Book excerpt: "When the seeds of modern thought were planted in 15th-century Italy, no one sowed more of them than Leonardo da Vinci. For the millions of readers today who ponder the mysteries behind his sketch-filled notebooks and enigmatic paintings, National Geographic presents Leonardo's Universe. This richly visual reference reveals the spellbinding Renaissance world like no other, painting a vivid picture of the historic backdrop of this astounding period that revolutionized art, science, philosophy, and politics."--BOOK JACKET.