Leonardo da Vinci, born April 15, 1452, in Italy, was much more than the painter of the Mona Lisa. He was also one of history's greatest scientific thinkers. Leonardo filled over seven thousand pages of notebooks with drawings and ideas. He studied anatomy by dissecting human bodies, something few people dared to do at the time. His drawings of muscles, bones, and organs were the most detailed in the world for centuries. Leonardo was fascinated by flight. He spent years watching birds and bats. He measured their wingspans and studied how they changed direction in the air. He designed a flying machine called an ornithopter that flapped its wings like a bird. He also sketched a device that looked like a helicopter, with a spinning blade on top. Neither machine was built during his lifetime. Modern engineers have tested his designs and found that some would actually work. Leonardo also designed an early diving suit, a self-propelled cart that worked like a robot. A bridge that could be assembled without nails. He wrote all his notes in mirror writing, from right to left. Scholars believe he did this to keep his ideas private.