Today is the feast of St. Albert the Great, Doctor of the Church, often called the Doctor Universalis or Universal Doctor. He is the patron saint of scientists and engineers; he is usually given credit for having been the first person to isolate the element arsenic, in the sense that he is the first person on record to isolate what can be clearly identified as a pure form of arsenic (by heating arsenic compounds). He studied everything -- the entire universe of knowledge that was available to him -- everything from falcons to ant lions, from minerals to morals, not just from books but by experiments. The experiments were often crude and unsystematic, and sometimes inconclusive (to test the common claim that ostriches ate rocks, he tried to feed an ostrich gravel, but reported that he couldn't get it to eat any), but they were part of a genuinely empirical approach to the world. As he once said in talking about the phsyiology and anatomy of plants, Experimentum solum certificat in talibus ("only experience guarantees in such matters"), and, indeed, his work on plants was second to none prior to the early modern period, precisely because of his extensive observational work and careful, matter-of-fact description. He is usualy said to be, for instance, the first major figure to discuss at length the importance of light and heat for the height and spread of trees.
But he was not a mere observer, and was very much a medieval intellectual; the importance of his philosophical and theological works are slowly becoming better appreciated. Above all and beyond all others he was at the forefront of appreciating the significance of Aristotle, and of closely examining Aristotle's account, both for strengths and weaknesses; on this point at least, while Aquinas may have surpassed him, it was only because Albert had already begun to clear the way.