...DaVinci? I read a book when I was a kid (1990-1996ish) and on the cover there was a kid on a city street and a floating metal sphere following/chasing him. I remember that in the book the school bully gets stuck back in time and they deduct that he grew up to become Leonardo DaVinci based on his knowledge of the future. It was like a kid's adventure/sci-fi book. Any ideas?