Just when modern improvements in hotel arrangements had arrived at that degree of perfection that it seemed nothing new could be added, Messrs. Stetson & Coleman, the enterprising proprietors of the Astor, have surprised the city by throwing open a novel and beautiful feature in their extensive establishment, viz., a spacious and beautiful Hall— the Astor House Exchange. The structure is entirely of glass and iron, in the form of an ellipse, eighty-six feet by fitty-one in diameter. The roof is arched elegantly, embellished with fresco painting, and supported by two columns. It is well lighted from numerous circular lights in the roof, and illuminated at night by four chandeliers from the columns and thirty-four burners xound the apartment. The building is constructed on the patent principle for iron buildings invented by Mr. Bogardus, of this city, of the firm of Bogardus & Hoppin, Centre street, the constructors of the building. The style of the architecture, is novel and graceful, exhibiting much to admire and please. The roof is a new feature in architecture ; it is constructed on the suspension principle, having girders springing in graceful curved lines from post to post, uniting strength and lightness in a most ingenious manner. This building is well worthy of great attention,—it is something in itself entirely new and without a rival in the world, both as it respects design and execution. The principle upon which the roof is constructed—the means employed and as arranged to sustain it—can be carried out to any extent. An iron building can thus be erected to extend for miles and cover acres as easily as to make one of a few feet in diameter. We commend the plan to our city authorities for the construction of iron sheds on our docks, it is the very thing required for such purposes.