James B. Eads

by Louis How

In 1833, when Eads had arrived at the town, it had about 10,000 inhabitants. Though already seventy years old, it had not advanced very far beyond its original state of a French trading-post. With the introduction of steam and the waking up of the country, the growth of Saint Louis was rapid. In 1867 it had about 100,000 people. Despite a commanding situation, it could be seen that a struggle would have to be made for it to maintain the leadership among the river towns. As early as 1839 there had been a project for a highway bridge; and we are told that "the city fathers stood aghast" at an estimated cost of $736,600. In the following years there were several more abortive schemes for bridging, one of which, it is even said, would have been carried out, had not its projector died. Perhaps it is as well that he never lived to try it, for until Eads no one seems to have realized how enormous the undertaking was. Probably few others, realizing it, would have dared to go on.

In the winter of 1865-66 a bill was brought up in Congress to authorize the bridging of the Mississippi at Saint Louis. Dependence on ferries had become intolerable to the people, and often when the river was frozen even the ferries were blocked. A bridge was felt to be absolutely indispensable. However, the antagonism of rival commercial routes was so powerful that the bill was allowed to pass only after it had been so amended that it was supposed to require an impracticability. It declared that the central span of the contemplated bridge must be no less than 500 feet long, nor its elevation above the city directrix less than fifty feet. It was said at the time "that the genius did not exist in the country capable of erecting such a structure."

Still, a span of over 500 feet had been built in Holland; and the fact that there was not a total doubt as to the practicability of doing as well in the Mississippi Valley is shown by the inauguration of two rival bridge companies about a year after the passage of the bill. One of these, which was located in Illinois, after calling a convention of engineers, who considered the question for ten days, without an examination of Eads's plans, adopted a plan for a truss bridge. The other, the Saint Louis company, from the first had Eads as its chief engineer. For another year there was a sharp contest carried on between these two companies, confined, however, principally to the courts and the newspapers, until finally the Illinois company sold out to the Saint Louis company. Had the truss bridge been built, there is no knowing how long it might have stood, for the engineer who designed it did not arrange to base the foundations on the bed-rock of the river. Afterwards it was shown how necessary it was to do this; but at the time many people thought it quite superfluous, and on that, as well as on many other points, Eads met with opposition.

In every case it turned out that he had been right. No one else knew so well as he the immense power and the waywardness of the Mississippi. Good engineers supposed that the greatest imaginable scour at the river bottom in extreme high water would not remove over twenty-two feet of sand, and it was believed that there were perhaps one hundred feet of it along the east shore. But Eads had been sixty-five feet below the river's surface at Cairo, and there he had found the river bottom to be a moving mass at least three feet deep; and in cutting through the frozen river to liberate his diving-bell boats, he had found that the floating ice which goes underneath solid ice, as well as the rising or "backing-up" of the water above ice-gorges, forces the undercurrents lower than even a flood does; and he had found on cutting a wreck out of the ice that she had been held up by the gorged ice underneath her, which must therefore have been packed to the bottom. Knowing all this and much more about what goes on under the turbid surface of the river, he did not doubt that even beneath 100 feet of sand the bed-rock might at times be laid bare, and he was absolutely convinced that his bridge must be founded on it.

Moreover, he saw that on account of the exceptional force of the current in its rather narrow bed at Saint Louis, the masonry piers of his bridge must be made unusually big and strong to withstand it. Since they must be so big and sunk so very deep, it was evident that they would be so costly that the fewer there need be of them the better. The central span was required to be 500 feet; with three spans about that length the river could be crossed, and three spans would require only four piers. Steel trusses 500 feet long would have to be made extremely heavy; but Eads showed that a steel arch the same length, while quite as strong, would be lighter and consequently much cheaper. When his opponents objected that there was no engineering precedent for such spans, while he pointed out their mistake, at the same time he expressed his conviction that engineering precedents had nothing to do with the question of length of span; that it was altogether a money question. Therefore, since the cheapest method was to be carefully sought, he determined upon arches,—two abutment piers, two river piers, and three arches of respectively 502, 520, and 502 feet long.

There were many opponents to this plan; some of them people who would have opposed any bridge, as, for example, the ferry and the transfer companies. To his own company he explained away every objection that came up, as he was bound to do, in view of their confidence in him. He made the clearest of explanations of the theories involved; and even such absurd predictions as that his superstructure would crush his huge stone piers, he took the trouble to blast sarcastically. To an engineering journal he wrote three letters correcting mistakes in its accounts of his work. But he seems to have wasted little of his energy in arguing with the newspaper public. It was a question only of time till everybody should be convinced.

The most extraordinary care and pains were expended in every direction. The stone, granite, and steel were both hunted up and tested by experts, and by machines specially devised in the bridge works, though not by Eads himself. For his assistants he chose men who were of real ability and well trained, and to them he invariably gave great credit for their part in the work. The plans, after being figured out in detail by them, were gone over by the mathematician Chauvenet, then chancellor of Washington University, who found not one single error in them. Most of the big work, such as the masonry and steel, was given out on contract; and, as was natural, delays by the contractors often greatly delayed the progress of the bridge. The whole work occupied seven years.

While Eads had promised the company to prove by careful experiment, so far as was possible, everything connected with the bridge that had not already been fully demonstrated in practice, he did not pretend that in his main outlines he was without some examples. It was in his development of known ideas and his expedients for simplification that his genius perhaps most strikingly showed itself. Again and again he contrived some device so simple that, like a great many strokes of genius, it seemed that anybody should have thought of it. The massive piers were sunk to the bed-rock by means of metal caissons. These were adapted in design from some he had seen in use in France, and had examined during a trip his doctors ordered him to make in 1868. Eads himself compared them to inverted pans. They were open at the bottom, but perfectly air-tight everywhere else. They had several important features which were entirely original. Such caissons, sunk to the bottom, have the masonry of the pier built on top of them even while they are sinking; and workmen inside them keep removing the sand from underneath, and throwing it under the mouths of pipes which suck it up to the surface of the river. Evidently the caissons must be filled with compressed air to equalize the external pressure, which is constantly increasing as ever deeper water is reached; they must also have an opening connecting with the surface; and to admit of passing from the ordinary atmosphere to the denser one, there must be an air-lock. Before this bridge was built, the air-lock had always been placed at the top of the entrance shaft, where, as the caisson sank and the shaft was lengthened, it had to be constantly moved up. Eads placed it in the air-chamber of the caisson itself, where it never had to be moved; and thus, as the shaft was not filled with compressed air, less was needed, and there was less danger of leaks. Another of his useful innovations was to build his shaft of wood, and another was to put a spiral stairway into it. Indeed, in the last pier he put an elevator into the shaft. Moreover, he was the first person to run his pipes for discharging the sand, not through the shaft, but through the masonry itself; and he invented a very simple and effectual new sand-pump, which was worked by natural forces without machinery. All these improvements and various others seem to have been thought of so easily, that we are inclined to wonder why clumsier methods had ever been in use. He described them all in his reports and his letters about the bridge in a style which is not only clear but actually fascinating even to a person who has scant scientific knowledge or taste.

One of the piers was sunk 110 feet below the surface of the river, through ninety feet of gravel and sand. Eads's theories were justified by finding the bed-rock so smooth and water-worn as to show that at times it had been uncovered. This was the deepest submarine work that had ever been done, and Eads tells us in his reports many interesting experiments he made in the air-chambers. In their dense atmosphere a candle when blown out would at once light again. This was before the days of electric lighting: otherwise we may be sure that that would have been used, as so many other modern inventions were. For the first time in any such work, the last pier sunk had telegraphic communications with the offices on shore; which must have been comforting to workmen starting out to their labor in the dead of winter with two weeks' provisions. The dense air of the chambers caused not only discomfort to the ears, but also in the case of some of the workmen a partial paralysis. There was no previous experience to go by, but every precaution seen to be necessary was taken; the hours of work were made very short, the elevator was provided, medical attendance and hospital care were given free. After the first disasters no man was allowed to work in the air-chambers without a doctor's permit. And it is known that in helping the sufferers with his private means, Eads was as charitable as ever. Out of 352 men employed in the various air-chambers, 12 died. Eads, with his wonted generosity of praise, printed in his yearly report the names of all the men who worked in the deepest pier from its beginning till it touched bed-rock. It is interesting to note in passing that of all the workmen in the blacksmith's yard only the head smith himself could lift a greater weight than the designer of the bridge.

The superstructure consisted mainly of three steel arches, by far the longest that had ever been constructed; the first to dispense with spandrel bracing; and the first to be built of cast-steel. The "Encyclopædia Britannica" called them "the finest example of a metal arch yet erected." They were built out from the piers from both ends to meet in the middle; and were put into place entirely without staging from below,—once again, the first instance of such a proceeding. All the necessary working platforms and machinery were suspended from temporary towers built on the piers; and thus while the arches were being put up, navigation below was not interfered with. This throwing across of the 500-foot arches without the use of false works has been ranked with the sinking of the piers "through a hundred feet of shifting quicksands," as producing "some of the most difficult problems ever attempted by an engineer." One problem, caused by the fault of the contractors, presented itself when they came to insert the central tubes to close the arches. The tubes were found to be two and a half inches too long to go in, although they would be only the required length when they were in. It was left for Eads to insert them. Shortening them would of course have lowered the arch. Eads, who was just starting for London on financial business of the bridge, cut the tubes in half, joining them by a plug with a right and left screw. Then he cut off their ends, for the plug would make them any required length by inserting or withdrawing the screws a little. Then he went away. As it would have been much cheaper not to use this device, his assistants tried for hours to shrink the tubing by ice applications, and thus to get the arches closed; and there is a popular tradition in Saint Louis that they succeeded; but it was excessively hot weather, and they did not succeed. The screw-plug tubes, of course, were easily put in. Any part of this steel work can be at any time safely removed and replaced,—another structural feature original in this bridge.