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The beginning of experimental studies of magnetism in Europe
Earth.Science Reviews/A tlas - Elsevier Publishing Company - Printed in The Netherlands
Petrus Peregrinus' EPISTO LA The Beginning of Experimental Studies of Magnetism in Eurol
PETER J. SMITH1
Seven hundred years ago, Europe produced a scientific document of unusual originality, the most important advance in the knowledge of magnetic properties to emerge from Europe since the discovery of lodestone by the Greeks. On August 8, 1269, in a manuscript which bears remarkable resemblace to a modern scientific paper, Petrus Peregrinus, a French soldier, extolled the virtue of exper'_n-nent several centuries before the betterknown propaganda of Francis Bacon (Bacon, 1620), described experiments with a lodestone sphere 331 years before William Gilbert published the results of his own in D e M a g n e t e (Gilbert, 1600) and, in designing a perpetual motion machine, began the long trail towards the unattainable. In a single short treatise Peregrinus (Peregrinus, 1269) achieved a contribution to magnetic knowledge which had eluded the classical cultures of Europe for a millenium. THE CLIMATE Although the Greek, Thales, had known of lodestone by about -600, the magnetic 'climate' in Europe around the middle of the +13th century was still extremely rarified. At the end of a whole millenium of science and philosophy ( - 6 0 0 to +400), Europeans knew that lodestone would attract pieces of iron and that the attractive power carried across some distance, but not that the strength of the attraction depended upon the degree of separation of lodestone and iron. They knew, further, that the attracted iron would adhere to the lodestone magnet, that the magnet induced attractive power in the iron and that the influence of this induced power became progressively smaller as more pieces of iron were added at greater distances from the lodestone, but not that lodestone could be used to make the iron permanently magnetic. The phenomenon of magnetic repulsion had been discovered, probably in Egypt; and magnetic power of either sign was known to act through magnetically inert substances such as brass, silver and water. However, the most significant failure was that classical Europe had been quite unable to make the conceptual leap from a knowledge of attraction and repulsion to the idea of polarity; and thus never perceived the magnet's directional property which alone could have led to the development of the magnetic compass. The reasons for the Greek failure to progress in magnetic discovery were two-fold. Firstly, magnetism was the only example of 'action at a distance' known to them (apart from electrostatic attraction which was attributed to the same cause); and even at this 1Geophysics Department, University of Liverpool, Liverpool, Great Britain
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late date it is not difficult to visualise the conceptual problems involved here. But more important, perhaps, classical culture had an inbuilt bias in favour of speculation at the expense of experiment. Although Thales and his school had sought to break away from the completely mythical tradition to formulate objective explanations for material phenomena, little tradition of experiment developed. The interaction between theory and observation which we now regard as essential for true scientific advance was almost completely lacking. Thus although the Greeks, in particular, made significant advances in attempting to replace myth, they were not, and did not pretend to be, intent upon a course of scientific exploration as we know it (Hesse, 1961). Rather, they were trying to construct a consistent, aesthetically pleasing, metaphysical system to explain what they knew of nature. The Chinese, on the other hand, had made greater but independent progress. Although there are no known references to magnetism in Chinese texts as old as that attributed to Thales, there is copious mention of the attractive power of the magnet from the - 3 r d century onwards (Needham, 1962). 'Action at a distance' held no terrors for the Chinese, who were accustomed to regarding the physical world as a continuum. Whereas the Greeks were used to thinking in terms of particles, or 'atoms', as the basic mechanism for reactions between bodies, the Chinese view held that each body possessed its own characteristic 'rhythm' (chhi) so that the ability of bodies to react depended essentially on the capacity of bodily rhythms to harmonise. The Chinese were also sophisticated experimentalists (Needham, 1962). By at least the + 1st century they had invented the compass in the form of a lodestone spoon rotating upon a smooth board. During succeeding centuries they advanced to the floating, drypivoted and fibre-suspended compasses using iron needles rather than lodestone magnets. They had discovered magnetic declination by at least the early +8th centure (Smith and Needham, 1967). Each of these discoveries and inventions appeared before the +13th century, but because of China's isolation, remained hidden from Europe. Down to the year +1190 there is not a single reference to the compass in any extant European text. Around that time Alexander Neckam (Neckam, 1190) refers briefly to a compass of fairly advanced form, though whether this was a pivoted compass or not is still a matter of controversy (Bertelli, 1868). In any event, a complete lack of antecedent European reference to the compass, combined with the omission of any reference to magnetic directivity by Neckam or his contemporaries, suggests that Neckam's compass was an import, ultimately from China, rather than indigenous to Europe. THE CIRCUMSTANCES
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'let us travel back to the year 1269 AD; King Henry III on the throne of England and Charles of Anjou but recently crowned King of the two Sicilies by Pope Urban IV; the Crusades still a living movement; Friar Roger Bacon writing crude science, or what passed for such in his time, in his retirement in Paris, Oxford having proved too orthodox for him. Over all such inquiries and speculations, whether relating to chemistry, optics, or any other occult science, the bigotry of the Middle Ages - bigotry scholastic as much as ecclesiastical - hung like a pall. The new spirit, which from two to three centuries later revived classical learning, discovered a new continent, and invented printing, was not yet born. Such was the time' (Thompson, 1906). During the early +13th century Frederick II, the Emperor of Germany, had founded the town of Lucera in southern Italy as a refuge for Saracen outcasts. But in +1266 Charles of Anjou, King of Naples and Sicily, captured it, only to find its inhabitants rebelling against his authority as soon as he had left. He thus found it necessary to beseige Lucera a second time, although not until +1269 did it finally capitulate, having held out against starvation for a whole year. Among Charles' army at the seige of Lucera was one Pierre Pderin de Maricourt
(Magister Petrus Peregrinus), probably a military engineer and evidently above the average soldier in intelligence and learning. Maricourt, the name of P61erin's native village in Picardy, has frequently been replaced by the appelation 'Peregrinus' (pilgrim), an honorary title indicating its holder to have taken part in the Crusades to the Holy Land. 'Magister' indicates that Peregrinus was an educated man who had achieved high credit as a scholar. Little else is known of him apart from the eulogy by his contemporary Roger Bacon. 'There are only two perfect mathematicians, namely, Master John of London [a student of Bacon] and Master Peter of Maricourt, a P i c a r d . . . I know of only one person who deserves praise for works of this science, for he does not trouble about discourses or quarrels over words, but follows the works of wisdom and keeps quietly to them. And so, though others strive blinkingly to see, as a bat in the twilight, the light of the sun, he himself contemplates it in its full splendour, on account of which he is a master of experiment' (Bacon, 13th century). On August 8, 1269, during the seige of Lucera, Peregrinus addressed a letter about his magnetic experiments to Sygerus de Foucaucourt, not a scholar himself but a knight who happened to be Peregrinus' close neighbour in Picardy. Although Peregrinus is reported to have written on other scientific matters, the Epistola, as his letter of +1269 has become known, is his only work to survive.
THE DOCUMENT In +1600, William Gilbert (Gilbert, 1600), who was convinced of the case for experimentation, found it necessary to make the point that 'in the discovery of secret things and in the investigation of hidden causes, stronger reasons are obtained from sure experiments and demonstrated arguments than from probable conjectures and the opinions of philosophical speculators.' Seventy-six years later Joseph Glanville (Glanville, 1676) put it even more bluntly when he wrote that one particular experiment, the construction of the magnetic compass, 'did more for the increase of knowledge and the advantage of the w o r l d . . , than the numerous subtile disputers that have rived ever since the Erection of the School of Wrangling.' By the seventeenth century, the commitment to experimentation sometimes associated particularly with the name of Francis Bacon, and which was later to serve science so well, had barely taken root. ('By the knowledge of physical causes there cannot fail to follow many indications and designations of new particulars, if men in their speculation will keep one eye upon use and practice'.) (Bacon, 1605). In this right, therefore, it is surprising to f'md the +13th century Peregrinus in no doubt at all as to the value of the experimental method. Although there are certain situations in which theoretical considerations are useful and certain subjects which are amenable to the 'realm of reason', the study of magnetism is one which requires, above all, the experimental approach. 'An investigator of this subject must have an understanding of nature and not be ignorant of the celestial motions. He must also be clever in the use of his hands in order that, by means of this stone, he may produce wonderful effects. For by his carefulness he will be able in a short time to correct an error which in an age he could never do by his knowledge of natural sciences and mathematics, if skill were lacking in the use of his hands.' In an age dominated by the classical view that speculation and mental reasoning were of greater consequence than experiment, it is of special significance to learn that 'we investigate many things by manual history, and in general without it we are unable to bring anything to completion. Whilst Alexander Neckam and his contemporaries had sought to reconcile facts with pre-existing speculation, Peregrinus aimed to use his experimental data from which to draw conclusions. In this sense the significar~ce of the Epistola transcends the new knowledge contained therein. Nevertheless, Peregrinus' advances in knowledge were important both in their own right and as a vindication of his philosophy. Perhaps the most significant single result in
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the Epistola was that Peregrinus was able to define the concept of polarity for the first time in Europe. The experiments upon which this breakthrough were based are in themselves interesting, for over 300 years before Gilbert published the results of his celebrated experiments on the spherical 'terrella', Peregrinus had trodden the same path. In fact, there is little doubt that Gilbert owed more to Peregrinus than he cared to admit. He mentions briefly that Peregrinus had used a terrella and praises the Epistola as 'a pretty erudite book considering the time'. On the other hand he makes no further reference to Peregrinus ~actual experiments and on several occasions insinuates that the Epistola is based upon second-hand knowledge. But to return to the 13th century: Peregrinus determined the positions of the poles of a lodestone sphere in three ways, each of which illustrated an important magnetic property. The first method was to place a short, fine iron needle on the surface of the sphere to define the meridian through the point of contact. Repetition of this process at different positions on the sphere produced a series of magnetic meridians all of which intersected at two points 'just as all the meridian-circles of the globe meet in the two opposite poles of the world.' By 'poles of the world' Peregrinus meant the poles of the universe rather than just the poles of the earth, since at that time terrestrial and heavenly poles were assumed to lie in the same line (Smith, 1968). Nevertheless the dipolar nature of lodestone had been discovered for the first time in Europe; and the experimentally determined singular points were christened north and south poles by analogy with the universe. Further, 'there is another better way of finding these points, namely, that you note the place on the rounded stone, as has been described, where the end of the needle or of the iron clings more frequently or with greater force. For this place will be one of the points determined by the method already described.' Nor was that all. Using an oblong needle 'about as long as two finger-nails' Peregrinus was able to show that at the poles the force acted vertically. In a series of simple experiments, Peregrinus thus discovered what 2000 years of science had failed to discover, namely (1) the dipolar nature of the magnet, (2) the fact that magnetic force is vertical at the poles (although Peregrinus was not familiar with force fields, of course), and (3) that this force is strongest at the poles. He then went on to show that like poles repel and unlike poles attract (and hence that a magnet cut in two produces two magnets); and became the first to formulate this law. Further proof, if proof be needed, of Peregrinus' commitment to experiment is provided in the conjunction of a conviction and an experimental result. Peregrinus was quick to refute the long-standing myth that the magnetic power of lodestone is derived from lodestone deposits in various parts of the world. It is rather from 'the poles of the world that the poles of the magnet receive their virtue.' On the other hand he shows experimentally not only that lodestone may be used to magnetise iron 'permanently' but that magnetism is unstable in the sense that iron magnets may be repolarised in the opposite sense. The implied dichotomy here seems not to have troubled Peregrinus. If, as he thought, the magnet received its 'virtue' from the heavenly spheres one might have expected him to be disturbed by the magnetic instability which could be interpreted as inconsistency on the part of the heavens and, by implication, God. The fact that he sticks by his experimental observations without so much as a murmur of doubt implies a degree of faith remarkable in a climate of speculation and ecclesiastical dogma. The second part of the Epistola contains descriptions of two types of magnetic compass, one floating and one pivoted. If we assume that Alexander Neckam's compass was not pivoted, Peregrinus' version becomes the first pivoted compass to have been described in Europe. In any event it was the first detailed description of the compass in Europe; and insofar as the instruments incorporated fiducial lines they were more sophisticated than Neckam's. The floating and pivoted compasses as illustrated in the Peregrinus manuscript are shown in Fig. la and 2a, respectively. Over 600 years later Bertelli (1868) reconstructed the two compasses from Peregrinus' descriptions (Figures lb and 2b) to prove their workability.
Fig. 1. (a) The floating compass described in Peregrinus' Epistola and (b) Bertelli's (1868) reconstruction. An oval magnet (rnagnes) is placed in a bowl which floats in water in a larger transparent vessel. The top of the inner vessel is graduated such that 0 ° corresponds to east (ortus), 90 ° to south (rneridies), 180 ° to west (occasus) and 270 ° to north (septentrio). These directions are with respect to the axis of the magnet each pole (polus lapidis) which Peregrinus had previously determined. A ruler with erect pins (regula cum erectis stylis) rests on the edges of the graduated bowl; and is used to determine the azimuth of the sun or moon. The ruler is turned until the shadows of the pins fall longitudinally down it. The magnetic azimuth of the sun (or moon) is then the angle between the ruler and the magnetic axis. The thin wooden strip (lignum gracile) is used to determine the fiducial line across the larger vessel. Note: The style and precise details shown by Peregrinus' illustrations vary slightly from manuscript to manuscript. Figs. la, 2a and 3 are from the first printed edition of 1558.
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Eig. 2. (a) Peregrinus' pivoted compass and (b) Bertelli's (1868) reconstruction. The iron magnet is placed through the pivot which rotates in a transparent vessel (cf. the fixed pivot of the modern compass). The ruler with erect pins serves the same purpose as in the floating compass. The vessel is g~aduated as before. Oriens = east; occidens = west. The lodestone shown here was used to magnetise the iron needle.
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These compasses were the result of the application of basic principles; and thus belong to the history of technology rather than basic science. However, one feature of the pivoted compass deserves further mention here - the brass or silver needle placed through the pivot at right angles to the magnetic needle. It was probably intended merely as an east-west indicator; but Benjamin (1895) has pointed out an interesting consequence of its presence. As the pivot rotated in the earth's field the non-magnetic, but conducting, needle would have had currents induced in it producing a damping tendency. Uninten. tionally, Peregrinus' pivoted compass would thus have been more stable than its precursors and probably even some of its successors. The third instrument to be described by Peregrinus was a perpetual motion machine, 'a continuaUy moving wheel of wonderful ingenuity', the forerunner of many hundreds of subsequent attempts to defy nature. A silver circle shaped like a bracelet was somehow supported to rotate about a vertical axis through its centre. The circle was ornamented and perforated 'both for the sake of beauty and lightening its weight'; and on the inside were fixed iron teeth rather as the teeth on a ratchet wheel (Fig. 3). An oval magnet on a
Fig. 3. Peregrinus' 'continually moving wheel o f wonderful ingenuity'. For supposed mode of operation see text. Polus meridion = south pole;polus septentrional = north pole; axis immobil = f'Lxed axis; denticuli ferrei = iron teeth; calculus = pebble.
fLxed arm within the wheel projected towards the teeth. Peregrinus' description of the operation of the system is more or less incomprehensible; but presumably he expected the magnet to attract the prominent portion of one tooth, which would then be carried by momentum beyond the magnet so that the second tooth would then be in a position to be attracted. Needless to say, the machine failed to work though apparently only 'through lack of skill rather than a defect of nature.' In view of the paucity of scientific information during the +13th century, it is surely right that this was 'an error for which we must hold the century rather himself responsible' (Peregrinus, 1269). THE ACHIEVEMENT
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Although written in +1269 and receiving wide circulation during the succeeding centuries, the Epistola was not published in printed form under Peregrinus' name until +1558. In that year Achilles Pirmin Gasser, a Lindau physician, issued it together with an introduction and postscript by himself. Recently (8arton, 1947), an earlier printed edition, published in Rome no later than +1520, has come to light; but the authorship was miscredited (deliberately?) to one Raymond Lullus. The Epistola was also the cause of
blatant plagiarism in +1562 when Jean Taisnier (Taisner) published an almost word-forword copy o f Gasser's edition without mentioning either Peregrinus or Gasser. ('May the gods damn all such sham, pilfered, distorted works', raved Gilbert (Gilbert, 1600). At this late date it is difficult to assess the influence o f Peregrinus' work. In hindsight, manuscripts of such obvious merit tend to assume a greater significance than they may have possessed. Certainly Peregrinus' faith in experiment took many centuries to catch on generally, and then probably not as a direct result of the Epistola. On the other hand, William Gilbert, whose influence on the course of magnetic discovery is undisputed, leaned heavily on Peregrinus. Irrespective of influence, the Epistola chalked up a remarkable number of European 'firsts'. Besides Gilbert's snide comments on Peregrinus' originality, some other authors (Peregrinus, 1269) have sought to detract from Peregrinus' achievement on the grounds that since other writers o f the period express similar ideas, Peregrinus was only summarising the conventional wisdom of the day. Whilst this is possible, study of the tone and style of other texts suggests otherwise. For example, the Anfidotarium Nicolai of John of St. Amand, sometimes cited in this connection (Thorndike, 1946), is a vague document lacking the incisiveness of the Epistola. It is the Epistola which possesses all the characteristics o f an original; and as such is the earliest known work o f true experimental science in Europe. REFERENCES Bacon, F., 1605. The Advancement of Learning, G.W. Kitchin (Editor), 1962. Dent, London, 246 pp. Bacon, F. 1620. Novum Organum. Ed. T.Fowler, London, 1878. Bacon, R., 13th Century. Opus Tertium. Ed. Brewer, V., London, 1859. Benjamin, P., 1895. The Intellectual Rise In Electricity. Longmans Green, London, 611 pp. Bertelli, P., 1868. Sopra Pierre Peregrine di Maricourt e la sua Epistola de Magnete. Rome. Gilbert, W. 1600. De Magnete. Dover Publications, New York, 1958. 368 pp. (English trans: Mottelay, P. F.) Glanville, J. 1676. Essay on Several Important Subjects. London. Hesse, M. B., 1961. Forces and Fields: The Concept o f Action at a Distance in the History of Physics. Nelson, London. Neckam, A., ca. 1190 De Rerum Naturis and De Utensilibus. Needham, J. 1962. Science and Civilization in China, Vol. 4, Part l. Cambridge University Press, London, 434 pp. Peregrinus, P., 1269. Epistola de Magnete. English trans: Harradon, H. D., 1943. Some early contributions to the history of geomagnetism. Terr. Mag. Atmos. Elec., 48:3-17. Sarton, G., 1947. The first edition of Petrus Peregrinus, 'De Magnete' (before 1520). Isis, 37:178. Smith, P. J., 1968. Pre-Gilbertian conceptions of terrestrial magnetism. Tectonophysics, 6:499-510. Smith, P. J. and Needham, J, 1967. Magnetic declination in mediaeval China. Nature, 214:1213-1214. Thompson, S. P., 1906. Petrus Peregrinus de Maricourt and his Epistola de Magnete. Prec. Brit. Acad., 2:377. Thorndike, L., 1946. John of St. Amand on the Magnet.. Isis, 36:156.
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the reception afterward~
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Petrus Peregrinus' EPISTO LA The Beginning of Experimental Studies of Magnetism in Eurol
PETER J. SMITH1
Seven hundred years ago, Europe produced a scientific document of unusual originality, the most important advance in the knowledge of magnetic properties to emerge from Europe since the discovery of lodestone by the Greeks. On August 8, 1269, in a manuscript which bears remarkable resemblace to a modern scientific paper, Petrus Peregrinus, a French soldier, extolled the virtue of exper'_n-nent several centuries before the betterknown propaganda of Francis Bacon (Bacon, 1620), described experiments with a lodestone sphere 331 years before William Gilbert published the results of his own in D e M a g n e t e (Gilbert, 1600) and, in designing a perpetual motion machine, began the long trail towards the unattainable. In a single short treatise Peregrinus (Peregrinus, 1269) achieved a contribution to magnetic knowledge which had eluded the classical cultures of Europe for a millenium. THE CLIMATE Although the Greek, Thales, had known of lodestone by about -600, the magnetic 'climate' in Europe around the middle of the +13th century was still extremely rarified. At the end of a whole millenium of science and philosophy ( - 6 0 0 to +400), Europeans knew that lodestone would attract pieces of iron and that the attractive power carried across some distance, but not that the strength of the attraction depended upon the degree of separation of lodestone and iron. They knew, further, that the attracted iron would adhere to the lodestone magnet, that the magnet induced attractive power in the iron and that the influence of this induced power became progressively smaller as more pieces of iron were added at greater distances from the lodestone, but not that lodestone could be used to make the iron permanently magnetic. The phenomenon of magnetic repulsion had been discovered, probably in Egypt; and magnetic power of either sign was known to act through magnetically inert substances such as brass, silver and water. However, the most significant failure was that classical Europe had been quite unable to make the conceptual leap from a knowledge of attraction and repulsion to the idea of polarity; and thus never perceived the magnet's directional property which alone could have led to the development of the magnetic compass. The reasons for the Greek failure to progress in magnetic discovery were two-fold. Firstly, magnetism was the only example of 'action at a distance' known to them (apart from electrostatic attraction which was attributed to the same cause); and even at this 1Geophysics Department, University of Liverpool, Liverpool, Great Britain
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late date it is not difficult to visualise the conceptual problems involved here. But more important, perhaps, classical culture had an inbuilt bias in favour of speculation at the expense of experiment. Although Thales and his school had sought to break away from the completely mythical tradition to formulate objective explanations for material phenomena, little tradition of experiment developed. The interaction between theory and observation which we now regard as essential for true scientific advance was almost completely lacking. Thus although the Greeks, in particular, made significant advances in attempting to replace myth, they were not, and did not pretend to be, intent upon a course of scientific exploration as we know it (Hesse, 1961). Rather, they were trying to construct a consistent, aesthetically pleasing, metaphysical system to explain what they knew of nature. The Chinese, on the other hand, had made greater but independent progress. Although there are no known references to magnetism in Chinese texts as old as that attributed to Thales, there is copious mention of the attractive power of the magnet from the - 3 r d century onwards (Needham, 1962). 'Action at a distance' held no terrors for the Chinese, who were accustomed to regarding the physical world as a continuum. Whereas the Greeks were used to thinking in terms of particles, or 'atoms', as the basic mechanism for reactions between bodies, the Chinese view held that each body possessed its own characteristic 'rhythm' (chhi) so that the ability of bodies to react depended essentially on the capacity of bodily rhythms to harmonise. The Chinese were also sophisticated experimentalists (Needham, 1962). By at least the + 1st century they had invented the compass in the form of a lodestone spoon rotating upon a smooth board. During succeeding centuries they advanced to the floating, drypivoted and fibre-suspended compasses using iron needles rather than lodestone magnets. They had discovered magnetic declination by at least the early +8th centure (Smith and Needham, 1967). Each of these discoveries and inventions appeared before the +13th century, but because of China's isolation, remained hidden from Europe. Down to the year +1190 there is not a single reference to the compass in any extant European text. Around that time Alexander Neckam (Neckam, 1190) refers briefly to a compass of fairly advanced form, though whether this was a pivoted compass or not is still a matter of controversy (Bertelli, 1868). In any event, a complete lack of antecedent European reference to the compass, combined with the omission of any reference to magnetic directivity by Neckam or his contemporaries, suggests that Neckam's compass was an import, ultimately from China, rather than indigenous to Europe. THE CIRCUMSTANCES
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'let us travel back to the year 1269 AD; King Henry III on the throne of England and Charles of Anjou but recently crowned King of the two Sicilies by Pope Urban IV; the Crusades still a living movement; Friar Roger Bacon writing crude science, or what passed for such in his time, in his retirement in Paris, Oxford having proved too orthodox for him. Over all such inquiries and speculations, whether relating to chemistry, optics, or any other occult science, the bigotry of the Middle Ages - bigotry scholastic as much as ecclesiastical - hung like a pall. The new spirit, which from two to three centuries later revived classical learning, discovered a new continent, and invented printing, was not yet born. Such was the time' (Thompson, 1906). During the early +13th century Frederick II, the Emperor of Germany, had founded the town of Lucera in southern Italy as a refuge for Saracen outcasts. But in +1266 Charles of Anjou, King of Naples and Sicily, captured it, only to find its inhabitants rebelling against his authority as soon as he had left. He thus found it necessary to beseige Lucera a second time, although not until +1269 did it finally capitulate, having held out against starvation for a whole year. Among Charles' army at the seige of Lucera was one Pierre Pderin de Maricourt
(Magister Petrus Peregrinus), probably a military engineer and evidently above the average soldier in intelligence and learning. Maricourt, the name of P61erin's native village in Picardy, has frequently been replaced by the appelation 'Peregrinus' (pilgrim), an honorary title indicating its holder to have taken part in the Crusades to the Holy Land. 'Magister' indicates that Peregrinus was an educated man who had achieved high credit as a scholar. Little else is known of him apart from the eulogy by his contemporary Roger Bacon. 'There are only two perfect mathematicians, namely, Master John of London [a student of Bacon] and Master Peter of Maricourt, a P i c a r d . . . I know of only one person who deserves praise for works of this science, for he does not trouble about discourses or quarrels over words, but follows the works of wisdom and keeps quietly to them. And so, though others strive blinkingly to see, as a bat in the twilight, the light of the sun, he himself contemplates it in its full splendour, on account of which he is a master of experiment' (Bacon, 13th century). On August 8, 1269, during the seige of Lucera, Peregrinus addressed a letter about his magnetic experiments to Sygerus de Foucaucourt, not a scholar himself but a knight who happened to be Peregrinus' close neighbour in Picardy. Although Peregrinus is reported to have written on other scientific matters, the Epistola, as his letter of +1269 has become known, is his only work to survive.
THE DOCUMENT In +1600, William Gilbert (Gilbert, 1600), who was convinced of the case for experimentation, found it necessary to make the point that 'in the discovery of secret things and in the investigation of hidden causes, stronger reasons are obtained from sure experiments and demonstrated arguments than from probable conjectures and the opinions of philosophical speculators.' Seventy-six years later Joseph Glanville (Glanville, 1676) put it even more bluntly when he wrote that one particular experiment, the construction of the magnetic compass, 'did more for the increase of knowledge and the advantage of the w o r l d . . , than the numerous subtile disputers that have rived ever since the Erection of the School of Wrangling.' By the seventeenth century, the commitment to experimentation sometimes associated particularly with the name of Francis Bacon, and which was later to serve science so well, had barely taken root. ('By the knowledge of physical causes there cannot fail to follow many indications and designations of new particulars, if men in their speculation will keep one eye upon use and practice'.) (Bacon, 1605). In this right, therefore, it is surprising to f'md the +13th century Peregrinus in no doubt at all as to the value of the experimental method. Although there are certain situations in which theoretical considerations are useful and certain subjects which are amenable to the 'realm of reason', the study of magnetism is one which requires, above all, the experimental approach. 'An investigator of this subject must have an understanding of nature and not be ignorant of the celestial motions. He must also be clever in the use of his hands in order that, by means of this stone, he may produce wonderful effects. For by his carefulness he will be able in a short time to correct an error which in an age he could never do by his knowledge of natural sciences and mathematics, if skill were lacking in the use of his hands.' In an age dominated by the classical view that speculation and mental reasoning were of greater consequence than experiment, it is of special significance to learn that 'we investigate many things by manual history, and in general without it we are unable to bring anything to completion. Whilst Alexander Neckam and his contemporaries had sought to reconcile facts with pre-existing speculation, Peregrinus aimed to use his experimental data from which to draw conclusions. In this sense the significar~ce of the Epistola transcends the new knowledge contained therein. Nevertheless, Peregrinus' advances in knowledge were important both in their own right and as a vindication of his philosophy. Perhaps the most significant single result in
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the Epistola was that Peregrinus was able to define the concept of polarity for the first time in Europe. The experiments upon which this breakthrough were based are in themselves interesting, for over 300 years before Gilbert published the results of his celebrated experiments on the spherical 'terrella', Peregrinus had trodden the same path. In fact, there is little doubt that Gilbert owed more to Peregrinus than he cared to admit. He mentions briefly that Peregrinus had used a terrella and praises the Epistola as 'a pretty erudite book considering the time'. On the other hand he makes no further reference to Peregrinus ~actual experiments and on several occasions insinuates that the Epistola is based upon second-hand knowledge. But to return to the 13th century: Peregrinus determined the positions of the poles of a lodestone sphere in three ways, each of which illustrated an important magnetic property. The first method was to place a short, fine iron needle on the surface of the sphere to define the meridian through the point of contact. Repetition of this process at different positions on the sphere produced a series of magnetic meridians all of which intersected at two points 'just as all the meridian-circles of the globe meet in the two opposite poles of the world.' By 'poles of the world' Peregrinus meant the poles of the universe rather than just the poles of the earth, since at that time terrestrial and heavenly poles were assumed to lie in the same line (Smith, 1968). Nevertheless the dipolar nature of lodestone had been discovered for the first time in Europe; and the experimentally determined singular points were christened north and south poles by analogy with the universe. Further, 'there is another better way of finding these points, namely, that you note the place on the rounded stone, as has been described, where the end of the needle or of the iron clings more frequently or with greater force. For this place will be one of the points determined by the method already described.' Nor was that all. Using an oblong needle 'about as long as two finger-nails' Peregrinus was able to show that at the poles the force acted vertically. In a series of simple experiments, Peregrinus thus discovered what 2000 years of science had failed to discover, namely (1) the dipolar nature of the magnet, (2) the fact that magnetic force is vertical at the poles (although Peregrinus was not familiar with force fields, of course), and (3) that this force is strongest at the poles. He then went on to show that like poles repel and unlike poles attract (and hence that a magnet cut in two produces two magnets); and became the first to formulate this law. Further proof, if proof be needed, of Peregrinus' commitment to experiment is provided in the conjunction of a conviction and an experimental result. Peregrinus was quick to refute the long-standing myth that the magnetic power of lodestone is derived from lodestone deposits in various parts of the world. It is rather from 'the poles of the world that the poles of the magnet receive their virtue.' On the other hand he shows experimentally not only that lodestone may be used to magnetise iron 'permanently' but that magnetism is unstable in the sense that iron magnets may be repolarised in the opposite sense. The implied dichotomy here seems not to have troubled Peregrinus. If, as he thought, the magnet received its 'virtue' from the heavenly spheres one might have expected him to be disturbed by the magnetic instability which could be interpreted as inconsistency on the part of the heavens and, by implication, God. The fact that he sticks by his experimental observations without so much as a murmur of doubt implies a degree of faith remarkable in a climate of speculation and ecclesiastical dogma. The second part of the Epistola contains descriptions of two types of magnetic compass, one floating and one pivoted. If we assume that Alexander Neckam's compass was not pivoted, Peregrinus' version becomes the first pivoted compass to have been described in Europe. In any event it was the first detailed description of the compass in Europe; and insofar as the instruments incorporated fiducial lines they were more sophisticated than Neckam's. The floating and pivoted compasses as illustrated in the Peregrinus manuscript are shown in Fig. la and 2a, respectively. Over 600 years later Bertelli (1868) reconstructed the two compasses from Peregrinus' descriptions (Figures lb and 2b) to prove their workability.
Fig. 1. (a) The floating compass described in Peregrinus' Epistola and (b) Bertelli's (1868) reconstruction. An oval magnet (rnagnes) is placed in a bowl which floats in water in a larger transparent vessel. The top of the inner vessel is graduated such that 0 ° corresponds to east (ortus), 90 ° to south (rneridies), 180 ° to west (occasus) and 270 ° to north (septentrio). These directions are with respect to the axis of the magnet each pole (polus lapidis) which Peregrinus had previously determined. A ruler with erect pins (regula cum erectis stylis) rests on the edges of the graduated bowl; and is used to determine the azimuth of the sun or moon. The ruler is turned until the shadows of the pins fall longitudinally down it. The magnetic azimuth of the sun (or moon) is then the angle between the ruler and the magnetic axis. The thin wooden strip (lignum gracile) is used to determine the fiducial line across the larger vessel. Note: The style and precise details shown by Peregrinus' illustrations vary slightly from manuscript to manuscript. Figs. la, 2a and 3 are from the first printed edition of 1558.
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Eig. 2. (a) Peregrinus' pivoted compass and (b) Bertelli's (1868) reconstruction. The iron magnet is placed through the pivot which rotates in a transparent vessel (cf. the fixed pivot of the modern compass). The ruler with erect pins serves the same purpose as in the floating compass. The vessel is g~aduated as before. Oriens = east; occidens = west. The lodestone shown here was used to magnetise the iron needle.
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These compasses were the result of the application of basic principles; and thus belong to the history of technology rather than basic science. However, one feature of the pivoted compass deserves further mention here - the brass or silver needle placed through the pivot at right angles to the magnetic needle. It was probably intended merely as an east-west indicator; but Benjamin (1895) has pointed out an interesting consequence of its presence. As the pivot rotated in the earth's field the non-magnetic, but conducting, needle would have had currents induced in it producing a damping tendency. Uninten. tionally, Peregrinus' pivoted compass would thus have been more stable than its precursors and probably even some of its successors. The third instrument to be described by Peregrinus was a perpetual motion machine, 'a continuaUy moving wheel of wonderful ingenuity', the forerunner of many hundreds of subsequent attempts to defy nature. A silver circle shaped like a bracelet was somehow supported to rotate about a vertical axis through its centre. The circle was ornamented and perforated 'both for the sake of beauty and lightening its weight'; and on the inside were fixed iron teeth rather as the teeth on a ratchet wheel (Fig. 3). An oval magnet on a
Fig. 3. Peregrinus' 'continually moving wheel o f wonderful ingenuity'. For supposed mode of operation see text. Polus meridion = south pole;polus septentrional = north pole; axis immobil = f'Lxed axis; denticuli ferrei = iron teeth; calculus = pebble.
fLxed arm within the wheel projected towards the teeth. Peregrinus' description of the operation of the system is more or less incomprehensible; but presumably he expected the magnet to attract the prominent portion of one tooth, which would then be carried by momentum beyond the magnet so that the second tooth would then be in a position to be attracted. Needless to say, the machine failed to work though apparently only 'through lack of skill rather than a defect of nature.' In view of the paucity of scientific information during the +13th century, it is surely right that this was 'an error for which we must hold the century rather himself responsible' (Peregrinus, 1269). THE ACHIEVEMENT
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Although written in +1269 and receiving wide circulation during the succeeding centuries, the Epistola was not published in printed form under Peregrinus' name until +1558. In that year Achilles Pirmin Gasser, a Lindau physician, issued it together with an introduction and postscript by himself. Recently (8arton, 1947), an earlier printed edition, published in Rome no later than +1520, has come to light; but the authorship was miscredited (deliberately?) to one Raymond Lullus. The Epistola was also the cause of
blatant plagiarism in +1562 when Jean Taisnier (Taisner) published an almost word-forword copy o f Gasser's edition without mentioning either Peregrinus or Gasser. ('May the gods damn all such sham, pilfered, distorted works', raved Gilbert (Gilbert, 1600). At this late date it is difficult to assess the influence o f Peregrinus' work. In hindsight, manuscripts of such obvious merit tend to assume a greater significance than they may have possessed. Certainly Peregrinus' faith in experiment took many centuries to catch on generally, and then probably not as a direct result of the Epistola. On the other hand, William Gilbert, whose influence on the course of magnetic discovery is undisputed, leaned heavily on Peregrinus. Irrespective of influence, the Epistola chalked up a remarkable number of European 'firsts'. Besides Gilbert's snide comments on Peregrinus' originality, some other authors (Peregrinus, 1269) have sought to detract from Peregrinus' achievement on the grounds that since other writers o f the period express similar ideas, Peregrinus was only summarising the conventional wisdom of the day. Whilst this is possible, study of the tone and style of other texts suggests otherwise. For example, the Anfidotarium Nicolai of John of St. Amand, sometimes cited in this connection (Thorndike, 1946), is a vague document lacking the incisiveness of the Epistola. It is the Epistola which possesses all the characteristics o f an original; and as such is the earliest known work o f true experimental science in Europe. REFERENCES Bacon, F., 1605. The Advancement of Learning, G.W. Kitchin (Editor), 1962. Dent, London, 246 pp. Bacon, F. 1620. Novum Organum. Ed. T.Fowler, London, 1878. Bacon, R., 13th Century. Opus Tertium. Ed. Brewer, V., London, 1859. Benjamin, P., 1895. The Intellectual Rise In Electricity. Longmans Green, London, 611 pp. Bertelli, P., 1868. Sopra Pierre Peregrine di Maricourt e la sua Epistola de Magnete. Rome. Gilbert, W. 1600. De Magnete. Dover Publications, New York, 1958. 368 pp. (English trans: Mottelay, P. F.) Glanville, J. 1676. Essay on Several Important Subjects. London. Hesse, M. B., 1961. Forces and Fields: The Concept o f Action at a Distance in the History of Physics. Nelson, London. Neckam, A., ca. 1190 De Rerum Naturis and De Utensilibus. Needham, J. 1962. Science and Civilization in China, Vol. 4, Part l. Cambridge University Press, London, 434 pp. Peregrinus, P., 1269. Epistola de Magnete. English trans: Harradon, H. D., 1943. Some early contributions to the history of geomagnetism. Terr. Mag. Atmos. Elec., 48:3-17. Sarton, G., 1947. The first edition of Petrus Peregrinus, 'De Magnete' (before 1520). Isis, 37:178. Smith, P. J., 1968. Pre-Gilbertian conceptions of terrestrial magnetism. Tectonophysics, 6:499-510. Smith, P. J. and Needham, J, 1967. Magnetic declination in mediaeval China. Nature, 214:1213-1214. Thompson, S. P., 1906. Petrus Peregrinus de Maricourt and his Epistola de Magnete. Prec. Brit. Acad., 2:377. Thorndike, L., 1946. John of St. Amand on the Magnet.. Isis, 36:156.
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the reception afterward~
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