I was sort of guided by Hardy, my mathematician mentor whom I spoke about earlier. Hardy wrote wonderful textbooks, including this number theory textbook, Introduction to Theory of Numbers and he wrote a wonderful little book called Pure Mathematics which is a sort of compendium of analysis for beginners, so he devoted the latter part of his life to writing these beautiful books. And I once asked him, I was then this young student, and I said, 'Don't you think it's a waste of your time writing these books instead of proving theorems?' And Hardy said simply, 'Young men should prove theorems; old men should write books.' And I think that was good advice. I mean there comes a time in your life when you're not so good any more at proving theorems and you can still write books, so he decided when he was 50 years old, roughly, that he would devote most of his time to writing books, and I have more or less followed his example. It happened accidentally that when I was 50 years old or thereabouts, I was invited by the Sloan Foundation to write an autobiography. It was in a series of autobiographies of scientists that they were bringing out, so they actually funded this, paid me in advance for the book, which became Disturbing the Universe. So I had the incentive to write it and it came at a convenient time of my life, and once I had written that book, of course, I tended to get invited to give lectures and it started a new chapter in my life simply because I was better known and I was known to a much wider public. So I began to have lots of friends in the literary world and to be invited to give talks at universities on more general subjects, and this was something that fitted naturally into my growing old, and not being able to compete with all the bright young people in this building. It was... it's clear today, when I talk with these young kids in the building, they are all in their 20s and they are writing papers faster than I can read them, so it would be stupid for me to try to compete. So I don't, and instead I do the less fashionable things, and in particular then, I do a lot of lecturing and writing. And I find it's my solution of the problem which many other scientists face. You... you solved the problem by changing from being a physicist to becoming a historian; I solved it by changing from being a mathematician to becoming a writer: it's a similar decision and history is something you can very well do as an old man.