The much overused word genius aptly describes only a few people in the history of civilization. Leonardo da Vinci (1452-1519) unquestionably belongs in this elite group. Anyone who has looked in amazement at the Mona Lisa, The Last Supper, or the many drawings that sprang from his fertile imagination may wonder how he accomplished these astounding works of art. Fortunately for posterity, Leonardo left his Treatise on Painting, essentially a primer...