THE BROOKLYN BRIDGE. 385 



CONSTRUCTIVE ELEMENTS OF THE EAST RIVER 



BRIDGE. 



By F. A. FERNALD. 



THE New York Bridge Company, having for its object the build- 

 ing of the suspension-bridge between New York and Brooklyn 

 across the East River, was chartered by the State Legislature April 

 16, 1867. The work was begun by this company, and continued until 

 its control was transferred to the two cities, June 5, 1874, from which 

 time until the completion of the structure it was carried on by a board 

 of trustees. John A. Roebling was at first chosen chief -engineer, but, 

 dying two years later, he was succeeded by his son and associate, Colo- 

 nel Washington A. Roebling. 



The engineer's plans and estimates were submitted in September, 

 1867, and were finally approved in the spring of 1869. The mechani- 

 cal work was begun on the site of the Brooklyn tower January 3, 

 1870. The finished tower rises 278 feet above high-water mark, and 

 measures from top to foundation 316 feet. It is faced above water 

 with granite, but is built partly of blue limestone. At the water-level 

 the tower is 140 feet wide and 59 feet thick ; the roadway passes 

 through it at a height of 119 feet 3 inches by means of two archways 

 each 117 feet high, and 33 feet 9 inches wide at the base. Where this 

 tower stands, the river-bed is a compact conglomerate of clay, sand, 

 and bowlders, in which its foundation rests at a depth of 44^ feet 

 below high-water mark. The lowest course of masonry rests on a 

 layer of pine-beams 15 feet thick, i. e., the roof of the caisson used to 

 carry down the foundation. Under the roof of the caisson are built 

 72 brick pillars, 9^- feet high, and the rest of the space is filled in with 

 a solid concrete. The Brooklyn tower was finished in May, 1875. 

 The New York tower differs from this in being three feet wider, and 

 in extending down for 78 feet below high-water mark, where it 

 reaches some spurs of the bed-rock, making the total height of the 

 tower 350 feet. The roof of the caisson was made 22 feet thick, so 

 as to support the greater weight of masonry to be built upon it during 

 its descent. This tower was finished in July, 1876. Neither has as 

 yet settled two inches. 



The four cables are each 15f inches in diameter, over two thirds of 

 a mile long (3,578^- feet), and each consists of 5,282 galvanized steel 

 wires, not twisted as in a small wire rope, but lying parallel from end 

 to end. No. 7 wire was used, which is a little over one eighth of an 

 inch thick, and each cable was made in nineteen strands. The coils 

 of wire for one strand were spliced together, so that each strand con- 

 sists of a continuous wire running back and forth across the river, and 

 at each end passing around a grooved piece of iron called a shoe. The 

 TOL. ixiu. 25 



