The stacks begin at the basement story, which is fourteen feet below the level of the floor of the Rotunda. They are sixty-three feet in height--the sum, that is, of the nine seven-foot stories--and are topped by an iron covering, so that any water which might by accident come through the roof would be shed without harming the books. The construction of the shelving is entirely of steel and iron. The unit of construction, as it may be technically called, is a steel column erected on a firm foundation and extending the height of the stack. There are over three hundred of them in each of the two large stacks. At the bottom of every tier above the basement is a horizontal framework of steel bars, running between the columns, the length and width of the stack, and securely anchored to the walls. These cross-pieces perform a double service: they brace the upright columns and prevent them from bending under the weight they bear, and they are supports on which to lay the decks. The cases, that is, do not rest on the flooring, but the flooring on the general system of the cases. It may be added that with the strong and simple framing that is used the stacks might very well have been carried a dozen stories higher without materially increasing the size of the columns. The ranges--by which is meant the cases for books--are of iron, divided into six compartments by partitions bolted to the columns. They are double-faced, each side being a foot deep, and have no backs. On the front edge of each partition are blunt teeth, and near the back edge is a vertical row of horns, both serving to hold the shelves in place. The ranges are at right angles with the wall, so that there is no opportunity for the occurrence of what are called “dead angles”--waste spaces in which it is impossible to put books. [Illustration: GIBBON. BY CHARLES H. NIEHAUS.] The ranges are nineteen and a quarter feet long, and in both of the larger stacks are forty-two in number, twenty-one on each side of the stack, leaving a corridor between every story the length of the gallery. Between them are aisles three feet four inches wide. Near the middle of the stack a couple of ranges are omitted to give room for staircases up and down, an elevator well, large enough to carry an attendant and a truck-load of books; and the shaft or well for the book-carriage service.