A sharp criticism of George of Trebizond’s commentary on the Almagest (C.1.19), this massive work survives mainly in the St Petersburg MS, which was Regiomontanus’s working copy, with numerous corrections and additions, all in his hand. The work cannot be dated precisely, but it is likely that Regiomontanus began writing it as early as 1462 and that he kept working on and revising it until his death in 1476. The Escorial MS, which contains an incomplete copy of Books I-III, is also Regiomontanus’s autograph.
Text ‘(St Petersburg, BAN, IV-1-935, ed. Shank/Kremer) (37r-39r) [preface] Nuper quosdam offendi commentarios in magnam Claudii Ptolemaei compositionem inclito ac Christianissimo Pannoniarum regi Matthiae autore Georgio Trapezuntio inscriptos, quorum ingenti magnitudine subitaque novitate mirum in modum letabar, talis iamdiu cupieris expectans muneris, multo autem maximum videndi desiderium ardorem instinxit maiestas principis cui opus illud dedicatum erat. Non enim nisi elegantissimo quolibet atque optimo — ab iniuriis distat abstinere siquando alieno indire peccata sua recognoverit. [title] Defensio Theonis contra Trapezuntium. (2r-17r) [book i] In prefatione Leonem Judeum carpens inquit: Nec potuit percipere dispositiones aeris propinquitatem et remotionem in visu plurimum immutare. Propinquiora enim apparent que humido crassoque medio cernimus — Sed tale aliquid dicit de Ptolemeo Geber in tractatu suo septimo ubi centrum ecentrici alicuius trium superiorum investigatur. (17v-29v) [book ii] Secundus liber. In capitulo Quinto secundi libri: Meridianus, inquit, et orizon quoniam maximi circuli in duo equalia — ubi enim locus dabitur, multo plura pronunciabit lingua. (29v-36v and 40v-50r) [book iii] In capitulo tertio libri tertii premittit quasdam vocabulorum diffinitiones ubi prorumpit — sed inversas ac falsas hominis temerarii exposiunculas pessundare. (50v-57v) [book iv] Secundus: Super quarto libro quas homo iste temerarius ineptias effutire ausit circa inspectiones lunares — quod reliquum est alibi abundius manifestabitur. (57v-92r) [book v] Iam quantum Ptolemei librum ab iniquis exposiunculis vidicare iubemur — reciprocam sibi quandam prestarent investigandi facultatem. (92r-144r) [book vi] Percusis hactenus deliramentis quibus argutissima Ptolemei doctrina ab expositore — de stellis fixis atque erraticis perperam commentus es, cur sim excribare pergemus. (144r-147v) [book vii] Cum equidem primum ad defendendum viros inique lacessitos animum appuli — quicquid super his duobus scripsit voluminibus in unum quasi acervum confersit. (147v-150v) [book viii] Octavus autem quoniam narrationis fili (?) sensum derelicto — Verum cum huiuscemodi leviores a plerique omnibus peccata satis emendare possint. (151r-186v) [book ix] Noni deinceps voluminis commenta per lustrare aggrediemur ubi in primis — ceteris tradiderit planetis expeditiorem cursum habentibus aliquis animadvertat. (186v-190r) [book x] De Venere quidem circa principium decimi voluminis pauca cum dixerit — centro equantis producte ad centrum epicycli sui reperiatur. (190r-207r) [book xi] Item in calce capituli primi libri undecimi de stella Iovis eandem autor — passionibus de doctrina hominis periculum faciemus. (207r-244r) [book xii] Quartus. Super duodecimo incipe. Superius igitur etsi hominis peritia astronomia explorata sit — nefando fumo obtenebrare non erubescit. (244r-302v) [book xiii] Donec de hoc hominis monstro iudicatis ad postrema nos deinceps — clientulo indicatam tuo declinare velis. Hinc procul fugite quicumque sideralem queritis disciplinam commentariosque mendaces una cum autore suo Georgio Trapezuntio sinite valere.
Bibl. E. Zinner, Regiomontanus: His Life and Work, Amsterdam-New York-Oxford-Tokyo, 1990 (tr. with additions of Leben und Wirken des Joh. Müller von Königsberg, genannt Regiomontanus, Osnabrück, 1968), 97-98; M. Shank, ‘Regiomontanus and Homocentric Astronomy’, Journal for the History of Astronomy 29 (1998), 157-166: 161-163; M. Shank, ‘Regiomontanus on Ptolemy, Physical Orbs, and Astronomical Fictionalism: Goldsteinian Themes in the “Defense of Theon against George of Trebizond”’, Perspectives on Science 10 (2002), 179-207; M. Shank, ‘Regiomontanus as a Physical Astronomer: Samplings from The Defence of Theon against George of Trebizond’, Journal for the History of Astronomy 38 (2007), 325-349; M. Malpangotto, Regiomontano e il rinnovamento del sapere matematico e astronomico nel Quattrocento, Bari, 2008, 45-48; H. Zepeda, The Medieval Latin Transmission of the Menelaus Theorem, PhD dissertation, University of Oklahoma at Norman, 2013, 339; M. Shank, ‘Regiomontanus and Astronomical Controversy in the Background of Copernicus’ in Before Copernicus. The Culture and Contexts of Scientific Learning in the Fifteenth Century, eds R. Feldhay, F. J. Ragep, Montreal-London-Chicago, 2017, 79-109: 94-96; M. Shank, ‘The Almagest, Politics, and Apocalypticism in the Conflict between George of Trebizond and Cardinal Bessarion’, Almagest 8 (2017), 49-83: 57; M. Shank, ‘Regiomontanus versus George of Trebizond on Planetary Order, Distances, and Orbs (Almagest 9.1)’, in Ptolemy’s Science of the Stars in the Middle Ages, eds D. Juste, B. van Dalen, D. N. Hasse, C. Burnett, Turnhout, 2020, 305-386.
