The Feynman Lectures on Physics is a classic multi-volume textbook, delightful and inspirational to read, a formative experience for many a proto-physicist (e.g., me, circa 1970). Recently I found on the library shelf an audio-CD set of the original Richard P. Feynman lectures, as given at Caltech in 1962-64 — "live" in the Master's Voice with that incorrigible Brooklyn accent. It's huge fun to listen to the stage directions ("Can I have the lights, please?"), the rattling of blackboards, the low muttering as he fights balky equipment during desktop demos, the self-criticism as he draws diagrams, the agile recovery from algebraic mistakes, and the silly jokes (e.g., after mentioning Michael Faraday: "Incidentally we have a good day today!").
And then there are the marvelous pedagogical asides that Feynman offers to the class, remarks that never made it into the written transcripts. For example:
That's one of the secret methods of theoretical physics. You can always do a different problem if it's easier to figure out. Then you can come back and make it more complicated.
Or, discussing semiconductor technology in 1963:
Things are changing every day and I will tell you what the applications are up to the latest moment. It is perfectly obvious that by studying these materials there will be new and more wonderful things to make and to do as time goes on. This lecture is, of course, not necessary — it's just for your own interest, in telling you about these things, so that you know at least some of the things you're learning about have got something to do with something.
You've seen this before in quantum mechanical equations or in oscillators or eigenvalues of vectors or whatever you want to call it. Anyway the result is that it has no solution unless the determinant is zero. You see by the way that as you learn things, you really learn much more than you think. Each time that you've gotten something, you find out that you can understand what somebody else is doing in a completely different field!
Above all, there's the incomparable excitement that Dick Feynman constantly conveys — the joy of discovery, the pure love of understanding.