92 UNITED STATES NATIONAL MUSEUM 



these large vacuum chambers the air is pulled from the wall flues 

 and floor ducts, but instead of being carried directly to the fans, it 

 is, by an extensive system of pipes, made to assist in preventing 

 direct heat radiation from the roofs to the third story ceilings. The 

 arrangement is as follows : Four large galvanized iron ducts traverse 

 the attics longitudinally, one on the east side leading to the eastern 

 fans, one on the west side leading to the western fans, and two on 

 the north side, both much shorter than the others, leading to the 

 northern fans. From the place of origin, where they are relatively 

 small and round, about 15 inches in diameter, the ducts increase 

 gradually in size and change to a rectangular shape, becoming quite 

 large where they reach the wings. At twelve different points in 

 each length of 18^ feet, and placed only a few inches from the roof, 

 are series of inlets opening into branches of varying length, con- 

 nected with the main ducts and so proportioned that the amount of 

 air drawn from all parts of the range spaces will be approximately 

 the same, this result being accomplished by decreasing the size of 

 the branches in the direction of the fans. The branches are, 

 furthermore, supplied with dampers for their separate control. In 

 this manner all of the air entering the chamber is lifted to the 

 under surface of the roof, and thereby kept in circulation until it is 

 withdrawn. In passing out of the ranges, each duct first opens into 

 a large brick chamber in the adjoining wing, which is connected to 

 the fan house across the ceiling of the wing by another large iron 

 duct, provided with a regulating damper. 



The auditorium, boiler and engine rooms, alcoholic specimen room 

 and several toilet rooms in the ground story have each a separate 

 ventilating system, as described below. This story has direct con- 

 nection with the general fan system through flues in each alternate 

 pier chase in the middle wing and two ranges, which were intro- 

 duced principally with the object of carrying warm air to the third 

 story to assist in its heating. The inlets, covered by 12 by 14-incli 

 iron registers, are located a little over 2 feet above the floor. The 

 flues have openings in both the third story and the attics, but, as 

 they convey unpleasant odors and noxious fumes from the preserva- 

 tives and poisoning materials used on the specimens stored in the 

 ground story, it has been found necessary to keep the openings 

 into the third story closed. They undoubtedly serve a useful pur- 

 pose in those parts of the ground story from which they lead, but 

 for the ventilation of this story dependence is mainly had upon the 

 window openings in conjunction with the transoms of the room 

 partitions and the registers in the bottom rails of the doors. 



There is no direct connection between the first and second stories 

 and the fan system in the attics, except through flues in certain of 

 the pier chases with openings near the floor in the first story. These 



