Albertus Magnus

I'm a little late (his feast day is November 15), but I do want to do something to mark the occasion. Albert the Great, the Doctor Universalis, is the patron saint of scientists and best known for being the teacher of Thomas Aquinas. Discussing the life of plants, he laid down the principle, Experimentum solum certificat in talibus (experience alone is the judge in such matters); and in discussing minerals, he said, "The aim of science of nature is not simply to accept the statements of others, but to investigate the causes that are at work in nature." There's an enthusiastic biography of him online. One of the most famous paintings of the Doctor Universalis is here.