NATURAL HISTORY BUILDING 91 



or indirectly through other channels, such as the stair wells and ele- 

 vator shafts, and discharge it through openings in the roof. 



The space enclosed between the skylight and ceiling light in the 

 middle of each wing and the entire attic space OA^er both ranges serve 

 as exhaust chambers into which the air passes on its way to the fans. 

 There are six of these fans, of the full-house pattern made by the 

 American Blower Company, arranged in pairs at the outer ends of 

 the three wings and identical in all respects except that those in the 

 east and west wings measure 6 feet, while those in the middle wing, 

 where the height is less, measure only 5^ feet. The smaller size of 

 the latter is, however, compensated for by giving them a maximum 

 speed of 300 revolutions a minute, the former making only 250 revolu- 

 tions. Each pair is operated electrically by a 25 horse power Diehl 

 motor, direct connected to one of the fans which may be run singly 

 if desired, the shafts of the two being united by a flexible clutch 

 coupling in such manner that the other fan may readily be thrown 

 out of service. The discharge capacity of each pair is 70,000 cubic 

 feet of air a minute, making a total for all of 210,000 cubic feet. 

 Each pair of fans is contained in a brick house adjoining the sky- 

 lighted space at its outer end and communicating with it by means 

 of a large rectangular opening supplied with dampers. The ranges 

 connect Avith the fan houses through large ducts, while the discharge 

 openings in the roof are above the fans, and measure 18 feet 10 inches 

 long by 3 feet wide. 



To check direct heat radiation from the roofs in summer the 

 side and outer end sections of each of the attics in the wings are 

 provided with false ceilings of |-inch Sackett board, which under- 

 lie the roof with an interspace of about 5 inches. This ceiling 

 begins about 5 feet from the eaves and on the sides stops about 2 

 feet 3 inches from the walls of the skylight chamber, whence a 

 curved galvanized iron deflector carries around the longitudinal I 

 beams projecting below the roof in the plane of the walls, and con- 

 tinues the interspace until it opens into the chamber which it does 

 throughout the entire length of the latter. The ventilating flues 

 and ducts communicating with the attics are located in the wall 

 chases and in the floors about 2 feet from the eaves. All of the 

 air issuing from them and from other openings into the attics is 

 drawn into the exhaust chambers and thence into the fan houses by 

 way of the shallow space above the false ceiling, but with the open- 

 ing of any of the hinged panes in the transoms of the third story a 

 certain amount of air will enter the chambers directly from that 

 source. 



The low attic spaces over the ranges present wholly different 

 conditions, and are kept entirely closed at the ends except when 

 access is required to the pipes or wires which they contain. Into 



