case (8 inches), plus half the width of passage-way (16 inches), multiplied by the length of the shelf (36 inches), which gives a result of 6 square feet. If the average number of shelves in the division is 9, and there are 8½ books to the foot, the capacity of the division is 230 volumes, or an average of 38 books to the square foot of floor area. In this calculation no account has been taken of the stairs, windows, doors, or cross gangway, and only a minimum width of passage-ways has been allowed. If space for these are taken into consideration, a conservative estimate of the shelving capacity of a room will work out at 25 volumes to the square foot. A book store, therefore, 50 feet by 40 in area, with cases 7 feet 6 inches in height, will shelve 50,000 volumes; and if the room be 35 feet high, and four tiers of bookcases are erected in it, its capacity is increased fourfold, to 200,000 volumes.
In the construction of bookcases and shelves wood has been generally used, but of late years iron has been introduced with considerable success. The advantages claimed for wood are that it is cheaper; it looks better; and, if the corners and edges are rounded, it does less damage to the bindings than any other material. It is contended for iron that it is fireproof; the stacks do not obstruct so much light as the solid wood cases; and that it allows free ventilation to the backs of the books. The latter (ventilation) is an important point, especially in the store rooms of large reference libraries, where long sets of books but little-
