=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. Any attempt at varying the distances between shelves in every tier will lead to confusion in a strictly classified library. On the other hand, liberal spacing will result in the loss of a shelf in every tier, thereby reducing the total storage space by about one-eighth or one-ninth, according to the number of shelves in a tier. The balance of advantage lies, with movable forms of shelving, and it is strongly recommended that no other kind be specified or ordered.