NATURAL HISTORY BUILDING 45 



are 111 feet 7 inches on the main axes and 122 feet 1 inch on the 

 diagonal axes, the enclosing walls on the east, west and north being 

 3 feet 3f inches thick. The sides of the octagon against the three 

 wings and on the south are longer than the diagonal sides in the 

 proportion of about three to two, and consist of straight walls with 

 openings into the wings and into the south projection. On each 

 faide of the portico recess in this projection there is a room about 

 15 feet square in each story, the intervening narrow space being 

 occupied by the entrance vestibule to the height of two stories, 

 fianl?:ed by two very small rooms in both, and a single long room 

 in the third story. 



Most prominent in the composition of the rotunda, which also 

 presents an octagonal shape with four sides longer than the others, 

 are four great masonry piers centering on the diagonal axes and 

 placed, therefore, one in front each of the stair towers and of the 

 two opposite shorter walls of the pavilion. These piers extend to 

 a height of 62 feet 5 inches, are 6 feet 10| inches thick in the mid- 

 dle and 7 feet 6f inches thick at the sides, and have an extreme width 

 of 34 feet. In the four spaces intervening between the piers, which 

 are 38 feet wide, are decorative screens composed of three tiers of 

 columns, corresponding to the first, second and third stories, each 

 tier surmounted by an entablature. The screens are on the longer 

 sides of the octagon, the dimension of which is greater than that of 

 the screens alone, since the inner faces of the piers are deflected at 

 the sides at such an angle that parts of their faces parallel the 

 lines of adjoining screens. The length of the longer sides so formed 

 is 47 feet, while that of the shorter sides, entirely included within 

 the faces of the piers, is 16 feet 5^ inches. 



The diameter of the rotunda is 83 feet 5^ inches measured diag- 

 onally between the faces of opposite piers, and 81 feet 6 inches on 

 the main axes between the faces of opposite columns in the screens. 

 Between the rotunda and the pavilion walls, that is to say back 

 of the piers and screens, there is a passageway or corridor 12 feet 

 4| inches wide, which extends entirely around the rotunda and 

 above the first story takes the form of a gallery at each successive 

 floor level. 



Springing from the piers at their tops and spanning the inter- 

 spaces are four semicircular masonry arches, each having a span of 

 41 feet 6 inches (being set back 21 inches from the extreme sides 

 of the piers) , a soffit width of 7 feet 6 inches and an arch ring width 

 of 2 feet 9 inches. Resting upon the piers and corbelled between the 

 arches are brick pendentives 4 feet 5f inches thick at the base and 

 struck from a sphere whose radius is 43 feet 7^ inches and whose 

 center is on a line with their bearing. When the top of the arches 

 is reached a pendentive ring 71 feet 10 inches in diameter, with 



