NATURAL HISTORY BUILDING 41 



The line of the outer wall surface of the above construction con- 

 forms quite closely to that of the interior of the pavilion, the inter- 

 vening space, generally 12 feet 6 inches wide, forming a corridor 

 entirely around the auditorium, with large openings into the three 

 wings and the southern driveway, and access to the tower stairs and 

 elevators. With its longitudinal axis corresponding with the north 

 and south axis of the building, the doorwa3^s of the auditorium have 

 been placed on the northern side, nearest the public entrance in the 

 ground story, while the speakers' platform is on the southern side. 

 Two brick partitions with large openings, one on each side just south 

 of the tower stairs, separate the northern part of the surrounding 

 corridor from the remainder, and the former has been finished as a 

 lobby to the auditorium. Metal doors in the openings serve to com- 

 plete the isolation of the lobby, the auditorium entrances and the 

 tower stairs from the east and west wings. 



Audito7mim. — The auditorium is essentially circular in outline and 

 79 feet 6 inches in diameterj with short sections of straight wall, 

 about 26 feet wide, forming shallow niches or panels on the east, west 

 and north, and a deep recess on the south. The projection of this 

 recess is enclosed by a curved brick wall having an opening into a 

 small square room which is also reached by means of a door and steps 

 from the southern part of the corridor. The wall surface of the 

 auditorium is further broken by two small niches on the south side, 

 one on each diagonal, and two openings in corresponding positions 

 on the north side, which latter, with a doorway midway between 

 them and opposite the platform, give the means of public access to 

 the room. 



Beginning at a grade level of +6.75 in front of the speakers' plat- 

 form, the auditorium floor rises to +14, the level of the ground floor, 

 at the rear of the room, and affords opportunity for successively 

 higher rows of seats from all of which the platform is plainly in 

 view. The rising floor covers in greater part an air chamber con- 

 nected with the ventilating system. Dwarf brick, radially disposed 

 walls, built upon the floor of this chamber, support the reenforced 

 concrete slab or base of the dished floor. On this slab concentrically 

 formed steps also of concrete, 2 feet 10 inches wide, have been con- 

 structed to carry the chairs. These steps, of which there are eighteen, 

 the lower one 8 feet 8 inches from the platform, vary in rise from 

 1 inch for the lower to 9 inches for the upper, the level of which is 

 +14.75. Access to the steps or chairs is by means of four inclined 

 aisles, two of which lead directlj'^ from the side doors toward the 

 platform, while the others follow the curvature of the side walls of 

 the room. The entire floor is finished in terrazzo pavement. 



The covering of the auditorium is a low flat ellipsoidal Guastavino 

 tile dome, which springs from the four concrete piers; it does not 



