Visionary Leonardo da Vinci's Notebooks are available free online
For hundreds of years most of Leonardo da Vinci's notebooks were hidden from the public. They were seen only by historians ans specialty collectors. If you've ever wondered what was going on in his mind, the best place to start are his collection of renaissance notebooks with his inventions and ideas.
This is a great resource tool for anyone interested in his work including his original ideas for the airplane, helicopter, parachute, submarine and the automobile.