NATURAL HISTORY BUILDING 39 



and are secured to the ribs or projections of the T's, being locked, 

 folded over and riveted with copper rivets and burrs, no solder being 

 used. The cross- joints, which have a uniform spacing of about 8 

 feet, are locked and soldered. The ends of the standing joints at 

 the gutters are capped and the copper is soldered to the gutter lining. 

 All gutters are formed of concrete and lined with 14-ounce copper, 

 having soldered joints between the individual sheets, and soldered at 

 the outer edge into a raglet cut in the granite parapet. The cresting 

 which tops the slate work on the wings and ranges is of 16-ounce 

 copper. 



The slate is of a light gray-green color and came from Poultney, 

 Vermont. It measures generally 20 inches by 12 inches by f inch, 

 is laid about 8^ inches to the weather, and is nailed to the cinder 

 concrete. The copper cresting comes down over the upper courses 

 and at the gutters the lining is flashed up under the lower edge. 



Skylights. — The skylights covering the middle sections of the 

 wings are 32 feet 2 inches wide; in the east and west wings they 

 measure 149 feet 4 inches long, while in the north wing the length is 

 6^ inches greater. They are double pitched, and their framework 

 rests on and is riveted to the three lines of 9-inch I beams and the 

 angle curb construction already described. The curb walls, of con- 

 crete, are 14 inches high, while the end walls, due to the increased 

 pitch of the skylights over that of the roofs, are about 4 feet 6 inches 

 high at the ridge. Centered over each roof truss and extending 

 entirely across the skylights is a walk of reenforced concrete, 2 feet 

 6 inches wide, covered with copper. The spaces intervening between 

 these solid bands are divided into glazed panels, each 2 feet wide 

 with two lengths of glass to each slope, butt- jointed in the middle. 



Under each of the ribs separating the glazed panels and also 

 against the angles of the walk construction is a If by 2-inch iron 

 channel. These channels are bolted to the curb angles and to the 

 ridge and intermediate beams, and serve the double purpose of pro- 

 viding the necessary stiffness for the glazed surface and of acting as 

 drains from the ridge to the eaves to carry off any leakage or con- 

 densation. Within each of the channels, bolted to and extending its 

 entire length, is an inverted wedge-shaped channel of thin sheet 

 metal, 2 inches high, the top surface of which is about 1| inches wide 

 and provides bearing for the abutting edges of the |-inch ribbed 

 wire glass. Above the glass is a sheet copper cap secured to the 

 inverted channel every 2 feet by bolts which pass through the joint 

 between the glass of adjacent panels and, by tightening, hold the 

 glass, which is set in elastic cement, rigidly in place. A thin gasket 

 of sheet lead inserted under the edges of the copper cap where it 

 bears on the glass provides extra security against leakage. Cross- 

 gutters under the skylight at the ridge, intermediate joint and eaves 



