This Niagara railway suspension bridge has been so long in successful operation that it is difficult now to appreciate the general disbelief in the possibility of its success as a railway bridge, when it was undertaken. It was projected and executed by the late John A. Roebling. Before it was finished, Robert Stephenson said to him, "If your bridge succeeds, mine is a magnificent blunder." The Niagara bridge did succeed. [Illustration: Below the Brooklyn Bridge. From a painting by J. H. Twachtman.] We are so familiar with the great suspension bridge between New York and Brooklyn, that only a simple statement of some of its characteristic features will be given. Its clear span is 1,595½ feet. With its approaches its length is 3,455 feet. The clear waterway is 135 feet high. The towers rise 272 feet above high water and extend on the New York side down to rock 78 feet below. The four suspension cables are of steel wire and support six parallel steel trusses, thus providing two carriage ways, two lines of railway, and one elevated footway. The cables are carried to bearing anchorages in New York and in Brooklyn. The cars on the bridge are propelled by cables, and the amount of travel is now so great as to demand some radical changes in the methods for its accommodation, which a few years ago were supposed to be ample. Except under special circumstances of location or length of span, the truss bridge is a more economical and suitable structure for railway traffic than a suspension bridge. The advance from the wood truss to the modern steel structure has been through a number of stages. Excellent bridges were built in combinations of wood and iron, and are still advocated where wood is inexpensive. Then came the use of cast iron for those portions of the truss subject only to compressive strains, wrought iron being used for all members liable to tension. Many bridges of notable spans were built in this way and are still in use. The form of this combination truss varied with the designs of different engineers, and the spans extended to over three hundred feet. The forms bore the names of the designers, and the Fink, the Bollman, the Pratt, the Whipple, the Post, the Warren, and others had each their advocates. The substitution of wrought for cast iron followed, and until quite recently trusses built entirely of wrought iron have been used for all structures of great span. The latest step has been made in the use of steel, at first for special members of a truss and latterly for the whole structure. The art of railway bridge building has thus, in a comparatively few years, passed through its age of wood, and then of iron, and now rests in the application of steel in all its parts. Two distinct ways of connecting the different parts of a structure are in common use, riveting and pin connections.