pupils.

39

THE LETTER OF PEREGRINUS

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 al-
ways be guided by a spirit of justice."

Brunette Latini, in his Tresor 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 lode-
stone directs the end of the needle to the star to which that part
itself turns."

Brunette Latini (1230-1294) was a man of great eminence
in the thirteenth century; Dante was among his pupils at Flor-
ence. For political reasons, he removed to Paris, where he
wrote his Tresor and also his Tesoretto. He visited Roger
Bacon at Oxford about 1260.

In his treatise De Contemplatione, begun in 1272, Ray-
mond 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.

40

NOTES

Ristoro d'Arezzo, in his Libra 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." '

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.

1 The pole-star was thus named in the south of France and the north
of Italy because seen beyond the mountains (the Alps).

University of California

SOUTHERN REGIONAL LIBRARY FACILITY

405 Hilgard Avenue, Los Angeles, CA 90024-1388

Return this material to the library

from which it was borrowed.

Univer

Sou

Lit