and so it will not be necessary to keep a stock of shelves of varying sizes on hand suitable for odd places. Shelves are generally made of 1-inch wood, and when planed and ready for use may be taken as from ¾ to ⅞ of an inch in thickness. With wood of this thickness it will be found that a shelf 42 inches in length may be used without it warping or sagging in the centre under the weight of heavy books. On the other hand, shorter shelves are better for keeping the books upright, and so we are led to the conclusion that for practical purposes a length of between 30 and 36 inches is the best.
The shelving for the folio and quarto volumes may well be provided in the wall cases. In constructing these it will be best to make the lower part of the case of greater depth, so that a ledge of about 8 inches in width may be formed at a height of, say, 3 feet from the floor. The total height of the case will, of course, be the same as the stack cases, but the depth of the top portion above the ledge should be 13 inches, and below 21. Cases of these dimensions will give accommodation for the largest books likely to be found in ordinary libraries, and if any of a larger size should be acquired, they must be placed in a specially constructed case.
We have spoken so far of one storey only of bookcases, 7 feet 6 inches in height; but if these are placed on the floor of a lofty room, it will at once be seen that similar rows may be built on the top of them, if a floor of thick hammered glass or perforated iron-work is placed between.
