Petrus Peregrinus de Maricourt

In his letter of 1269, Peregrinus explains how to identify the poles of the compasses. He also describes the laws of magnetic attraction and repulsion. The letters also contain a description of an experiment with a repaired magnet, as well as a number of compasses, one of which "you will be able to direct your steps to cities and islands and to any place whatever in the world." Indeed, the increasing perfection of magnetic compasses during the thirteenth century allowed navigators such as Vandino and Ugolino Vivaldi to strike out on voyages to unknown lands. ; The Epistola de magnete is divided into two parts. Part One (10 chapters): This is a section that serves as a model of inductive reasoning based on definite experiences, and setting forth the fundamental laws of magnetism. He did not discover these laws, but presented them in logical order. Part One discusses the physical (but not the occult) properties of the lodestone and provides the first extant written account of the polarity of magnets. He was thus the first to use the word "pole" in this context. He provides methods for determining the north and south poles of a magnet, and he describes the effects magnets have upon one another, showing that like poles repel each other and unlike poles attract each other. He also treats the attraction of iron by lodestones, the magnetization of iron by lodestones, and the ability to reverse the polarity in such an induced magnet. Peregrinus attributed the Earth's magnetism to the action of celestial poles, rather than to the terrestrial poles of the planet itself. Part Two (three chapters): This section describes three devices that utilize the properties of magnets. He treats the practical applications of magnets, describing the "wet" floating compass as an instrument, and a "dry" pivoted compass in some detail. He also attempts to prove that with the help of magnets it is possible to realize perpetual motion (see History of perpetual motion machines). His device is a toothed wheel which passes near a lodestone so that the teeth are alternately attracted by one pole and repelled by the other. ==The universal astrolabe text==

The Nova Compositio Astrolabii Particularis (found in only 4 manuscripts) describes the construction and use of a universal astrolabe which could be used at a variety of latitudes without changing the plates. Unlike al-Zarqālī's more famous universal astrolabe in which vertical halves the heavens were projected onto a plane through the poles, this one had both the northern and southern hemispheres projected onto a plane through the equator (which was also the limit of projection). There are no known surviving astrolabes based on this treatise. The use of such an astrolabe is very complicated, and since it is probable that most sophisticated users were not frequent travelers, they were more likely happier with the traditional (and simpler) stereographic planispheric astrolabe. ==Roger Bacon==

The literature often mentions that Peregrinus was praised by Roger Bacon, who called him a "perfect mathematician" and one who valued experience over argument. But the association of the praise with Peregrinus appears only in a marginal gloss to Bacon's Opus tertium and only in one of the five manuscripts used in the critical edition, which leads us to conclude that it was a later comment added by someone else. That Bacon's praise was for Peregrinus is open to serious debate. ==Legacy==

The influence of Peregrinus's astrolabe was virtually nil. His reputation derives mainly from his work on magnetism. The De magnete became a very popular work from the Middle Ages onwards, as witnessed by the large number of manuscript copies. The first printed edition of it was issued at Augsburg, in 1558, by Achilles Gasser. In 1562, Jean Taisner published from the press of Johann Birkmann of Cologne a work entitled Opusculum perpetua memoria dignissimum, de natura magnetis et ejus effectibus, Item de motu continuo. This is considered a piece of plagiarism, as Taisnier presents, as though his own, the Epistola de magnete of Peregrinus and a treatise on the fall of bodies by Gianbattista Benedetti. William Gilbert acknowledged his debt to Peregrinus and incorporated this thirteenth-century scientist's experiments on magnetism into his own treatise, called De magnete. The Epistola de magnete was later issued by Guillaume Libri (Histoire des sciences mathématiques en Italie, vol 2 [Paris, 1838], pp. 487–505), but, based on only one manuscript, this edition was full of defects; corrected editions were published by Timoteo Bertelli (in Bulletino di bibliografia e di storia delle scienze matematiche e fisiche pubblicata da B. Boncampagni, 1 (1868), 70–80) and G. Hellmann (Rara magnetica 1269-1599 [Neudrucke von Schriften und Karten über Meteorologie und Erdmagnetismus, 10], [Berlin, 1898]) . The modern critical edition was prepared by Loris Sturlese and appears in Petrus Peregrinus de Maricourt, Opera (Pisa, 1995), pp. 63–89. A translation into English has been made by Silvanus P. Thompson ("Epistle of Peter Peregrinus of Maricourt, to Sygerus of Foucaucourt, Soldier, concerning the Magnet", [London: Chiswick Press, 1902]); by Brother Arnold [=Joseph Charles Mertens] ("The Letter of Petrus Peregrinus on the Magnet, A.D. 1269", with introductory note by Brother Potamian [= M. F. O'Reilly], [New York, 1904]); and H. D. Harradon, ("Some Early Contributions to the History of Geomagnetism - I," in Terrestrial Magnetism and Atmospheric Electricity [now Journal of Geophysical Research] 48 [1943], 3–17 [text pp. 6–17]). The modern critical edition of the astrolabe text was prepared by Ron B. Thomson and appears in Petrus Peregrinus de Maricourt, Opera (Pisa, 1995), pp. 119–196. The philosopher and scientist Charles S. Peirce made a thorough study the Epistle of Petrus Peregrinus on the lodestone (MS. No. 7378; See Eisele, C. (1957) The Charles S. Peirce-Simon Newcomb Correspondence. Proceedings of the American Philosophical Society, Vol. 101, No. 5. p. 411). The European Geosciences Union (EGU) established the Petrus Peregrinus Medal in recognition for outstanding scientific contributions in the field of magnetism. ==See also==