of a case tilled with hooks averages about 9 cwt., hut they are so delicately poised as to be movable with but little exertion. In the lower part of the library the book capacity is trebled without inconvenience, for if one of the new cases is hung on each side of the ordinary 8 feet aisle, a width of 5 feet clear is still left in the centre for passage-way and light. A minor advantage of this system is its cheapness, for the new cases need only be supplied as required. They also meet the wants of more shelf room for any particular class of literature, which, through unexpectedly large additions, may suddenly need more room for its accommodation. Thus enormous space for the extension of the library has been obtained without taking in a single additional foot of ground.
The proper shelving of folio volumes is a difficulty often experienced. If they are placed on shelves of the ordinary width, and the shelf is not quite full, the volumes lean against each other, and speedily buckle the bindings, and allow dust to enter. The beau ideal of folio shelving is undoubtedly to lay each volume flat upon a separate shelf, but few libraries can afford the room necessary to so shelve a large collection of books. Fig. 21 shows a device used in the University Library at Strassburg. A fixed projecting ledge is made in a bookcase at a height of about 3 feet 6 inches from the ground, with a depth of about 24 inches, thus forming between each upright an open bin. A thin fixed shelf is fixed inside at a distance of, say, 6 inches from the top, and thin upright divisions are
