The external walls of the building are constructed of cast-iron framing and panel-work, into which are inserted the sashes of the windows and the louvers for ventilation. The glass is one-eighth of an inch thick, and was manufactured at the Jackson glass works, New York, and afterward enameled by Cooper & Belcher, of Camptown, N. J. The enamel, with which the whole of it is covered, is laid upon the glass with a brush, and after drying, is subjected to the intense heat of a kiln, by which the coating is vitrified, and rendered as durable as the glass itself. It produces an effect similar to that of ground glass, being translucent, but not transparent. The sun’s rays, diffused by passing through it, yield an agreeable light, and are deprived of that heat and glare which belong to them in this climate. In the absence of a similar precaution in the crystal palace at Hyde park, in England, (of which an account will next be given,) the roofs of which, as well as walls, were inclosed with transparent glass, it was found necessary to cover the interior of the building with canvas, to produce the required shade.

At each angle of the building there is an octagonal tower, eight feet in diameter and seventy-six feet in hight. These contain winding stairways, which lead to the galleries and roofs, and were intended for the use of the officers and employees of the association. Twelve broad staircases, one on either side of each entrance, and four beneath the dome, connect the principal floor with the gallery. The latter are circular in part, and consist of two flights of steps with two landing-places. The flooring of the galleries is made of closely matched planks, while those forming the floor of the first story are separated by narrow intervals, in the same manner and for the same purpose as in the London building. Over each of the principal entrance halls, the galleries open upon balconies, which afford ample space for placing flowers, vases and statues for decoration. Above the balconies, the ends of the naves are adorned with large fan-lights, corresponding to the semicircular arches within. On each side of the entrances there are ticket offices, and adjacent to them rooms are provided for the officers of the association, telegraph, &c.

The rapid and unexpected increase of the applications of exhibitors, induced the association to erect a large addition to the building already described. It consists of two parts, of one and two stories respectively, and occupies the entire space between the main building and the reservoir. Its length is four hundred and fifty-one feet and five inches, and its extreme width is seventy-five feet. It is designed for the reception of machinery in motion, the cabinets of mining and mineralogy, and the refreshment rooms, with their necessary offices. The second story, which is nearly four hundred and fifty feet long, twenty-one feet wide, and extends the whole length, is entirely devoted to the exhibition of pictures and statuary. It is lighted from a skylight, four hundred and nineteen feet long, and eight feet and six inches wide.

The decorations of the building were intrusted to Henry Greenough, Esq., brother of the lamented sculptor of the same name. Mr. Greenough has made art his study, and in its pursuit has resided long in Italy. The leading idea in the plan of decoration, has been to bring out the beautiful construction of the building; to decorate construction rather than to construct decoration. To do this, and at the same time to preserve a general harmony of effect, has given Mr. Greenough ample opportunity to display his knowledge of the resources of his art. The result is surprisingly beautiful. The colors employed on the exterior are mixed in oil, the base being the white lead manufactured by the Bellville Company. The exterior presents the appearance of a building constructed of a light-colored bronze, of which all features purely ornamental are of gold. The interior has a prevailing tone of buff, or rich cream color, which is given to all the cast-iron constructive work. This color is relieved by a moderate and judicious use of the three positive colors, red, blue and yellow, in their several tints of vermilion, garnet, sky-blue and orange, (certain parts of the ornamental work being gilt,) to accord with the arrangement of colors employed in the decoration of the ceilings. The only exceptions to the use of oil colors are the ceilings of the American lean-to and the dome; these decorations are executed on canvas. The effect of the interior of the dome, (designed by Sr. Monte Lilia,) is particularly splendid. The rays from a golden sun, at the center, descend between the latticed ribs, and arabesques of white and blue, relieved by silver stars, surround the openings.

The building is supplied with gas and water in every part. The gas was, at first, designed for the use of the police, in protecting the property by night; but was so arranged that now, when the building is opened in the evenings, it affords the most ample light throughout the entire edifice. The water is accessible at numerous points, with convenience for drinking, also for the attachment of hose, in case of fire.

The whole quantity of iron employed in the construction amounts to eighteen hundred tuns; of which three hundred tuns are wrought and fifteen hundred tuns cast iron. The quantity of glass is fifteen thousand panes, or fifty-five thousand square feet. The quantity of wood used amounts to seven hundred and fifty thousand feet, board measure.

The general mode of erection by base pieces, columns, connecting pieces and girders, is the same with that of the great Hyde park building, but the construction of the arched nave, and of the dome, is of course entirely peculiar, and the general effect of the building is completely different. The London building was certainly deficient in architectural effect. The form of the New York edifice affords the requisite scope for a pleasing variety of embellishments, by which all monotony can be avoided, and allows a very economical use of the ground. The dome, independent of its effect in the interior arrangement of the edifice, will give hight and majesty to the exterior.

To complete the explanation of the construction of the building, we recapitulate its principal dimensions.

Ft. In.
From principal floor to gallery floor, 24
From principal floor to top of second tier of girders, 44 4⅜
From principal floor to top of third tier of girders, 59 10
From principal floor to ridge of nave, 67 4
From principal floor to top of bed-plate, 69 11
From principal floor to top of upper ring of dome, 123 6
From Sixth avenue curb-stone to top of lantern, 151
From Sixth avenue curb-stone to top of towers, 76 9
Area of first floor, 157,195 square feet.
Area of second floor, 92,496 square feet.
Area of second floor, 92,496 square feet.
Total area, 249,692 or 5¾ acres.

The magnitude of these proportions alone, is calculated to excite feelings of profound awe in the spectator’s mind; and when we see added the gorgeous but subdued chromatic decoration with which the interior is ornamented, and the innumerable works of art and industry with which it is so richly filled, we may well be proud of an erection which is destined to confer lasting honor on the American name.