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Astronomical Images : The meaning of terms concerning the superior planets, Venus and Mercury in astronomical tables

Gregor Reisch

Astronomical Images

<p style='text-align: justify;'>The <i>Margarita philosophica</i> was a compendium, or 'Epitome' of university learning in the sixteenth century. It was written by the prior of the house of Carthusians at Freiburg, Gregor Reisch (d. 1525), and was first published in 1503 in Freiburg by Johannes Schott, a printer from Strasbourg. The work was illustrated amply with somewhat crude woodcuts, and was divided into twelve books, with one book each dealing with the trivium (grammar, dialectic and rhetoric) and quadrivium (arithmetic, music, geometry, astronomy), four books devoted to natural philosophy, and one book on moral philosophy. It was a popular work, reprinted numerous times during the sixteenth century, including the unauthorized, augmented editions by another printer at Strasbourg, Johann Grueninger. Oronce Fine edited and added to the Latin text of the 1535 edition. In book 7, the <i>Margarita</i> includes a summary of Peuerbach's <i>Theoricae novae planetarum</i> and reproduces some of its original diagrams. It describes the spheres of Saturn, Jupiter, Mars, the Sun, Venus, Mercury, and the Moon, giving figures of their orbs, axes and poles for Saturn, the Sun, Venus, Mercury, and the Moon. Then it adds an illustrated account of the theory of eclipses, and concludes with three chapters that have no equivalent in Peuerbach's treatise: they concern the terms used in the astronomical tables (<i>De terminis tabularibus</i>) for the Sun, the Moon, and 'the other planets' (<i>De terminis tabularibus in reliquis planetis</i>). Each chapter contains a series of definitions and is illustrated by a diagram that can be used as a visual glossary. This one, presented as useful for understanding the tables concerning all the planets except the Sun and the Moon, is loosely based on the diagram that represents the lines and motions of the superior planets in Peuerbach's original (c. 1474) edition. The diagram represents a system of three orbs, similar to those of the superior planets and of Venus, but not of Mercury (which has five orbs). The outermost circle represents the zodiac (the beginning of Aries is marked). The vertical line is the line of the apogee (<i>linea augis</i>) that passes through the apogee of the eccentric deferent of the planet (<i>aux</i>), the three aligned centres of the equant circle (<i>c. equantis</i>), the eccentric deferent (<i>c. deferentis</i>), and the eighth sphere (<i>c. mundi</i>), and the perigee of the deferent (<i>oppositum augis</i>). The line that crosses it at right angles at the centre of the eighth sphere indicates the points of the eccentric deferent that are at middle distance from the Earth (between the apogee and perigee). These points are marked <i>longitudo media</i>. On these mean longitudes, see Reinhold's 1553 commentary, fols. 46r, 54r, 56r, 57v. The eccentric deferent (<i>deferens</i>) intersects with the eccentric equant (<i>equans</i>). The terms concerning the epicycle are also marked on the diagram and defined in the text. The mean apogee of the epicycle (<i>aux epicycli media</i>), point a on the diagram, is 'the point of the epicycle marked by the line drawn from the centre of the equant and passing through the centre of the epicycle' (<i>punctum epicycli per lineam a centro aequantis, per centrum epicycle ducta designatum</i>), while its true apogee (<i>aux epicycli vera</i>), point b on the diagram, is 'shown by the line drawn from the centre of the World and passing through the centre of the epicycle' (<i>per lineam a centro mundi per centrum epicycli ductam</i>). The line of the mean motion of the epicycle (<i>linea medii motus epicycli</i>) is 'the line drawn from the centre of the World to the zodiac parallel to the line from the centre of the equant passing through the centre of the epicycle' (<i>linea quae a centro mundi ad zodiacum protrahitur, linea a centro aequantis per centrum epicycli ducta aeque distans</i>). The line of the true motion of the epicycle (<i>linea veri motus epicycli</i>) is 'the line drawn from the centre of the World to the zodiac, passing through the centre of the epicycle' (<i>linea quae a centro mundi per centrum epicycli ad zodiacum ducitur</i>). Other lines determine the movement of the planet on the zodiac. The line of the true place or true motion of the planet (<i>linea veri loci, sive veri motus planetae</i>) is 'drawn from the centre of the World and passes through the body of the planet' (<i>a centro mundi per centrum corporis planetae ducitur</i>). There is a lacuna in the text that omits the definition of the line of mean motion of the planet (<i>linea medii motus</i>), but the diagram obviously shows that it is the line drawn from the centre of the World to the zodiac, parallel to the line drawn from the centre of the equant to the centre of the epicycle. Then the arcs of circles that measure the different movement of the planet are shown and explained. The mean and true motions or longitudes of the planet (<i>medius motus, verus motus</i>) are the arcs of the zodiac measured eastward from the beginning of Aries to the lines of the mean and the true motions. The mean centre of the planet (<i>centrum medium planetae</i>) is the arc of the zodiac measured eastward from the line of the apogee (<i>linea augis</i>) to the line of mean motion (<i>linea medii motus</i>). The true centre (<i>centrum verum aut aequatum planetae</i>) is measured from the line of the apogee to the line of true motion (<i>linea veri motus</i>). The equation of the centre (<i>aequatio centri</i>) is the arc of the zodiac between the lines of the mean and true motions. The equation of the epicycle (<i>aequatio epicycli</i> or <i>aequatio in epicyclo</i>) is the arc measured on the epicycle between the mean apogee and the true apogee of the epicycle. On the diagram, it is arc e, between point a and point b. The mean argument of the planet (<i>argumentum planetae medium</i>) is the arc of the epicycle measured according to the direction of the movement of this epicycle, from the mean apogee of the epicycle to the centre of the body of the planet (<i>arcus epicycli ab auge eius media, secundum motum eius ad centrum corporis planetae numeratus</i>). On the diagram it is arc ad, d representing the centre of the body of the planet. The true argument of the planet (<i>argumentum verum</i>) is also measured on the epicycle in the same direction, from the true apogee of the epicycle to the centre of the body of the planet. On the diagram, it is arc bd. The equation of the argument (<i>aequatio argumenti</i>) is the arc of the zodiac between the line of true place or motion of the planet (<i>linea veri loci planetae</i>) and the line of the true place or motion of the epicycle (<i>linea veri loci epicycli</i>); these two lines are described above. The proportional minutes (<i>minuta proportionalia</i>) are the last in the list. They are represented by the graduation marked along the line of the apogee in the inferior part of the eccentric orb (between the perigee and the exterior limit of the interior deformed orb). In this case, the text is elliptical: 'the difference between the length of the line from the centre of the World to the apogee and that from the centre of the World to the perigee, divided into sixty, gives the closer (or inner) proportional minutes; similarly, the difference between the length of the aforementioned line from the centre of the World to the apogee and that from the centre of the World to the mean longitude [divided into sixty], gives the remoter (or outer) proportional minutes' (<i>excessus quo linea a centro mundi in augem longior est lineae a centro mundi in oppositum augis, divisus in 60 partes minuta proportionalia dat propiora: sic excessus dictae lineae a centro mundi in augem, super lineam a centro mundi in longitudinem mediam, dat minuta proportionalia longiora</i>). For a more complete clarification, see Apian (1537), fol. 17r. Translated quotations of Peuerbach's <i>Theoricae</i> are from Aiton (1987). Quotations from <i>Margarita philosophica</i> are translated by Isabelle Pantin.</p>


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