I love old books, and was amusing myself by reading a geology text from around 1880. It was my first exposure to that science. It amused as I started that I might end up with a good education, a hundred years out of date. As I continued I came to suspect that geology hasn't really changed all that much.

As much as I'd like ~50 year copyright on all classes of works, the good news is that those 1880s texts really are very good. (See also the telegraphy love story that just came across HN.)