These words are to be found on the wall of Any Amount of Books on Charing Cross Road. Quite apart from being generally awesome and having an irresistible collection of Penguin Classics (literally; I did not resist), they also have this on the walls. Turns out empyrean comes from the Greek word empyrus (in or on the fire), and means "the highest heaven". I realise it's incredibly pretentious but I don't really mind - we could all do with some quiet and illimitable space in which to spread our wings and explore...Greek things. Providing said wings are not wax and we don't fall to our deaths, of course.