Ευκλείδης / Euclid, Christophorus Clavius, “Euclidis Elementorum Libri XV. Accessit XVI. de Solidorum Regularium comparatione. Omnes perspicuis Demonstrationibus, accuratisque Scholiis illustrati. Auctore Christophoro Clavio”, Rome, 1574. COMPLETE: two volumes bound in one. 8vo, pp. [78], 331 numbered leaves (662 pages) , [1]. First edition of Claviuss main work, his rare and influential edition of Euclid. Contemporary full vellum. Handwritten title on spine. Water-stain on lower mainly marginal part of fist ~80 pages, occasional spotting afterwards. Contemporary manuscript strengthening spine, spine detached but still firm. Chipped part of outer front cover edge. Contemporary handwritten inscription on first blanc sheet “Hercules Lampugnanus Patricius Medio…”. Important sixteenth edition of Euclids books edited by the Jesuit mathematician Clavius. "In 1574 a new departure in the matter of format was taken. A Latin edition in two octavo volumes with rather diminutive diagrams was printed at Rome by Vincenzo Accolti. The [editor] was Christophorus Clavius (Schlüssel) of Bamberg, of the Society of Jesus, a mathematician who gave the Gregorian Calendar of New Style its present form and made all the calculations necessary for its verification. It contains the fifteen books with very full scholia, and the addition of a sixteenth, De solidorum regularium comparatione. It was reprinted at Rome in 1589 in the same form, and in folio at Cologne in 1591."-Thomas-Stanford, p. 11. Very Rare