NATURAL HISTORY BUILDING 109 



extend through which are on a line with the inner large brick piers 

 to which they are joined, the intervening ones stopping 3 feet short 

 of the single stacks against the macite partition, but all other passage- 

 ways are 2 feet 6 inches wide. A unit bay arrangement is thereby 

 carried out, the circulation being complete within each bay, but in 

 going from one bay to another it is necessary to return to the main 

 passageway adjacent to the outer walls. All of the double stacks 

 on each side of the compartment terminate at the outer end on the 

 same line, but the width of the main aisle varies from 3 feet in front 

 of the piers to 4 feet between them where single stacks occur. 



The form of stack adopted is distinguished by the fact that, whether 

 single or double, the shelving, which is of the bracket type, is sup- 

 ported from single rows of uprights, making the adjustment of 

 shelves especially convenient and resulting in a considerable gain iii 

 the amount of shelf space available. The uprights measure 17 feet 

 6 inches high. Those at the ends of all stacks are of angle irons, 

 while the intermediate ones are of T irons, the measurements of both 

 being the same, namely 2 inches by 2 inches by I inch. In the single 

 stacks single irons are used, but in the double stacks each upright 

 consists of two such irons, spaced 1 inch apart at the ends of stacks 

 and ^ inch apart at intermediate points, and secured together. The 

 uprights are fastened to the floor by means of iron shoes, while at 

 the top they are braced between the ceiling girders by channel irons 

 and between the walls by tie bars. 



On the side facing the passageway each of the uprights through- 

 out its entire height, except for the 6 inches occupied by the mezza- 

 nine floor, is pierced with a continuous line of holes, each | inch long 

 by f inch wide and spaced 1^ inches on centers, which is the minimum 

 dimension for the adjustment of shelves. The brackets, to which the 

 shelves are attached, are triangular and consist of a solid piece of 

 12-gauge steel, provided on the back edge with a hook at the top and 

 a point at the bottom both of which engage the holes in the upright. 

 The shelves are of three widths, 12 inches, 16 inches and 18 inches, 

 and vary in length from 20^ inches to 53| inches. They are made 

 of 14-gauge steel plate, and all 16 and 18-inch shelves, as well as all 

 12-inch shelves over 37 inches long, are reenforced their entire length 

 with a f by 1^-inch channel iron riveted in the middle of the under 

 side. As an additional means of strengthening the shelves, their 

 front edges are turned down in the form of a flange, 1 inch wide, 

 which serves for the attachment of labels, and the edges at the back 

 are bent up to provide a stop, 1 inch high, which prevents the jars 

 or bottles being pushed from the shelf. 



The mezzanine floor is constructed of black slate, 1 inch thick, set 

 in a steel framing which is attached to the walls and to the uprights 

 of the stacks. The under side of the steel beams is 8 feet above the 



