Astronomical Images : Definition of lines and angles
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 the 1512 edition, Grueninger attached an appendix consisting of material not discussed extensively in the original Schott edition. This appendix included Greek and Hebrew alphabets, musical notation, perspective and architecture, and explanation of such instruments as the quadrant, astrolabe, and torquetum. Figures in the right-hand margin show encircling, and circular lines (<i>linea circumferens</i>, <i>circularis</i>): a flexible or tortuous line (<i>linea flexosa vel tortuosa</i>), obtuse, acute and right angles (<i>angulus obtusus</i>, <i>acutus</i>, <i>rectus</i>), right and obtuse angles of a sphere (<i>angulus sphaeralis rectus</i>, <i>obtusus</i>), angle touching a sphere (<i>angulus contingentiae sphaerae</i>), superficial angle (<i>angulus superficialis</i>), complementary angles (<i>anguli coalteri</i>), straight surface (<i>superficies recta</i>), curved surface (<i>superficies curva</i>). The left-hand margin lists figures for a semi-circular line (<i>linea semicircularis</i>), an angle made between lines (<i>angulus</i>), an angle between planes (<i>angulus planis</i>), a solid angle (<i>angulus solidus</i>), and an angle made with two straight lines drawn from the centre to the circumference of a circle, marked k. In the 1503 edition, the mark for this angle in a circle was *, which could have been confused with a mark for a star. This may be the reason why the angle is marked k in this edition.</p>
