Economy of space is in my view best attained by fixed shelves. This dictum I will now endeavor to make good. If the shelves are movable, each shelf imposes a dead weight on the structure of the bookcase, without doing anything to support it. Hence it must be built with wood of considerable mass, and the more considerable the mass of wood the greater are both the space occupied and the ornament needed. When the shelf is fixed, it contributes as a fastening to hold the parts of the bookcase together; and a very long experience enables me to say that shelves of from half- to three-quarters of an inch worked fast into uprights of from three-quarters to a full inch will amply suffice for all sizes of books except large and heavy folios, which would probably require a small, and only a small, addition of thickness. I have recommended that as a rule the shelves be fixed, and have given reasons for the adoption of such a rule. I do not know whether it will receive the sanction of authorities. And I make two admissions. First, it requires that each person owning and arranging a library should have a pretty accurate general knowledge of the sizes of his books. Secondly, it may be expedient to introduce here and there, by way of exception, a single movable shelf; and this, I believe, will be found to afford a margin sufficient to meet occasional imperfections in the computation of sizes. Subject to these remarks, I have considerable confidence in the recommendation I have made. I will now exhibit to my reader the practical effect of such arrangement, in bringing great numbers of books within easy reach. Let each projection be three feet long, twelve inches deep (ample for two faces of octavos), and nine feet high, so that the upper shelf can be reached by the aid of a wooden stool of two steps not more than twenty inches high, and portable without the least effort in a single hand. I will suppose the wall space available to be eight feet, and the projections, three in number, with end pieces need only jut out three feet five, while narrow strips of bookcase will run up the wall between the projections. Under these conditions, the bookcases thus described will carry above 2,000 octavo volumes. And a library forty feet long and twenty feet broad, amply lighted, having some portion of the centre fitted with very low bookcases suited to serve for some of the uses of tables, will receive on the floor from 18,000 to 20,000 volumes of all sizes, without losing the appearance of a room or assuming that of a warehouse, and while leaving portions of space available near the windows for purposes of study. If a gallery be added, there will be accommodation for a further number of five thousand, and the room need be no more than sixteen feet high. But a gallery is not suitable for works above the octavo size, on account of inconvenience in carriage to and fro.