Engineering Wonders of the World
Volume I

260 ENGINEERING WONDERS OF THE WORLD. The Pennsylvania tunnels have a larger purpose, since they are part of the greatest railway in America, and are intended to carry its passengers from the company’s tracks in New Jersey directly into the city, whereas hitherto they had to cross by ferry. The East River tunnels of the same system will serve the passengers of the affiliated Long Island Railway reaching out into all parts of Long Island. The Hell Gate Bridge is to be an integral part of this system, and over it the trains from New England may enter New York, or pass on to New Jersey, bound for the West. Thus it may be understood that the great works of construction which have been men- tioned bear a most immediate relation to the daily, hourly life of the great city. They are not mere engineering marvels ; they are admir- able parts of the city’s complex arterial system, carrying the flow of its life-blood. THE FAMOUS BROOKLYN BRIDGE, THE FIRST BRIDGE BETWEEN NEW YORK AND BROOKLYN. Ferry transportation made its drawbacks felt so early that even seventy years ago there was talk of building a bridge between Brooklyn and lower New York. The natural limitations of ferry service could not be improved away. But the building of a bridge was a stupend- ous problem. The deep, wide river and the busy shipping gave no opportunity for piers in the channel, while a span across the whole width was utterly beyond past achievements. So the talk about bridging was largely fanciful speculation ; no one had a workable idea for the undertaking. Then in the late ’sixties a man who had built several large suspension bridges, John A. Roebling, said that he could and would bridge the East River—and he did. He himself died during the work—indeed, before it was fairly started—but his son, aided by the genius of one or two others, carried out his plans. In 1884 the bridge was finally opened to traffic. A technical picture of the bridge is afforded by Fig. 3, a drawing of its cross section. It shows two railway tracks (for “ elevated rail- way ” trains), two roadways outside carrying also trolley-car tracks, and in the middle a footwalk. There are four main longitudinal Fig. 3.—CROSS SECTION OF THE BROOKLYN BRIDGE, SHOWING TWO ROADWAYS, FOOTWAY, TWO ELEC- TRIC CAR TRACKS, AND TWO ELEVATED ROADWAY TRACKS. The four cables carrying the bridge are 15f inches in diameter, and contain 14,000 miles of wire. trusses located between the roadways, and two smaller trusses along the outer edges. The main cables are directly over four of these six “ stiffening trusses,” and the latter are hung to the cables by suspender ropes or rods, one every 7| feet along each cable. The purpose of the stiffening trusses will be apparent ; for were the roadway hung from the cables alone, a heavy load at one point along the bridge would produce a sharp sag there, and as this load moved the sag would travel along with it. This would not only make hard hauling, but it would “ work ” the various parts of the bridge very severely, besides taxing the cables unduly through the sharp bending at every such sag. The trusses prevent this localized sagging, and distribute the local load over a considerable length of the cables. The Brooklyn Bridge has special claim on our esteem because almost every feature and method employed in the later suspension bridges is copied from it with but minor im- provements. The diagonal stays, which are so noticeable (they are attached to the towers by the curious fastenings sketched in Fig. 4), have not been copied, however, and remain a characteristic of the Brooklyn Bridge. Since the methods of building the later bridges are