I am honoured, as a non-engineer, to be invited to give this lecture. Engineers, like the medical profession, attract, in equal measure, respect and suspicion. We all know that one day we will fall into your hands-we have to cross your bridges, live in your radical new buildings, cooperate with your exciting machines, just as we all know that, one day, we will end up on some surgeon’s table or in some physician’s clutches. And yet you are men and women like us, not inhabitants of the rarified world of n dimensional space like mathematicians, or of the vast expensive labyrinths constructed by experimental physicists for their own pleasure underneath the Alps. You are practical men dealing with practical needs, and we think we know what you are talking about when you get together in your meetings.