This is just about the best introduction to science generally for non-scientists that I've ever read.
Bill Bryson manages to cover topics such as cosmology, geophysics, astrophysics, very basic chemistry and atomic physics, paleontology and evolutionary biology, all from the point of view of how they were discovered, thought of or argued about, and always focusing on the interesting characters involved as much as the science. He is refreshing in his honesty sometimes. Yes, it's only a basic introduction, yes, he makes a couple of mistakes, but I still learnt stuff about some of the characters and arguments involved in the history of science.
If you want something heavier, Gribbin's History of Science is much more thorough and a good read. If you want something more fun and interesting, this is great.