I really thought I knew physics well, but open access to early papers of scientists reveal many unusual effects and riddles that point to new and useful ways to employ physics for space. I find these readings very useful. Much of this is taught and represented as complete and yet it is a continuum of understanding that is far from complete. Presently I am reading Heaviside on "electromagnetic mass" from the 1880's here at the archive.
Something is very wrong with physics and how it is taught in the US, anyway. Besides gravitational magnetism, there are a vast number of new concepts to explore. I recently went back to reveiw MIT solid state chemistry with Sadoway. Just like Strang and Lewin, it keeps on giving. I was very unimpressed with Stanford's offerings in AI. Oh well it is always fun to learn new things and so discovering this is a good thing. Another great time line of science is here. "The Measure of Time" by Henri Poincaré is also interesting.
ADDED: I was studying Maxwell's original papers on electro magnetics and was doing some background searches when I discovered this! at wiki sources that does the LaTeX for me, nice!