'The Dome, or Cupola, which surmounts the Rotunda, combines strength and lightness in an extraordinary degree. Although upwards of eighty feet diameter in the clear, its thickness is only twelve inches at the bottom, and nine inches at the top. It is constructed on the same principle as was the celebrated Cupola of the _Halle au Blé_ at Paris, and it was the first example of that mode of construction, in this country, upon a large scale. The main ribs, which are twenty-four in number, are twelve inches by nine inches at the bottom, diminishing to nine inches square at the top; they are each constructed of three thicknesses of fir planks, in lengths of nine feet, breaking joint, and firmly bolted together, every three feet; the whole planed smooth, and the heading joints fitted together with the greatest accuracy. Of the space between the ribs, by far the largest proportion is divided into sixteen glazed compartments, spreading fan wise, which diffuse an abundant light throughout the Rotunda. The remaining eight compartments are embellished with panels in stucco work, instead of glass, which adds variety, without destroying the symmetry, and relieves the eye from the repulsive glare that a skylight of that magnitude must, otherwise, produce. In the middle of the Cupola is a circular opening, surmounted by a lantern, which forms a ventilator for the Rotunda and Stabling, and is wrought, exteriorly, in the form of a coronet. Where not interrupted by the skylights, the ribs are connected by horizontal purlins, and further strengthened by iron chains surrounding the whole contour. The curvilinear plate, or curb, at the springing of the dome, measures twelve inches by nine inches, and that at the top, nine inches by nine; both are constructed in thicknesses in the same manner as the ribs above described. 'The great arches on the east and west of the Rotunda lead to the Riding House, and to a new wing of stablings, erected in 1832, for Queen Adelaide, on the site of what had been intended for a Tennis Court. They, also, contain the staircases connected with the gallery, around which are the Harness and Saddle rooms, and numerous apartments for the grooms and other servants. The southern arch opens to the pleasure grounds, and the view through the arches, from the entrance gateway, across the Rotunda, is singularly striking. The stables, surrounding the area, forty-four in number, are so arranged that, when the doors are open, a spectator, standing under the central part of the Cupola, may see into every stall, without changing his situation. The fronts of the stables, and the arcades of the surmounting gallery, are finished in a corresponding manner to the dome, and this gives an harmonious character to the whole interior.