=143.= The chief requirements of book-shelving are accessibility and adjustability. All authorities on library architecture are agreed that high shelves are an obstruction to quick service, and a danger to books, by placing them in a vitiated atmosphere with a comparatively high temperature. The old-fashioned wall-cases, twelve or fifteen feet high, which could only be reached by means of long ladders, are no longer recommended or installed, because of the labour they place upon the staff, their danger, and the fact that all the books on the upper shelves are not only inaccessible, but liable to a certain amount of harm. Modern librarians prefer to enlarge their floor area for the purpose of book-storage, and to provide wall and standard bookcases which are within easy reach of the floor, thus placing the entire stock at the command of both staff and readers without the labour or danger of climbing long ladders. It may be said, generally, that high wall-shelves should never be provided, unless with the provision of an iron gallery half-way up, which can be reached by means of stairs. =144.= The question of adjustability is just as important as get-at-ability. In every method or appliance which is introduced for library, or, indeed, any other work, the great principle of movability or adjustability should be preferred to fixity. The power of moving or changing without altering the character or shape of anything is of enormous advantage in every operation, and a very good illustration of the application of this power is furnished by the card catalogue, with its infinite capacity for expansion in every direction. Book-shelves should be as mobile as cards in their own way, and should be so adjustable that a new shelf can be introduced or an existing one removed at any point where such a course is possible. The only advantage which fixed wooden shelves possess is that of comparative cheapness, but this is an advantage which, in a short time, is completely swallowed up in the inconveniences which arise through the impossibility of placing books of varying sizes in strict classified order on the shelves. Besides a great sacrifice of vertical space in some places, it will be found in a rapidly growing library that the carefully gauged shelves, at eight, nine, ten, or twelve inches apart, in every tier, cannot be made to contain all the books which ought to go on these shelves in their order. The day comes when the eight-and-a-half or nine-and-a-half inch book arrives which must go on the eight or nine inch shelf, and, because there is no means of making a slight adjustment, such books must either be shelved out of their order, or placed on their fore-edges. If such shelves are arranged throughout a library at a distance of ten inches apart to provide for contingencies, they will take all sizes up to demy 8vo, but at a great sacrifice of space, especially in the fiction shelves, where most of the books average about seven and a half inches.