In the 19th century, books were especially popular gifts — cheap enough to be owned by the middle class, but enough of an investment that people kept them for decades, then passed them down to the next generation or donated them to libraries. Increasingly, libraries must decide which of these books to clear out and digitize to make room for more. In the process, they risk losing the record of individual reader’s annotations and inscriptions. In Book Traces: Nineteenth-Century Readers and the Future of the Library (Bookshop|Amazon), University of Virginia associate professor of English Andrew Stauffer chronicles a project to uncover and catalogue the “shadow archive” of history hidden in such volumes. This is part of a complete episode.