=First Floor Corridors: the Mosaic Vaults.=--The North, South, and East Corridors on the first floor of the Entrance Hall are panelled in Italian marble to the height of eleven feet, and have floors of white, blue, and brown (Italian, Vermont, and Tennessee) marble, and beautiful vaulted ceilings of marble mosaic. These last will immediately attract the attention of the visitor. The working cartoons were made by Mr. Herman T. Schladermundt from preliminary designs by Mr. Casey as architect. The body of the design is in a light, warm grayish tone, relieved by richly ornamental bands of brown which follow pretty closely the architectural lines of the vaulting--springing from pier to pier or outlining the penetrations and pendentives. In all three corridors tablets bearing the names of distinguished men are introduced as a part of the ornament, and in the East Corridor are a number of discs, about eighteen inches in diameter, on which are depicted “trophies,” as they are called, emblematic of various arts and sciences, each being made up of a group of representative objects such as the visitor has seen used to distinguish the subjects of Mr. Martiny’s staircase figures. The method of making and setting such a mosaic ceiling is interesting enough to be described. The artist’s cartoon is made full size and in the exact colors desired. The design, color and all, is carefully transferred by sections to thicker paper, which is then covered with a coating of thin glue. On this the workman carefully fits his material, laying each stone smooth side down. The ceiling itself is covered with a layer of cement, to which the mosaic is applied. The paper is then soaked off, and the design pounded in as evenly as possible, pointed off, and oiled. As the visitor may see, however, it is not polished, like a mosaic floor, but is left a little rough in order to give full value to the texture of the stone. At the east end of the North and South Corridors is a large semi-elliptical tympanum, twenty-two feet long. Along the walls are smaller tympanums, below the penetrations of the vault. At the west end, over the arch of the window, is a semicircular border. These spaces are occupied by a series of paintings--in the North Corridor by Mr. Charles Sprague Pearce, and in the South Corridor by Mr. H. O. Walker. Like most of the special mural decorations in the Library, they are executed in oils on canvas, which is afterwards affixed to the wall by a composition of whitelead.