h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

I've been reading the notebooks of Leonardo da Vinci. He knows the basic concept behind a television...he says that images stay in the eye for a while. He did the first helecopter. He talks about scuba gear, although he doesn't get very specific about it because of how people could use it for bad, like attacking ships from underneath. He is so smart, but where does he get his information from? He is extremely intelligent by making such conclusions from his observations. Still puzzled about him...