on optics and astronomy. Albert the Great (1193–1280), Doctor Universalis, was one of the most prominent representatives of the philosophical tradition emerging from the Dominican Order. He is one of the thirty-three Saints of the Roman Catholic Church honored with the title of Doctor of the Church. He became famous for his vast knowledge and for his defence of the pacific coexistence between science and religion. Albert was an essential figure in introducing Greek and Islamic science into the medieval universities, although not without hesitation with regard to particular Aristotelian theses. In one of his most famous sayings he asserted: "Science does not consist in ratifying what others say, but of searching for the causes of phenomena." Thomas Aquinas was his most famous pupil. John of Sacrobosco (c. 1195 – c. 1256) was a scholar, monk, and astronomer (probably English, but possibly Irish or Scottish) who taught at the University of Paris and wrote an authoritative and influential mediaeval astronomy text, the Tractatus de Sphaera; the Algorismus, which introduced calculations with Hindu-Arabic numerals into the European university curriculum; the Compotus ecclesiasticis on Easter reckoning; and the Tractatus de quadrante on the construction and use of the astronomical quadrant. Jordanus de Nemore (late 12th, early 13th century) was one of the major pure mathematicians of the Middle Ages. He wrote treatises on mechanics ("the science of weights"), on basic and advanced arithmetic, on algebra, on geometry, and on the mathematics of stereographic projection. Villard de Honnecourt (fl. 13th century), a French engineer and architect who made sketches of mechanical devices such as automatons and perhaps drew a picture of an early escapement mechanism for clockworks. Roger Bacon (1214–94), Doctor Admirabilis, joined the Franciscan Order around 1240 where, influenced by Grosseteste, Alhacen and others, he dedicated himself to studies where he implemented the observation of nature and experimentation as the foundation of natural knowledge. Bacon wrote in such areas as mechanics, astronomy, geography and, most of all, optics. The optical research of Grosseteste and Bacon established optics as an area of study at the medieval university and formed the basis for a continuous tradition of research into optics that went all the way up to the beginning of the 17th century and the foundation of modern optics by Kepler. Ibn al-Baitar (died 1248), a botanist and pharmacist in Al-Andalus, researched over 1400 types of plants, foods, and drugs and compiled pharmaceutical and