The interior of the main building was divided into five avenues, the centre one about ninety feet wide, those next adjoining rather more than fifty feet, and the outside ones about forty feet wide. Iron columns, about twenty-three feet apart, formed these avenues and supported arched ribs for the roof. One end of the building was semicircular, the other forming an ornamental façade, and about the centre of the length a transept was formed. M. Horeau says: "Simplicity, grandeur, ready means of construction, and of increasing or diminishing the accommodation, and of removal if required, forming altogether a specimen of the most recent improvements introduced into the art of building--these are the principal objects which it has been sought to attain. The whole of the construction is of iron, without a single piece of wood, the foundation being executed in brick; the façade to be in metal, porcelain, and glass, the floor of asphalte, the roof to be principally covered with ornamental thick glass, in large dimensions, or ground glass with patterns. "Of the trusses or arched ribs supporting the roof there were to be but three varieties, each in three pieces, with which the whole of the building could be erected. This subdivision of the roof-trusses would have facilitated the conversion of the building for other purposes; for, taken singly, or in various combinations, they would have formed many kinds of buildings for ordinary purposes. The attached buildings placed on the north side would have shown several modes of effecting this. The ornamental spandrils of the roof-trusses would be formed in stamped-work out of copper, and gilt. "The façade shows at a glance the purpose of the building, as well as its interior disposition, in which the different widths of avenues would afford space for objects of all varieties of dimensions. The façade itself was to be formed with tracery or trellis-work of cast-iron, the lower part being covered with sheet-iron; the cornice and ornamental panels of porcelain; the medallions in coloured stone-ware; the doors and inclosures of metal, silvered and gilt; the ornamental details to be either cast or stamped; the scrolls in the panels being in coloured glass or mosaic. "The pediment is crowned with a group of figures representing the Genius of Industry crowning the Arts and Sciences; in the cornice are placed the names of all the principal cities of the world, and the names of eminent men in panels. In the medallions are represented allegorical figures of the different branches of science and industry. At the angles of the building are placed trophies, the base of which would serve as guard-houses." The engravings will serve to show the general effect of this design in its interior and exterior. ---- DESIGN BY MESSRS. R. AND T. TURNER, OF DUBLIN.