This bridge was an excellent auxiliary in the construction of the present Railway Suspension Bridge, built by Mr. John A. Roebling. It was begun in 1852, and the first locomotive crossed it in March, 1855. It is one of the most brilliant examples of modern engineering, and stands unrivaled for its grace, beauty, and strength. Seizing at once upon the natural advantages of the location, the engineer resolved to combine the tubular system with that of the suspension bridge. The carriage way was placed level with the banks of the river at the edges of the chasm. The railway track was placed eighteen feet above, on a level with the top of the secondary banks across which the two railroads were to approach it. The plan was perfect, and perfectly and faithfully executed in all its details. It is practically a skeleton tube. As the traveler passes over it in a carriage or a railway car, from the almost total absence of any vibratory motion he feels at once that he is on a safe basis, and his sense of security is complete. One feature of the construction of the bridge may be noticed as having a bearing on the question of its durability. It is well known that when wrought-iron is exposed to long continued or oft repeated and rapid concussions, its fibers after a time become granulated, whereby its strength is greatly impaired and finally exhausted. It is also known that the effect of rhythmical or regular vibrations is more destructive than the effect of those which are inharmonious or irregular. Because of this, a body of men is never allowed to march to music across a bridge, nor is a large number of cattle ever driven across at one time, lest they should, by accident, fall into a common step and so overstrain or break down the bridge. It is the difference between a single heavy blow and an irregular succession of light ones. Hence, when harmonious, regular vibrations can be broken up, the destructive influence is greatly modified and retarded. The bridge is supported by two large cables on each side, one pair above the other, the lower pair being nearer together horizontally than the upper pair, so that a cross section of the skeleton tube would be shaped somewhat like the keystone of an arch. Each of these large cables is ten inches in diameter, and is composed of seven smaller ones, called strands. These smaller strands are made of number nine wire, and each one contains five hundred and twenty wires. Each of these wires was boiled three several times in linseed oil, giving it an oleaginous coating of considerable thickness and great adhesive power. Each wire was carried across the river separately, from tower to tower, by a contrivance of the engineers, the chief feature of which was a light iron pulley about twenty inches in diameter, suspended on what might be called a wire cord. This apparatus was called a traveler, and curious and interesting was its performance as seen from below. It looked like a huge spider weaving an iron web.