form. On the back of each blade is fixed a loop of thin iron, to which a rack is fitted; and by these means all the blades in each frame are moved simultaneously. A considerable number of these racks may also be connected, so that a large area of ventilation may be regulated at once.
ROM the total absence in this building of any internal division-walls, which in ordinary structures considerably add to their stability, it was thought desirable to introduce into the construction something to compensate for this deficiency. At several points in the length of the building, where a continuous connexion could be established transversely, the squares formed by the columns and girders on the different storeys have their four corners connected by diagonal rods, seven-eighths of an inch in diameter, having eyes at the ends, by which they are secured to the bolts connecting the different parts of the columns. In the centre of the square the four rods meet in a cast-iron ring, and are screwed up with nuts; ornamental faces are fitted into the rings, so that this addition to the construction is by no means detrimental to the general effect.
In a similar manner this diagonal bracing is introduced in a horizontal direction immediately under the floor of some portions of the galleries; of these there are twenty-two sets, and of those placed vertically there are, altogether, 220 sets in the building, and the manner of their introduction will be readily understood from the views of the interior.
HE double staircases, of which it has been mentioned there are eight in the building, consist each of four flights, about eight feet wide; two parallel ones, leading from the ground-floor to a landing, at the half-height, and the other two branching in opposite directions from the landing to the two galleries. The treads of the steps are made of a species of mahogany called sabicu, which is much harder than oak, and therefore peculiarly suited to the purpose for which it is here employed. The risers, or faces of the steps, are of deal. The stairs are supported by cast-iron girders, following the slope, the lower ones being fixed at the foot to stout timbers under the flooring, and the upper ends bolted to the cast-iron columns which support the landing. These columns are of the same pattern as the rest throughout the building, but only five inches in diameter. They are supported on concrete, and eight of them are required for each staircase. The floor of the landing is carried by lesser cast-iron girders, with flooring-joists.
VIEW OF STAIRCASE.