The floor consists of boarding one inch and a half thick, laid as in the old building, with half-inch openings between them, and resting on joists, placed two feet apart, seven inches by two and a half inches thick. These joists are carried on sleepers and props eight feet apart. The girders which support the galleries and the roof-work, and carry the brick arches over the basement-floor, are of cast-iron, and are 24 feet in length. The connections between the girders and columns are applied in the same manner as in the building of 1851. The principle of connection was originally condemned by some men of standing in the scientific world; but experience has proved it to be sound and admirable in every respect. The mode of connection is not merely that of resting the girders on the columns in order to support the roofs and galleries, but the top and bottom of each girder are firmly secured to each of the columns, so that the girder preserves the perpendicularity of the column, and secures lateral stiffness to the entire edifice. Throughout the building the visitor will notice, at certain intervals, diagonally placed, rods connected at the crossing, and uniting column with column. These are the diagonal bracings, or the rods provided to resist the action of the wind: they are strong enough to resist any strain that can be brought to bear against them, and are fitted with screwed connections and couplings, so that they can be adjusted with the greatest accuracy. The roof, from end to end, is on the Paxton ridge-and-furrow system, and the glass employed in the roof is ¹⁄₁₃ of an inch in thickness (21 oz. per foot). The discharge of the rain-water is effected by gutters, from which the water is conveyed down the inside of the columns, at the base of which are the necessary outlets leading to the main drains of the building. The first gallery is gained from the ground-floor by means of flights of stairs about 23 feet high; eight such flights being distributed over the building. This gallery is 24 feet wide, and devoted to the exhibition of articles of industry. The upper gallery is 8 feet wide, extending, like the other, round the building; it is gained from the lower gallery, by spiral staircases, of which there are eight. The greater number of these staircases are divided into two flights, each flight being 20 feet high; but in the centre transept the two staircases contain four flights of the same altitude. Round this upper gallery, at the very summit of the nave and transepts, as well as round the ground-floor of the building, are placed louvres, or ventilators, made of galvanised iron. By the opening or closing of these louvres--a service readily performed--the temperature of the Crystal Palace is so regulated that on the hottest day of summer, the dry parching heat mounts to the roof to be dismissed, whilst a pure and invigorating supply is introduced at the floor in its place, giving new life to the thirsty plant and fresh vigour to man.