The Official Descriptive and Illustrated Catalogue of the Great Exhibition, Vol. 2, 1851 (p. 538)
The illustration above it a bit difficult to read: it shows the upper cover of a book, in the center, and on the top and sides are mirrors (angled around 30 degrees?) reflecting the spine, foreedge and top edge. Judging from the joint at the top right corner, it looks like this display was custom constructed for the exact size of this book. I rarely see mirrors used in the display of books, and never three mirrors as pictured above of this Royal Bible bound by Messrs. Leighton. It seems a good idea for displaying super-extra bindings — the kind of books that the exterior decoration is their primary value. Obviously, it doesn’t solve all the problems of displaying these kind of books, but it does present more than just the upper board, and in a nineteenth century manner.