54 UNITED STATES NATIONAL MUSEUM 



latter is domical. The radial bars, of which there are twenty, con- 

 sisting of 3 by ^-inch wrought iron, extend from the curb around 

 the eye, where they are bolted to cast-iron seats embedded in con- 

 crete, to a 3J by f-inch ring of 18 inches diameter in the center. 

 About 2 feet 3 inches below this ring and attached to it by five 2 by 

 ^-inch uprights is another ring of the same diameter, from which 

 ■|-inch tie or truss rods, placed one under each of the radial bars, ex- 

 tend and are bolted to the outer or curb end of each corresponding 

 bar. By this means added rigidity is given to the skylight frame, 

 which is glazed with hammered wire plate glass in a manner similar 

 to that of the large skylights in the wings. Over the center of the 

 skylight is a sheet copper ventilator 19 inches in diameter. 



The outer covering of the upper dome consists of the same light 

 green slate that is used on the main roofs, cut in the so-called fish 

 scale pattern, and laid in 43 courses. While all the slate in each 

 course is of the same size, the size varies in successive courses, from 

 about 2 feet by 3 feet below to about 7 by 13 inches above, and there 

 is also a difference in the thickness, which ranges from 1 inch to ^ 

 inch. Of the length a little more than one-third is exposed to the 

 weather. 



NORTH ENTRANCE, VESTIBULE AND LOBBY 



The three large doorways of the north entrance, located in the 

 ground story of the north pavilion, open into a vestibule which is 

 adjoined by a capacious lobby providing direct means of access to all 

 parts of the building from this side. These two compartments are 

 separated by a structural wall pierced by three openings directly 

 opposite the outer ones and of about the same width. Each of the 

 six openings is furnished with double glazed doors, and the outer 

 ones are further protected by outside double-leaf iron grilles. All 

 of the doors and grilles are pivoted and constructed to open outward. 



Vestibule. — The vestibule is 51 feet 9 inches long, 14 feet 9 inches 

 wide and 20 feet high. Its floor level is 1 foot 6 inches below that 

 of the lobby which is reached by three runs of three steps each, each 

 run being located in front of one of the inner door openings and the 

 several runs being separated by two relatively large square dies, 

 with a narrow die at each end of the series. With the exception of 

 the ceiling and the doors and their trims, the entire room is finished 

 in Tennessee marble. The walls above the base, which is 2 feet 6 

 inches high, are of a gray variety, laid in ashlar courses 16 inches 

 wide, and have a coarse sand-rubbed surface. The wall base, steps, 

 dies and floor tile are of the pink variety, with a hone finish. The 

 floor tile of the field measure 2 feet 9 inches by 1 foot 2 inches, and 

 the entire field has border courses of the same material. The steps 

 and dies are solid and the former have molded faces. 



