NATURAL HISTORY BUILDING 43 



The speakers' platform is 2 feet 6 inches high above the lowest 

 level of the auditorium floor, and 4 feet 9 inches below the floor level 

 at the entrances. It occupies the entire space of the alcove, and 

 has a curved outer edge projecting beyond the area of the alcove, 

 which is struck from the same center as the steps forming the seat- 

 ing planes in the bowl of the room. The floor of the platform is 

 supported on the surrounding walls and intermediate concrete piers 

 w^ith concrete beams, carrying an overlying 4-inch slab of rein- 

 forced concrete to which wood sleepers are secured. The final finish 

 of the floor, of the face of the platform and of the steps on both 

 sides is of cabinet oak. 



The space under the platform is used as a ventilating chamber, 

 the air having access to the room through 12 cast-iron registers, 

 measuring 14 by 20 inches, in the face of the platform rise. The 

 admission of air from the chamber under the seating part of the 

 auditorium is by means of holes through the floor of the several 

 steps. These holes are about 5 inches long by 1^ inches wide and 

 are spaced to occur under the standards or side supports of the 

 individual chairs except those on the four lower steps to which the 

 chamber does not extend. 



The combined surface of the several steps furnishes space for 

 565 chairs, which are solidly attached to the floor by means of ex- 

 pansion bolts, and, in order to obtain a compact arrangement from 

 aisle to aisle, the chairs have been made of two widths, 20| inches 

 and 22 inches. The seats are of the usual folding type, 16 inches 

 high, equipped with wire hat holders, and the width of the inter- 

 vening space between their front edges and the backs of the chairs 

 in the next row is 17 inches. There is a single standard between 

 each two adjoining chairs which provides support for the seats and 

 backs on both sides. Including the supports for the wood-covered 

 arm rests, the standards are entirely of metal; in the base of each 

 is a small register- faced box, a unit of the large system of such boxes, 

 placed over the floor openings to receive and disseminate the air 

 from the ventilating chamber. The seats and backs are upholstered 

 in brown Spanish leather and are built on and furnished with wood 

 frames, all exposed parts of which are of birch stained in imitation 

 of walnut. 



The complete isolation of the auditorium, surrounded as it is by 

 two sets of walls, makes it necessary to depend wholly upon artifi- 

 cial means for its lighting. As already mentioned, provision has 

 been made for two rows of concealed electric lamps around the cir- 

 cular eye in the dome of the ceiling, and another row is hidden 

 behind the inside ring of the arch between the auditorium and the 

 alcove of the speakers' platform. Each of the former contains 80 

 and the latter 23 lamps. In view of their positions and surround- 

 ings, the illumination of the room as a Whole is reflected and diffused. 



