Another kind of source of inspiration and a subtle form of knowledge that may be hard to gain from elsewhere is older physics books, for example Richtmyer and Kennard's Introduction to Modern Physics (4th ed., 1947). Often written in an impeccable style, these books contain information that is now considered of historical value only and yet may be invaluable in providing the exactly those - historical - details that are omitted or glossed over in more modern texts.