I have taken the occasion of a second edition for enhancements and re?- ments that preserve the spirit of the original. I have more fully portrayed the remarkable relationships between symmetry group generators and their Lie bracket and the dynamical invariants of those symmetries and their Poisson bracket in Chapter 3. The radical departure of quantum waves from classical waves is more sharply drawn in Chapter 5. The spectacular way in which the states of the hydrogen atom unfold from its symmetries is the centerpiece of qu- tum Kepler motion. I now lead readers more deliberately through...