<P> A chained library is a library where the books are attached to their bookcase by a chain, which is sufficiently long to allow the books to be taken from their shelves and read, but not removed from the library itself . This would prevent theft of the library's materials . However, it also led to crowding and awkwardness when readers had to stand side by side, each holding a book or clumping so they could share one . The practice was usual for reference libraries (that is, the vast majority of libraries) from the Middle Ages to approximately the 18th century . However, since the chaining process was also expensive, it was not used on all books . Only the more valuable books in a collection were chained . This included reference books and large books . </P> <P> It is standard for chained libraries to have the chain fitted to the corner or cover of a book . This is because if the chain were to be placed on the spine the book would suffer greater wear from the stress of moving it on and off the shelf . Because of the location of the chain attached to the book (via a ringlet) the books are housed with their spine facing away from the reader with only the pages' fore - edges visible (that is, the' wrong' way round to people accustomed to contemporary libraries). This is so that each book can be removed and opened without needing to be turned around, hence avoiding tangling its chain . To remove the book from the chain, the librarian would use a key . </P>

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