Begun 1870 and completed in 1883, the Brooklyn Bridge was 50% longer than any other bridge at the time, and the towers were the tallest structures in America. It was designed by John Augustus Roebling and built by his son Washington and his son’s wife Emily who directed the daily work for thirteen years. Without the computers necessary to optimize the design, Roebling worked to requirements six times what he calculated were sufficient, enough to withstand aerodynamic strains that were then unknown. Even when contractors used inferior cabling, the bridge was merely four times stronger than necessary.
The roadbed itself is a lattice of crossbeams every seven feet six inches, and six perpendicular trusses that run parallel along the 1595 foot length of the bridge, all connected by diagonal braces to create a stiff platform 86 feet wide and weighing 6740 tons. The platform is lifted by steel ropes up to a parabola of twin cables on each side which in turn deliver the weight to the tops of the stone towers, 276 feet high, anchored 78 feet into the bedrock below the river. And then the cables run 930 feet back from each tower to four elaborate anchors, each with 11,700 tons of pull to keep the bridge erect and stable. While other suspension bridges failed around the world, this one stood, not only a marvel of modern engineering but a testimony to the optimism of the age and the courage of one engineer.
But—here’s the problem—how do you measure the width of the river in the first place? With nothing but a household measuring tape, how would you determine the width of a river you could not cross?