# The actors

An annotated, working index of persons mentioned explicitly in the Defensio.

Abraham Avenezre (also Avenare) or Abraham ibn Ezra (ca. 1090-1164): An astrologer, numerologist, Hebrew grammarian and exegete, and translator from Arabic into Hebrew, Avenezre was traveled widely and diseminated Arabic learning to scholars in Italy, England and France. According to the 1512 inventory of his library, Regiomontanus owned a codex containing astrological texts by this author (Vienna, ÖNB lat. 5335). DSB. Smithius, 2006.

Ahmad ibn Yusuf (fl. 900-5): A mathematician in Egypt who wrote a commentary on Ptolemy’s Centiloquium and treatises on similar arcs, the astrolabe, and ratio and proportion. The latter text, a commentary on Euclid’s Elements, Book V, was translated into Latin by Gerard of Cremona and circulated widely in medieval Europe. The 1512 and 1522 inventories of Regiomontanus’s library indicate that he had owned a copy of Ahmad’s De proportione et proportionalitate; this codex, however, has not been found. DSB.

Albategnius or al-Battani (ca. 858-929): An Arab astronomer who composed an important zij (a work on astronomy with tables, for the epoch for 911) that treats not only the Ptolemaic theories of solar, lunar and planetary motions but also practical issues such as the construction of sundials, armillary spheres, a mural quadrant and other instruments. Although generally accepting Ptolemy’s theoretical models, Albategnius did correct their parameters by use of more recent observational data. A Latin translation of the zij was made in the twelfth century. Regiomontanus’s manuscript copy of this translation (Nuremberg, Cent. VI, 21) served as the text for Johannes Schöner’s editio princeps, Rudimenta astronomica Alfragrani ... item Albategnius (Nuremberg: Petreius, 1537). In 1899-1907, C.A. Nallino published a modern critical edition of the Arabic and Latin versions of the zij. DSB.

Albertus Magnus (ca. 1200-80): Master of theology at the University of Paris and subsequently bishop of Regensburg, Albert played a central role in rediscovering Aristotle in the Latin West and in bringing the Greek and Arabic sciences into the medieval universities. He wrote widely on the sciences ranging from zoology and embryology to mechanics and mathematics, as well as on philosophy and theology. The modern critical edition of his works, still in progress, will encompass more than 40 volumes. DSB.

Alexander the Great or Alexander III of Macedon (356-23 BCE): Creator of one of the largest empires in antiquity, Alexander became known as a legendary hero for his tactical military skills, his conquests, and his taking Greek culture to the East. He was also remembered for being tutored, as a youth, by Aristotle.

Alfraganus or Al-Farghani (d. after 861): An astronomer at the Abbasid court of al-Mamun in Baghdad, Alfraganus wrote several treatises on astronomical instruments and a non-technical summary of Ptolemy’s Almagest that was translated into Latin and Hebrew and circulated widely in medieval Europe. Around 1460 Regiomontanus made his own copy of Alfraganus’s text (Nuremberg, Cent. VI, 12). Printed editions of John of Seville’s Latin translation appeared in 1493, 1537 and 1546. Johannes Schöner prepared the 1537 edition, printed in Nuremberg by Petreius, but apparently did not use Regiomontanus’s manuscript for his edition. In 1464, Regiomontanus lectured on Alfraganus in Padua; his opening lecture was published in Schöner’s 1537 edition. DSB.

Alfonso X (1221-84): King of Castile, although eventually deposed by the Castilian nobility for having wasted too many resources trying to become Holy Roman Emperor, Alfonso was actively interested in science and patronized translation of many Arabic astronomical and astrological texts into Latin and Castilian. The eponymous Alfonsine Tables, prepared around 1472 at his court, combined earlier Arabic tables, based with some modifications on Ptolemaic theoretical models, and enabled their users with a minimum of computation to predict the all celestial motions. Originally produced in Castilian, a Latin version composed around 1321 in Paris would become the standard set of astronomical tables used across Europe until well into the sixteenth century. The editio princeps of the Alfonsine Tables was published in 1483 in Venice by Erhard Ratdolt. DSB.

Alhazen or Ibn al-Haytham (965-ca. 1040): Born in Basra, Alhazen apparently spent most of his life in Fatimid Cairo where he wrote original, comprehensive studies on optics, vision and mathematics. He also composed at least twenty texts on astronomy, including On the Configuration of the World, which criticized Ptolemy’s Almagest for not showing how physical bodies, moving according to the principles of Aristotle’s natural philosophy, could produce the observed phenomena of the heavens. Regiomontanus apparently owned copies of Alhazen’s massive work on Optics (editio princeps in 1572 in Basel) and a shorter text, Liber de crepusculis, on dawn and twilight, now no longer attributed to Alhazen. Both works appear in the 1522 inventory of Regiomontanus’s library, but neither codex has been found. DSB.

Alpetragius or Al-Bitruji (fl. ca. 1190): The leading astronomer in Islamic Spain, Alpetragius’s only known work fundamentally criticizes Ptolemaic astronomy for its violation of Aristotelian physics. Rejecting the epicycles and eccentrics of Ptolemy’s planetary models, Alpetragius developed a model of homocentric spheres, one for each planet, with rotating pivots on small circles pulling ninety-degree arc “arms” on their surfaces to account for the observed irregularities of planetary motions. Although the quantitative predictions from these models do not match the heavens as well as do the Ptolemaic models, they do qualitatively correspond to the basic celestial motions. In 1217, Michael Scot translated the work as De motibus celorum circularibus. Regiomontanus owned a copy of this translation (Nuremberg, Cent. V, 53) as well as an anonymous text critical of Alpetragius (Vienna, ÖNB lat. 5203). Another Latin version was published in Venice in 1531. Modern editions of the Arabic and Latin texts have been published by Bernard R. Goldstein and Francis J. Carmody, respectively. DSB.

Significantly, Regiomontanus throughout his career displayed a keen interest in homocentric astronomy. In 1460, he even proposed homocentric models for the Sun and Moon that differ from Alpetragius’s and promised to write a larger work outlining a fully homocentric system. Such a work, however, has not been found. See Shank 1992 and 1998; Swerdlow 1999.

Al-Zarqali (d. 1100): Known as a maker of water clocks and astronomical instruments in Toledo, al-Zarqali compiled an important set of astronomical tables that would become known as the Toledan Tables. Although the original Arabic version is lost, two Latin translations were widely used in Europe until displaced by the Alfonsine Tables early in the fourteenth century. Al-Zarqali also wrote treatises on stereographic projection and astronomical instruments and on the theory of trepidation or the slow backwards movement of the sphere of fixed stars with respect to the ecliptic or the annual path of the Sun through the sky. The first (and only) printed edition of the Toledan Tables appeared in the 2002. DSB.

Apollonius (d. early 2d century BCE): One of the leading mathematicians of Greek antiquity, Apollonius is best known for his Conics, a study of three curves now known as the parabola, hyperbola and ellipse. According to Ptolemy, Apollonius also proved that an epicyclic model is geometrically equivalent to an eccentric model, the two models that Ptolemy would develop in the Almagest into a complete astronomical system. While still a student in Vienna, Regiomontanus copied excerpts from Latin translations of many classical texts in geometry and mathematics, including from Apollonius’s Conics (Vienna, ÖNB lat. 5203). He also owned a copy on parchment of the Greek Conics (Nuremberg, Cent. V, App. 6). DSB.

Archimedes (ca. 2878 – 212 BCE): Usually considered the leading mathematician of Greek antiquity, Archimedes wrote a series of fundamentally important treatises on areas and volumes of figures bounded by curved lines and surfaces. He also wrote works applying geometry to statical and hydrostatical problems. Medieval scholars created and studied Arabic and Latin translations of most of the Archimedian corpus. During his years in Italy, Regiomontanus copied and corrected Latin translations of several Archimedes treatises (Nuremberg, Cent. V, 15). His autograph later served as the basis for the Latin translation of the editio princeps, published together with the Greek text in Basel in 1544. DSB.

Aristarchus of Samos (ca. 310-230 BCE): Born on the island of Samos and known to his contemporaries as ‘the mathematician’, Aristarchus formulated an early method for determining the relative sizes of the Sun and Moon. According to Archimedes and other ancient authorities, Aristarchus also proposed a heliocentric theory of the cosmos, with the central Sun and the fixed stars considered stationary and the Earth and planets moving around the Sun. Into his copy of Archimedes’s report of this theory, Regiomontanus wrote “Aristarchus samius” in the margin (Nuremberg, Cent. V, 15), suggesting that he knew of the ancient heliocentric theory. DSB.

Aristotle (384-22 BCE): A long-time student at Plato’s Academy in Athens, Aristotle would become the leading natural philosopher of classical antiquity. His works on method, physics, cosmology, rhetoric, and natural history were revived by Arabic scholars in the tenth century, by Greek scholars in eleventh-century Constantinople, and by Latin scholars in the twelfth century. Many of Aristotle’s works provided the curriculum for the new universities founded in the thirteenth century; writing commentaries and questions on Aristotle would remain a major preoccupation of university masters into the seventeenth century. Regiomontanus apparently owned copies of sections of Aristotle’s works on physics, respiration, and the parts of animals (in Latin), bound with his autograph copy of several astrological texts in Greek (Erlangen, University Library 1227). DSB.

Aristyllus (fl. ca. 270 BCE): Briefly mentioned by Plutarch and Ptolemy as an astronomer who observed the positions of the fixed stars. Otherwise nothing is known about him. DSB.

Bianchini, Giovanni or Iohannes Blanchinus (d. after 1469): Bianchini spent most of his life in Ferrara, working for the d’Este family, teaching at the university, and writing on mathematics and astronomy. His best-known work was a set of astronomical tables with canons or instructions for their use. The editio princeps of the tables appeared in 1495 in Venice; later editions appeared in 1526 and 1533. In a recent study of these tables, Chábas and Goldstein (2009) have shown that Bianchini used the parameters of the Alfonsine Tables but completely reworked the presentation of the tables, using double argument tables and building the computations around the mean anomalies, which made the tables bulky and complex. Around 1460 in Vienna Regiomontanus copied Bianchini’s tables (Nuremberg, Cent. V, 57) and composed his own set of canons for them. In 1463-64, the two men exchanged a series of letters, posing a series of mathematical and astronomical puzzles to each other. However, no evidence suggests that Regiomontanus and Bianchini ever met.

Boethius (ca. 480-525): Working in Rome, this encyclopedist made wide swatches of Greek learning available in simplified form for Latin readers. He apparently wrote didactic works on the quadrivium (a term he invented for the mathematical sciences of arithmetic, music, geometry and astronomy), although only his Arithmetic and Music are known. He also wrote commentaries on works of logic by Aristotle and Porphyry. Copies on parchment of the Arithmetic and Music are listed in the inventories of Regiomontanus’s library, but the codex is no longer extant. DSB.

Campanus of Novara (d. 1296): Frequently decalled “Magister,” Campanus may have been a professor at one of the early universities; however extant records do not link him to any particular university. He wrote a widely circulated commentary on Euclid’s Elements (printed fourteen times starting in 1482), texts on computus, on the sphere, and on astronomical instruments. He is best known, however, for his Theorica planetarum, the earliest technical account of Ptolemaic astronomy to be available in the Latin West. Ostensibly, the work describes an equatorium, an instrument constructed of wood that provides scale models of Ptolemy’s theory for each planet and thereby allowed users to find Ptolemaic predictions of planetary positions without using astronomical tables. The work also provides a general overview of the Almagest. Campanus’s Theorica was never printed; a modern edition was produced by F.S. Benjamin and G.J. Toomer in 1971. Regiomontanus acquired a copy of the Theorica in Vienna (Nuremberg, Cent. V, 58). DSB.

Cicero (106-43 BCE): A legendary orator and prose stylist, also a statesmen and lawyer, Cicero introduced Greek philosophy to Roman audiences. Of his voluminous works, six on rhetoric, eight on philosophy, and 58 speeches survive.

Democritus (fl. late 5^{th} century BCE): An early Greek philosopher who sought to explain
the universe in terms of atoms and voids. DSB.

Erastosthenes (ca. 276-195 BCE): A Greek scholar who spent most of his life in Alexandria, writing works on geography, mathematics, philosophy, chronology, literary criticism and grammar. His measurements of the Earth’s circumference and the obliquity of the ecliptic were widely quoted by later authors. DSB.

Euclid (fl. ca. 295 BCE): Perhaps the most famous mathematician of all time, whose Elements “exercised an influence upon the human mind greater than that of any other work except the Bible.” This fundamental work in plane geometry defined standards of mathematical proof and rigor that have characterized the field ever since. Regiomontanus owned a copy of the Elements, correcting and improving the Campanus translation through Book III, 8 (Nuremberg, Cent. VI, 13. DSB (quote at iv:415).

Eudoxus of Cnidus (ca. 400-347 BCE): A Greek scholar who invented some of the mathematical methods later axiomatized by Euclid. In his work, On Speeds, Eudoxus applied spherical geometry to astronomy, showing how combinations of nested spheres, rotating on different axes, could reproduce some of the irregularities in observed planetary motions. Later Aristotle would generalize Eudoxian spheres into a physical system for the entire cosmos. DSB.

Geber or
Jabir ibn Alfah al-Ishbili (fl. first half of 12^{th} century): Active in Seville, Geber
reworked Ptolemy’s Almagest by using a different set of theorems for spherical trigonometry. This
work, Islah al-majisti (Correction of the Almagest), also criticized Ptolemy’s order for the
planets, placing Venus and Mercury above (rather than below) the Sun. Like Theon, Geber had drawn considerable criticism in George of
Trebizond’s commentary on the Almagest. Regiomontanus’s autograph copies of the Islah and the Almagest, both in translations by Gerard of Cremona,
were bound into a single codex around 1460 in Vienna (Nuremberg, Cent. III, 25). According to historian Richard Lorch, Regiomontanus’s
On triangles, Book 4, borrows extensively from Geber without attribution, something noted by
contemporaries. Peter Apian edited and published Geber’s text (Nuremberg: Petreius, 1534). DSB.

Gersonides or Levi ben Gerson or Leo Judeaus (1288-1344): A Jew living in Orange and Avignon, Levi probably wrote only in Hebrew. He produced commentaries on the Bible and the Talmud, as well as works in mathematics, philosophy and astronomy. His best-known work, Milhamot Adonai (Wars of the Lord), written in the 1320s, describes a new observational instrument, the Jacob’s staff, and after criticizing both Ptolemy and al-Bitruji presents a novel cosmology composed of 48 spheres, mostly but not all of which are concentric with the Earth. His highly original lunar model dispenses with epicycles and eliminates the variations of lunar distance that had plagued Ptolemy’s lunar theory. The complete Milhamot has not been published; a modern, abridged edition has been prepared by B.R. Goldstein. Regiomontanus owned a copy of a Gerson text on astronomical instruments, according to the 1512 and 1522 inventories of his library. DSB.

Hipparchus (d. after 127 BCE): Although a major astronomer in Greek antiquity, only one of Hipparchus’s texts survives. Most of what we know about him comes from Ptolemy’s Almagest and its reports of Hipparchus’s observations of equinoxes and stellar positions. Ptolemy apparently adopted his solar theory from Hipparchus and attributes to him the discovery of precession, the slow motion of the equinox points through the fixed stars from east to west. Hipparchus also wrote works on geography and the sizes and distances of the Sun and Moon and on eclipses. In his text on the torquetum (a pedagogical instrument for demonstrating the basics of spherical astronomy), published by Johannes Schönner in 1544, Regiomontanus attributed an observational instrument, mentioned by Ptolemy, to Hipparchus. DSB. Schmeidler, ed., 575.

Jacobus Cremonensis (fl. 1450s): Working at the court of Pope Nicholas V, Jacobus, a Canon Regular of the Order of St. Augustine, translated several important Greek texts into Latin, including the works of Archimedes which became the standard version. Around 1462, Regiomontanus prepared his own copy of Jacobus’s translation, making corrections by comparing the translation against a Greek original from the library of Cardinal Bessarion (Nuremberg, Cent. V, 15). Regiomontanus’s manuscript later served as the basis for the editio princeps (Basel: Thomas Venatorius, 1544). In 1452 Nicholas V also asked Jacobus to evaluate George of Trebizond’s commentary on the Almagest, which ignited the public controversy about the latter work.

Jacopo Antonio Marcello (d. ca. 1464): A Venetian nobleman, senator and patron of artists and humanists. At the death of his son in 1461, Jacopo arranged for a series of consolatory letters and elegies to be composed by leading literati, including George of Trebizond. Around the same time, George dedicated to Jacopo his translation and commentary on the Almagest and his Comparatio philosophorum Aristotelis et Platonis, three of the most controversial works George produced. Clearly, George in the early 1460s was seeking Jacopo’s patronage. Monfasani, 1984; King, 1994.

János Vitéz (1408-72): Bishop of Vrad and archbishop of Esztergom, Vitéz had tutored the future King Matthias Corvinus of Hungary and served as a leading official in the King’s government until 1471 when he led a plot against the ruler and was banned. Vitéz enthusiastically supported humanist scholarship in Hungary, collected a large personal library including many astrological and astronomical books, and probably was responsible for Regiomontanus spending time in Hungary between 1467 and 1471. Peuerbach dedicated his Tabulae eclipsium to Vitéz and computed them for the meridian of Vrad. In 1460, Regiomontanus wrote a letter to Vitéz, in which he outlined non-Ptolemaic, homocentric models for the motions of the Sun and Moon and promised a larger work in which would develop a homocentric model of the cosmos, a promise Regiomontanus apparently never fulfilled. In the late 1460s, Regiomontanus dedicated his treatise on the torquetum and his Tabula directionum to Vitéz.

Joannes de Sacrobosco or John of Holywood (d. 1256): Called various names and identified as one of various nationalities, this shadowy figure seems to have been a canon regular in the Order of St. Augustine at the monastry of Holywood in Nithsdale before becoming a professor of mathematics at the university of Paris. He wrote elementary textbooks on spherical astronomy and mathematics that, into the seventeenth century, would be widely used and commented on in the curriculum of European universities. While in Italy Regiomontanus acquired copies of Sacrobosco’s texts on the sphere, on computus, and on arithmetic (Nuremberg, Cent. V, 94). DSB.

Joannes de Campo S. Petri or Giovanni da Camposampiero (fl. 1430s): A monk and lecturer on astronomy and astrology at the University of Padua. Shank 2008.

Joannes Hispalensis or John of Seville (fl. 12^{th} century): Probably the well-known
translator of Arabic astronomical and astrological texts, whose translations of Abu-Masar, Messahala, Alfragani, and Alchabitius
circulated widely in medieval Europe. Historians, however, have identified several different translators working under this or similar
names in twelfth-century Spain. See Thorndike 1959 and Burnett 1994.

Jordanus de Nemore (fl. ca. 1230: Although almost nothing is known about Jordanus’s life, he composed twelve treatises and is considered to be one of the most important mathematicians and mechanicians of the Latin Middle Ages. His Elementa Jordani super demonstrationem ponderum introduced into statics the ideas of component forces, positional gravity and the infinitesimal. His work on algebra, De numeris datis, applied analysis to algebraic problems. Consisting of more than 400 propositions, his Arithmetica was widely discussed in the Middle Ages. His Demonstratio Jordani de algorismo showed a deep knowledge of the Arabic number system and arithmetic operations. And his Liber Philotegni de triangulis is one of the most sophisticated geometries written in Latin medieval Europe. Not surprisingly, given his interests, Regiomontanus copied out sections of various works by Jordanus (Vienna, ÖNB lat. 5203) and according to inventories of 1512 and 1522 owned a copy of Jordanus’s text on the planisphere. DSB.

Julius Caesar (100-44 BCE): The Roman politician and military leader who helped transform the Roman Republic into the Roman Empire.

Leucippus (fl. 5^{th} century BCE): Known as the first Greek atomist, although no texts
have been firmly attributed to him, Leucippus’s views were later elaborated by Democritus. Leucippus is also thought to have authored
a cosmography, according to which the stars and Earth arose from a swirl of colliding bodies separated from the infinite. DSB.

Martianus Capella (365-440): Perhaps a teacher of rhetoric, Martianus is known for his textbook, De nuptiis philologiae et Mercurii, which introduced the seven liberal arts to students of the trivium and quadrivium throughout the early Middle Ages. Book VIII on astronomy provided a comprehensive and systematic account of that topic, and has been called the “best extant ancient Latin treatise on astronomy.” DSB (ix:141). Eastwood, 2007.

Matthias Corvinus (1443-90): King of Hungary, King of Bohemia and Duke of Austria, Matthias used diplomacy and mercenary troops to extend the borders of Hungary to their great extent ever and to become the most powerful ruler of central Europe in the fifteenth century. Educated by the Polish humanist, Gregory of Sanok, and the bishop of Nagyvárad, János Vitéz, Matthias knew Italian and was eager to bring Mediterranean cultural influences to Hungary. In 1465, he founded a new university in Pressburg and established a massive personal library of secular books, including many scientific works, that in size was second only to the Vatican Library in all of Europe. Regiomontanus dedicated his Tabula primi mobilis to the Hungarian king, who had a handsome copy of this text illuminated by the Florentine artist Francesco d’Antonio del Cherico (Vienna, ÖNB lat. 2363). Matthias also acquired a copy of Peuerbach’s and Regiomontanus’s Epitome (Vienna, ÖNB lat. 44) and of Regiomontanus’s Tabulae directionum for his library (Wolfenbüttel, Herzog August Bibliothek, 69.9 Aug. fol.). Presumably Regiomontanus completed this latter work after 1467, during his time in Hungary; the two men may well have met.

Menelaus of Alexandria (fl. 100): Regarded as the founder of spherical trigonometry, Menelaus wrote a book on spherical triangles, presented as propositions just as Euclid had treated plane triangles. Menelaus’s theorem for solving spherical triangles provided the foundation for Ptolemy’s treatment of spherical trignometry in the Almagest. According to inventories from 1512 and 1522, Regiomontanus owned a treatise by Menelaus on the sphere, the editio princeps of which appeared in 1558 DSB.

Nicholas V, Pope (1397-1455): Before being elected pope in 1447, Nicholas had studied theology at Bologna and had traveled through Germany, France and England, collecting books. As a youth, he had tutored members of the Strozzi and Albizzi families in Florence, where he had met many humanist writers. As pope, Nicholas enlarged the Vatican Library and patronized artists, humanists and translators of Greek texts such as George of Trebizond.

Plato (427-348 BCE): Founder of the Academy in Athens, Plato emphasized the mathematical sciences and their value in the training of philosophers. His philosophy of Forms, eternal, unchanging abstractions which the human mind at times can comprehend, would influence Western epistemology for nearly two millenia. His account of the physical world and its origin, presented in the Timaeus, helped make ideas of the divine craftsman, a spherical cosmos, and geometrical atoms central to Western cosmology. DSB.

Pliny the Elder (23-79): Pliny pioneered the development of an encyclopedic approach to nature. His hugely influential work on Natural History does not offer philosophical theories or explanations but rather breaks nature down into discrete, decontextualized entities--plants, animals, minerals, medicines, stars and planets—presented as lists of facts. He portrayed his account as comprehensive, stating in its preface that he would describe twenty thousand (i.e., an incomprehensibly large number) facts. Pliny’s discussion of astronomy, including the order of the planets out from the central Earth, served as a crucial source for early medieval authors before the twelfth-century translation of the Almagest into Latin. The work remained popular, however; at least seventeen incunabula editions of the Natural History were printed, beginning with Johannes de Spira’s (Venice, 1469). DSB; Eastwood, 2007.

Proclus (410-85): Having studied and taught at the Academy in Athens, Proclus became a leading late Neoplatonist philosopher. Less original thinker than expositor and systematizer, Proclus produced commentaries on Plato’s Timaeus and on Euclid’s Elements, an outline of Ptolemaic astronomy, an elementary treatise on spherical astronomy and many other texts on religious and philosophical issues. During his years in Italy, Regiomontanus acquired a copy of Proclus’s work on Ptolemy (Erlangen, University Library 1227); he may also have owned Proclus on the sphere. DSB. Zinner 1968, 360.

Ptolemy (c. 100-70): Undoubtedly the most creative and systematic astronomy of classical antiquity, Ptolemy in the Almagest presented geometrical and logical methods to extract parameters from carefully selected observations and to combine the geometric models of eccentrics and epicycles, developed by his predecessors, into quantitative, predictive astronomical theory. His Handy Tables reduced this theory to simple algorithms that yield planetary positions for given dates. His Planetary Hypothesis embedded the planetary models into a single comprehensive cosmos and offered a means to compute the absolute distances of the planets from the Earth. His Tetrabiblos, intended as a complement to the Almagest, is a handbook of astrology, summarizing the theory of celestial influence in terrestrial affairs. Ptolemy also composed long influential works on Optics and Geography. Regiomontanus made his own autograph copy of George of Trebizond’s Latin translation of the Almagest (Nuremberg, Cent. V, 62). He also owned owned Gerard of Cremona’s Latin translation of this text (Nuremerg, Cent. III, 25), Greek and Latin copies of the Tetrabiblos (Nuremberg, Cent. V, App. 8; Cent. V, 85; and Cent. VI, 22), and a Latin copy of the Geography (Nuremberg, Cent. V, 55). DSB.

Simplicius (ca. 500-33): A well-known Neoplatonist who wrote commentaries on Aristotle in which he tried to reconcile the thought of Plato and Aristotle. His commentary on Aristotle’s De Caelo was translated into Latin in the thirteenth century and circulated widely thereafter. Regiomontanus owned an excerpt, in Latin, of Simplicius’s commentary on Aristotle’s physics (Erlangen, University Library 1277). DSB.

Sixtus IV, Pope (1414-84): Best known for sponsoring the Sistine Chapel, Sixtus assumed the papacy in 1471. Having studied philosophy and theology at the University of Pavia, he enlarged the Vatican Library and, according to Hartmann Schedel’s Nuremberg Chronicle of 1492, called Regiomontanus to Rome in 1475 to help reform the Julian calendar. The Gregorian reform of the Julian calendar, however, would not be initiated until a century later.

Thabit ibn Qurra (836-901): An important Arabic mathematician and astronomer in Baghdad who became one of the first critics and reformers of Ptolemaic astronomy. He wrote commentaries on Euclid, texts on conic sections, spherical trigonometry and algebra. He also wrote on medical topics and mechanics. His Book on the Solar Year seeks to revise Ptolemy’s astronomy by replacing the tropic year with the sidereal year for the theory of the Sun. His On the Motion of the Eighth Sphere presents geometrical model for trepidation which introduces a periodic term into the phenomenon of precession and the obliquity of the ecliptic. Both works are technically sophisticated and demonstrate a deep understanding of Ptolemaic astronomy; recently, however, historians have questioned the attribution of the latter text to Thabit. Regiomontanus’s teacher, Peuerbach, had favorably presented “Thabit’s” theory of trepidation at the end of his Theoricae novae planetarum, written by 1454, editio princeps by Regiomontanus in 1472. In Vienna, Regiomontanus wrote a clean, autograph copy of On the Motion (Nuremberg, Cent. VI, 12) and well as of Thabit’s text on weights and the balance (Vienna, ÖNB lat. 5203). In his printing prospectus of ca. 1472, Regiomontanus announced a title, De motu octavae spherae contra Tebith suosque sectatores, that never appeared in print. DSB. Neugebauer, 1962; Goldstein 1964; Ragep, 1996.

Thales (ca. 625 – 547 BCE): Considered by Aristotle to have “founded” Ionian natural philosophy, Thales was praised for having predicted a solar eclipse and for proposing a cosmology asserting that the Earth floats on water or that water is the material substrate of all substances in the cosmos. DSB.

Theodosius of Bithynia (fl. second half of 2d century, BCE): Little is known of this Greek author except that he composed several works on the geometry of the sphere and its application to astronomical problems. The 1512 and 1522 inventories of Regiomontanus’s library list a “Teodosius de speris” but this codex has not been found. In his correspondence with Giovanni Bianchini on various geometrical problems, Regiomontanus mentioned Theodosius. In his printing prospectus of ca. 1472, he listed a “new translation” of three works by Theodosius, including the Spherica; none of these works appeared. The Latin translation of the Spherica was first printed in 1518; the editio princeps of the Greek text appeared in 1558. DSB.

Theon of Alexandria (fl. 360): Probably a teacher of astronomy and mathematics at the “Museum” in Alexandria, Theon is best known for his exegetical and rather uncritical commentaries on Ptolemy’s Almagest and Handy Tables. He also produced an edition of Euclid’s Elements that circulated widely, a treatise on the astrolabe, now lost, and probably invented the idea of trepidation of the tropical points with respect to the fixed stars. Apparently, George of Tebizond took a very critical attitude toward Theon’s commentary on the Almagest, which prompted Regiomontanus to defend the latter work. From Cardinal Bessarion, Regiomontanus received Greek copies of Theon’s commentaries on the Almagest and the Handy Tables (Nuremberg, Cent. V, App. 8). Inventories of his library suggest that he also had a Latin translation (codex not found). Regiomontanus’s printing prospectus of ca. 1472 lists Theon’s commentaria in Almaiestum; however, the editio princeps of the Greek commentary appeared in 1538, probably based on Regiomontanus’s manuscript. DSB.

Timocharis (fl. 300 BCE): The earliest Greek astronomer known to have recorded significant numbers of observations of lunar, planetary and stellar positions. But none of his writings are extant; his observations are known only from Ptolemy’s reports. DSB.

Witelo (ca. 1230-75): Probably born in Silesia, Witelo had studied at the universities of Paris and Padua and in the 1270s composed a massive work on optics, Perspectiva, for which he drew heavily from Ibn al-Haytham’s Optics. Rather than considering the nature of light (its ontology), Witelo emphasized the geometrical analysis of light’s propogation as rays. The 1512 and 1522 inventories of Regiomontanus’s library list Witelo’s Perspectiva, but this codex has not been found. The title also appears on Regiomontanus’s printing prospectus of ca. 1472; but the editio princeps was printed in 1535 by Petreius in Nuremberg. DSB.