118 UNITED STATES NATIONAL MUSEUM 



ment, a greater amount of storage space has been secured than would 

 have been the case had the corridors been made narrower and the 

 room widths increased proportionally. 



ATTIC STORY 



In the attic story the wing sections only are accessible for museum 

 purposes. They have the same distribution of floor space as the 

 wings in the third story, practically all of which, with the exception 

 of such parts as are occupied by the enclosures of the ventilating sys- 

 tem, is available for use. The lighting in the main is excellent and 

 well diffused, being furnished by the continuous series of windows in 

 the side walls of the light wells. The ventilation is also good, being 

 more direct than in the lower stories, and the false ceiling of Sackett 

 board tends to mitigate the direct effect of the sun's rays on the roof. 

 These conditions make the attic more habitable than such places gen- 

 erally are, and add to its utility for storage the advantages and con- 

 veniences required for the handling and sorting and even for the 

 examination of collections. 



The ijvalls of the light wells are only 3^ inches thick and their 

 faces, as in the third story, are subdivided into uniform panels or 

 bays by attached piers. The spaces at the sides average about 33 

 feet 1 inch wide, while those at the ends measure 48 feet 2 inches wide 

 in the east and west wings, and 36 feet 6 inches wide in the north 

 wing. The height of the story to the under side of the false ceiling 

 is about 9 feet at the sides of the light wells and about 8 feet 5 inches 

 at the outer edge of the decked portion of the roof. Intermediate 

 members of the roof trusses, in the form of an open framework cor- 

 responding to each truss, extend crosswise of the spaces at intervals 

 of 18^ feet, measured between centers, and divide them into regular 

 sections, leaving, however, an unobstructed thoroughfare, about 6 

 feet wide, adjoining the sides of the light wells. 



Each of the wings communicates with the third gallery of the south 

 pavilion by means of a large opening on each side, provided with 

 double steel doors. The freight elevators, the southern passenger 

 elevators and the tower stairs all extend to this story, which is also 

 reached by four service stairs from the third story, two located in the 

 north wing and one each in the east and west wings. 



The total amount of floor space in the attic story, not including 

 the south pavilion, is about 48,436 square feet, from which about 

 2,819 square feet should be deducted on account of the ventilating 

 enclosures, the stairs and the elevators. The truss members must also 

 be taken into account, and to a certain extent the heating mains, 

 though these are mostly raised some distance above the floor. In 

 view of the isolation of the wings and of their height above the 

 ground, which greatly diminishes the annoyance from dust, it has not 



