Heinrich Cornelius Agrippa von Nettesheim ( September 14 , 1486 â `` February 18 1535 ) was a German occult writer , astrologer , and alchemist . Heinrich Cornelius Agrippa von Nettesheim ( September 14 , 1486 â `` February 18 , 1535 ) was a German magician , occult writer , theologian , astrologer , and alchemist .