http://books.google.it/books?id=HBcfM3mCOjgC&printsec=frontcover&dq=lettere+copernicane&hl=it&sa=X&ei=r48ET-DOIsLoOeXrzbYB&ved=0CDAQ6AEwAA#v=onepage&q=lettere%20copernicane&f=false
