Petrus Peregrinus de Maricourt

French writer and inventor

• Born: Early thirteenth century
• Birthplace: Unknown
• Died: Thirteenth century
• Place of death: Unknown

Petrus was the author of the first Western scientific treatise on the principles of magnetism. His practical inventions included a floating compass and a pivoted compass, both of which were used for finding the meridian and the azimuths of heavenly bodies.

Early Life

Very little is known about the life of Petrus Peregrinus de Maricourt (PEE-truhs pehr-eh-GRI-nuhs deh MAHR-ih-coort), a name that means Peter the Pilgrim of Maricourt. What is known comes from two sources: Peregrinus’s Epistola Petri Peregrini de Maricourt ad Sygerum de Foucaucourt, militem, de magnete (Epistle of Petrus Peregrinus de Maricourt, to Sygerus of Foucaucourt, Soldier, Concerning the Magnet, 1902), completed on August 8, 1269, at Lucera, and references in Roger Bacon’s treatise Opus tertium (c. 1266; English translation, 1912).

The surname “de Maricourt” indicates that Peregrinus hailed from Méhaircourt, a village in Picardy (an old province in northern France); whether he was born at Méhaircourt or simply lived there is not known. Given his extensive education, it is clear that he was of noble birth. The appellation “Peregrinus” has been a matter of controversy. As “Peregrinus” was an honorary title given to people who had made pilgrimages to the Holy Sepulcher in Jerusalem or who had participated in a crusade, it was formerly conjectured that Peregrinus was a Knight Templar or was a member of one of Louis IX’s Crusades in the thirteenth century. It is now recognized that “Peregrinus” was also bestowed on anyone who fought in an officially sanctioned Crusade outside the Holy Land. Thus, Peregrinus probably received his appellation from his service at the siege of Lucera, where he apparently wrote his work on magnetism.

Frederick II, the Holy Roman Emperor of Germany who was excommunicated three times in his life by the Papacy, had established early in the thirteenth century the town of Lucera in southern Italy as a colony and place of refuge for Saracens. Three times between 1255 and 1269, this town, guarded by Saracens and supported by the German emperor, was attacked by the forces of Charles I of Anjou, king of Italy. As the Papacy had declared these assaults official Crusades, Peregrinus received his title “Peregrinus” from his activity in Charles’s final siege of the city in 1268-1269. Given his keen interest in mechanical devices, it seems likely that Peregrinus served as an engineer: Perhaps he constructed machines for breaching walls or hurling objects.

Other information on Peregrinus’s life comes from Roger Bacon. In Bacon’s Opus tertium (chapter 11), Peregrinus is referred to as one of the two “perfect mathematicians” and a magister, that is, someone who had earned a master of arts degree, perhaps at the University of Paris. In chapter 13, Bacon describes Peregrinus as the greatest experimental scientist of his time and one completely skilled in alchemy, warfare, agriculture, and the theory and use of all technical arts.

Life’s Work

Although Peregrinus had planned to write a treatise on mirrors and may in fact have composed one on the composition of an astrolabe (a manuscript on such a topic bears his name in the title), his fame rests on the work on magnetism. The work is divided into two parts, theoretical and practical. The first, consisting of ten chapters, is devoted to the properties and effects of magnets and the principles of magnetism; the second discusses the construction of three instruments utilizing magnets (two compasses and a perpetual motion machine).

After an introductory chapter stating the purpose of his work, Peregrinus sets forth the qualifications of the scientist. Peregrinus insists that theory and speculation alone are insufficient; one must be good at manual experimentation, for only then can errors, undetected by abstract thinking and mathematics, be corrected. Chapter 3 contains a discussion of the properties of a good lodestone (natural magnet). It should look ironlike, slightly bluish, and pale. It should be heavy, homogeneous in material, and possessing “virtue,” or the power to attract the greatest amount of iron. Thus, in the latter instance, Peregrinus considered the extent of magnetic strength (perhaps the lifting power of the stone) to be of crucial importance.

Chapter 4 is critical to the history of magnetism, for here is the earliest account of magnetic polarity and the methods for fixing the north and south poles. The poles of the lodestone are analogous to the celestial poles. In this respect, Peregrinus followed medieval thinking. According to the cosmology of the Middle Ages, Earth was the center of the universe, fixed and immobile; around it lay ten heavens, all of which, except the outermost, where God resided, rotated about their common center. The rotation of the heavens was on an axis, the ends of which formed the north and south celestial poles. Peregrinus believed that the celestial poles attracted the magnet; it was only later that scientists, beginning with William Gilbert in 1600, thought of Earth as having its own magnetic poles.

The theory of the celestial poles led Peregrinus to form two methods of distinguishing the poles of a lodestone. The first method involves a lodestone that has been polished into a spherical shape. A needle or piece of iron is placed on the stone’s surface; a line is then drawn in the direction of the needle, dividing the sphere in half. If this procedure is performed repeatedly, all the lines (meridians) will converge at two points the poles. This conclusion represents an astounding piece of scientific experimentation: The poles of a spherical magnet are recognized and the magnetic meridians located.

The second method was also revolutionary. Peregrinus insisted that the poles can also be detected without drawing meridians simply by noting the greatest attraction of a needle by the magnetic force. Peregrinus suggested that a needle of iron, 5 or 7.5 centimeters long (about 2 or 3 inches), if moved around a lodestone, would locate the polar point, the place where the needle stands the most erect. What Peregrinus observed is the action of the magnetic field of force: At the poles the needles stand erect, and at other points, they are more or less inclined.

The next step was to determine which pole is north and which is south (chapter 5). Here Peregrinus set forth the fundamental law of magnetic polarity. If the magnet is placed in a wooden cup and the cup into a large vessel of water, then the north pole of the lodestone will point toward the north celestial pole and the south pole of the lodestone to the celestial south pole. Even if one forcibly turns the magnet away in a new direction, it will return to its true alignment. Next, the effect of one lodestone on another was demonstrated. The north pole of a lodestone, when brought close to the south pole of a second lodestone, will cause the latter to try to adhere to it; the same will happen if the south pole of the one is moved to the other’s north pole. If the reverse is done, however that is, if like poles are brought into close proximity then the poles “flee” each other. Thus Peregrinus established the law of attraction and repulsion. Peregrinus then made a further startling discovery: If a magnet is broken into two, each part will act like a magnet and have its own north and south poles; moreover, the opposite poles of the magnets will unite if brought together, thus making again a unified magnet. Peregrinus’s work was the first theory of persistence of polarity in the separate parts of a magnet.

Peregrinus next showed the action of a magnet on iron: A needle when touched by the north pole of the magnet will turn to the south celestial pole and vice versa. Thus, the south pole of the needle will be attracted to the north pole of the magnet and repelled by the south pole; the north pole of the needle will be attracted to the south pole of the magnet and repelled by the north pole. Polarity, however, can be reversed by touching the north pole of the needle with the north pole of the magnet, causing the needle’s north pole to be converted into a south pole. This observation of reversal of magnetic polarity was centuries ahead of its time.

Peregrinus finished part 1 of his work with a discussion of the cause of the virtue (attractive power) of the lodestone. He rejected the then commonly held view that mines of magnetic stone in the northern region of the world caused a magnet to be oriented on a north-south line. Instead, the poles of a magnet are influenced by the celestial poles.

Peregrinus also refuted the idea that the Pole Star was at the true north; rather, it was Polaris that rotated around that point. It should be noted, however, that Peregrinus was not aware of declination, that is, the fact that the compass needle does not point due north but at a small angle that varies from place to place. This effect had long been observed by the Chinese and is mentioned in an eleventh century work by Shen Gua (Shen Kua). The discovery in Europe of the declination was formerly attributed to Christopher Columbus during his voyage of 1492 or even to Sebastian Cabot during his voyage to Labrador in 1497-1498; current scholars, however, recognize that European mariners knew of declination long before this. The chapter closes with a description of a perpetual motion machine with pivoted spherical magnets. The magnet, made with fixed pivots at its poles so that it could freely rotate, would follow the motion of the celestial poles and so rotate. This theory was possible, one must remember, because Peregrinus believed that Earth was motionless and the celestial heavens rotated around it.

Part 2 is very important for the history of the compass. The Chinese had known about the magnet’s properties of pointing north-south and had employed it for geomancy; yet they did not apply this knowledge to the construction of a mariner’s compass until the twelfth century. At about the same time, references to the mariner’s compass appeared in Western literature; whether the compass was introduced from the East by Arab or European sailors or was independently developed is not known. This early compass was a water compass. A needle or piece of iron, after being placed on a magnetic stone, was floated on wood in a vessel of water; it would turn until it pointed in the direction of north. Hardly a sophisticated piece of equipment, this early compass gave only a directional heading and did not permit any bearings.

Peregrinus made tremendous improvements on this water compass by constructing two compasses a dry compass and a wet one. The latter consisted of an oval magnet inside a bowl or wooden case and floated on water inside a large vessel. The rim of the vessel was marked into four quadrants by the four cardinal points of the compass. Each quadrant was subdivided into ninety equal parts, or degrees. On top of the container that had the magnet inside it, Peregrinus placed a light bar of wood, with an upright pin at each end. This device allowed the navigator to determine not only the direction of the ship but also the azimuth of any heavenly body (sun, moon, or star). The innovation, in other words, was a combination of a compass needle and nautical astrolabe that was capable of steering a vessel on any given course.

Peregrinus proceeded to invent a pivoted compass. In place of the floating bowl and the vessel of water, a circular compass container was constructed with a transparent lid of glass or quartz. The top of the container was divided into the same ninety parts per quadrant as in the floating compass; then, a movable pivot rule with upright pins at each end was fastened on top of the lid. An axis of brass or silver was then fastened below the lid and the bottom of the vessel. Two needles one of iron, the other of brass or silver were inserted at right angles through the axis. The iron needle was then magnetized by a lodestone so that it would point north and south. The lid of the vessel was then turned until its north-south points were in line with those of the needle. Azimuthal readings could then be made by rotating the pivot rule to the heavenly body sought. Others later improved this compass by adding the compass card, that is, the thirty-two points of the compass affixed to the compass’s pointing needle.

Peregrinus closes his treatise with yet another attempt at perpetual motion by magnetic power. He conceived of a wheel of silver with a series of iron teeth. A magnet was to be placed at the end of a radial arm within the ring and close to the teeth. Peregrinus believed that any one tooth of the wheel would be attracted to the north pole of the magnet. Because of its attraction to the north pole, the tooth would gain enough momentum to move onto the magnet’s south pole. Here it would be repelled by the south pole, whose momentum would force that tooth beyond the magnet. The next tooth is attracted to the north pole of the magnet, and so on. This alternating attraction and repulsion of the teeth would cause the wheel, to which the teeth are attached, to move in perpetual motion.

In summary, Peregrinus found and differentiated the poles of a magnet. He then formulated the laws of magnetic repulsion and attraction and discussed the strength of the magnetic force field by the amount of inclination of an iron needle when brought into close contact with a magnet at various points. He knew that the Pole Star was not at the true north and, therefore, did not affect the magnet. He knew also about reversal of magnetic polarity. Peregrinus applied this knowledge to practical inventions.

Significance

Peregrinus’s pivoted and floating compasses allowed the determination of the meridian and the azimuths of heavenly bodies and were the first to have the fiducial line and a division of 360 degrees. He suggested the conversion of magnetic energy into mechanical energy by a perpetual motion machine.

Peregrinus’s “letter” on magnetism is the first scientific work on the subject. His work exerted considerable influence on later writers and was drawn on extensively by William Gilbert, who laid the foundation of magnetic science in 1600 in his De magnete, magneticisque corporibus, et de magnete tellure (1600; On the Magnet, Magnetic Bodies Also, and on the Great Magnet the Earth, 1860).

Bibliography

Aczel, Amir D. The Riddle of the Compass: The Invention That Changed the World. New York: Harcourt, 2001. A brief but detailed and thorough account of the invention of the compass. Also discusses the history of navigation up to the fifteenth century.

Benjamin, Park. History of Electricity. 1898. Reprint. New York: Arno Press, 1975. One of the most extensive discussions in English of Peregrinus’s life and work. The style is a bit trying, but this work explains very well the ideas expressed in Peregrinus’s treatise. Includes bibliography and index.

Gilbert, William. On the Magnet. New York: Basic Books, 1958. A reprinted edition of Gilbert’s foundational text on magnetic science.

Grant, Edward. “Petrus Peregrinus.” In Dictionary of Scientific Biography, edited by Charles C. Gillispie. Vol. 10. New York: Scribner, 1974. A definitive treatment of Peregrinus. Contains an invaluable bibliography.

Harradon, H. D. “Some Early Contributions to the History of Geomagnetism-I.” Journal of Terrestrial Magnetism and Atmospheric Electricity 48 (1943): 3-17. Contains a brief discussion of Peregrinus’s life and work, followed by a translation of the letter. (This journal is now named the Journal of Geophysical Research.)

Mottelay, Paul Fleury. Bibliographical History of Electricity and Magnetism, Chronologically Arranged. 1922. Reprint. New York: Arno Press, 1955. Contains a summation of the letter, with a bibliography on Peregrinus and the manuscripts and editions of the letter.

Peregrinus of Maricourt, Petrus. Epistle of Petrus Peregrinus of Maricourt, to Sygerus of Foucaucourt, Soldier, Concerning the Magnet. Translated by Silvanus P. Thompson. London: Chiswick Press, 1902. The translator includes a good introduction to Peregrinus’s life and theories on magnetism.

Sarton, George. From Rabbi Ben Ezra to Roger Bacon. Vol. 2 in Introduction to the History of Science. Huntington, N.Y.: R. E. Krieger, 1975. Short but very helpful biography of Peregrinus, and a summation of the contents of the letter.

Stern, David P. “Demystifying Magnetism.” The World and I 15, no. 10 (October, 2000). A brief, readable article on William Gilbert’s magnetic science, a science that was greatly influenced by Peregrinus.

Thompson, Silvanus P. “Petrus Peregrinus de Maricourt and His Epistola de magnete.” Proceedings of the British Academy 2 (1905-1906): 377-408. Extensive discussion of Peregrinus’s life, his work, and his impact.