The general scheme of book shelves should be fixed before the plan of the building is drawn. Otherwise the space for books can not be determined and serious mistakes may be made. Between the two extremes of open wall shelves and the close stack a compromise is necessary. The large library will put the bulk of its books in a stack and bring a considerable selection of the best books into an open room. The small library will begin with books along the walls and provide cases for additions from time to time as needed. Its patrons will enjoy at first the generous spaces of the open room without an array of empty cases to offend the eye and cumber the floor. When walls are covered with books a floor case will be introduced and others when needed will be placed according to plan, till at last the floor is as full as it was meant to be, and the basement beneath having served for a time to hold the overflow, a second story of cases is put on the top of the first. This process should be planned in advance for a term of 20 years. For public access passages between cases should be five feet wide. Cases have sometimes been set on radial lines so as to bring all parts under supervision from the center. This arrangement, specially if bounded by a semi-circular wall, is expensive, wasteful of space and of doubtful value, except in peculiar conditions. It is not adapted to further extension of the building. _Size of shelf._ For ordinary books in a popular library the shelf should not be more than eight inches wide with an upright space of ten inches. Eight shelves of this height with a base of four inches and crown finish of five inches will fill eight feet from the floor and the upper shelf may be reached at a height of 81 inches or six feet nine inches. Ordinary shelves should not exceed three feet in length. A length of two and a half feet is preferred by many. A shelf more than three feet long is apt to bend under the weight of books. For books of larger size a limited number of shelves with 12 inches upright space and a few still larger should be provided. The proportion of oversize books will vary greatly according to the kind of library, a college or scientific collection having many more than the circulating library. Any reference room will contain a large number of such books and its shelves should correspond. _Movable shelves._