Kitabı oku: «James B. Eads», sayfa 4

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.

Although Eads took care to protect his special innovations by patent, he was most willing to explain them with care to other engineers and to have others profit by his improvements; and several of the mechanical novelties of his bridge are now in the commonest use, and have been taken advantage of even in such famous structures as the Brooklyn Bridge.

During the building of the bridge Eads spent many months in enforced absence, but while in Europe he always had his labor in mind, and, as I have said, brought home from France one of his most useful appliances. During his absence he left absolutely trustworthy and efficient engineers in charge of the work, and before leaving home he provided for accidents that might occur. So much work was done in the winter that great barriers had to be built to keep it clear of floating ice. One curious detail connected with the bridge is that the Milwaukee, one of the double-turreted gunboats which Eads had built from his own plans, and which had been with Farragut at Mobile, was bought now from a wrecking company, and her iron hull used in making the caissons; so that her usefulness still continued in peace as in war.

It has been said of Eads that he grappled with great problems in engineering, and solved them as easily as a boy subtracts two from six. While this is true, it must not be forgotten that he had not the school-training of an engineer. Nothing is more untrue than the statement that he was, like de Lesseps, only a contractor. He was a very unusually brilliant engineer, and his ignorance of the higher mathematics served to show his brilliancy the more clearly. Some persons have said that his chief talent was in explaining abstruse reasonings simply; but an engineer has told me that he thought Eads's chief talent was his ability to arrive by some rough means at a certain conclusion to a given problem, which conclusion would in every instance be approximately the same that better trained mathematicians would reach by mathematics.

By the time the bridge was finished, indeed from the time (1868) when his first report for it made a decided stir in the scientific world, both at home and abroad, Eads was a very well-known engineer. In that same year a visit to Europe for his health's sake gave him the opportunity to interview a French steel company, through whom he met a famous bridge-builder, and was led to examine the piers of the bridge then being constructed at Vichy; and it was there that he found his new ideas for caissons. Going home, by way of England, he explained his plans to the engineers there, and was by them proposed as a member of the Royal Society. Even at home, in his own adopted State, he was not without recognition; for in 1872 the University of Missouri conferred upon him the honorary degree of LL.D. From the general of engineers he received a request for suggestions for improvements in guns; and from his work on the subject of Naval Defenses it is plain that his mind still found time to run on this favorite topic.

In 1874 the bridge was finished. After it had satisfactorily stood the severe tests put upon it, it was formally opened on the 4th of July. The celebrations of that day were the first public outburst of approval given to Eads's work. And to-day the strong and graceful bridge stands as his most beautiful and lasting monument. And as even the great tornado of 1896 was unable to do the piers any serious damage, they are likely to last indefinitely, and thus make the bridge "endure," as its builder said, "as long as it is useful to man."

To Saint Louis it has been so useful that while on the one hand the growth of the city was the cause of its being built, on the other it has been one great cause of the continued growth and prosperity of the city. But it had even broader results than that. "It made a radical change in the conditions of transportation East and West, and it made possible the Memphis bridge and the future New Orleans bridge."

And in another direction yet it is peculiarly important. In bridge-building it marks an era, not only because of its strength and beauty and the daring of its design, but also because of its many labor-saving devices, the inventions of a thoroughly practical mind. A distinguished engineer calls it "a great pioneer in the art of sinking deep foundations and building spans over wide stretches of space, that astonished in its construction the entire civilized world." London "Engineering" chose it, while building, as preëminently the "most highly developed type of bridge;" and says, "In that work the alliance between the theorist and the practical man is complete." In Eads it finds its long-sighed-for dream, combining the highest powers of modern analysis with the ingenuity of the builder.

IV
THE JETTIES

The Mississippi River is a great antimonopolist. As more and more railways have been built it has been less and less used. And yet, because it drains almost every corner of a valley which comprises over one third of the whole United States, it affords means of transportation to an immense area; and since it cannot be controlled by any one company or group of companies, its freight rates can hardly be arbitrarily fixed. Still, so long as there are impediments to its free navigation in the shape of floods and bars, it cannot be depended on for shipping, and the magnificent opportunities it should offer to commerce are lessened. The vastest river system in the world, it shows in its various parts great contrasts. One large tributary flowing from the Alleghanies, one from the Rockies, one from the north, others from the southwestern plains, are each able to contribute their various products of grain, lumber, cattle, cotton, fruits, and so on. Some branches freeze every winter; others never do. Some are clear, others silt-bearing. From about Cairo it flows southward through the greater delta, or land built up by its own action in ages past, and in all this part of its course both banks and bottom are of yielding alluvion. For some hundreds of miles "the crookedest of great rivers," it varies frequently in width and velocity and is full of shoals; then for hundreds more, though uniform in width, it often rises higher than its shores, and is confined in artificial levees, which it continually breaks down. Finally, below New Orleans, growing more sluggish, and dividing into several mouths, or "passes," it wanders through tracts of waste marsh-lands into the gulf, which it colors brown for miles around. Blocking the end of each shallow mouth there was formerly a sand-bar; and these obstructions to navigation were the despair of the river commerce, and no less the despair of the government in its attempts to remove them.

Every one interested in trade or shipping realized what a very serious hindrance to the usefulness of the Mississippi these choked-up mouths were, but no one realized it better than Eads. Understanding that the great valley is capable of supporting 400,000,000 people, and intent on doing all in his power for good, even before he had completed the bridge he was studying the problem of opening the river. Its improvement and the welfare of its millions of people were cherished objects of his life. For some men one great undertaking at a time is enough, but Eads's energies were such that his works overlapped one another. It is hard to see how one man can have time, even if he has brains, to do all he did. But apparently he never lived an idle day. The bridge, with its many extraordinary solutions of new problems, made its builder's permanent reputation. At the particular request of West Point he had supplied that institution with writings, diagrams, and models. And so far afield had his fame spread that on one of his many trips abroad, he made plans, at the request of the Sultan's grand vizier, for an iron bridge over the Bosphorus. A change in viziers, however, prevented its being built.

It seems as if the river-mouth problem had not always been so difficult. Still, Eads showed that the bars were inevitable; and it is probably only because, with the growing population and trade of the central States, the need for an outlet was greater, that the problem seemed more complicated. Moreover, ocean vessels were increasing in size and draught, which also made an adequate channel more desirable. Although the blockade had forced the construction of several expensive lines of railway, yet it was impossible to carry all the products of the valley by rail. Millions of dollars' worth of merchandise were delayed at the bars. As early as 1726 attempts had been made to deepen the channels through the river's mouths by harrowing. But the first government effort was in 1837, when an appropriation was made for a survey and for dredging with buckets. Again in 1852 another appropriation was made; and a board, appointed by the War Department, recommended,—

1. Stirring up the bottom.

2. Dredging.

3. If both these methods failed, the construction of parallel jetties "five miles in length, at the mouth of the South West Pass, to be extended into the gulf annually, as experience should show to be necessary."

4. "Should it then be needed, the lateral outlets should be closed."

5. Should all these fail, a ship canal might be made.

Dredging by stirring the bottom was tried, and produced a depth of eighteen feet. Three years later this depth had entirely disappeared. In 1856 an appropriation was entered into, but the jetties were never completed. Later than that dredging was tried again. Up to 1875 more than eighteen feet of depth had never been obtained, and even that could not be steadily preserved. Channels, opened in low water, were quickly filled up with sediment in high water, and sometimes a severe storm would wash in enough sand from the gulf to undo the result of months of dredging.

As early as 1832 a ship canal near Fort Saint Philip, which should cut through the river bank out to the gulf, had been planned, and this solution had been approved of by the Louisiana legislature. That idea had been revived from time to time. And there had also more than once been new recommendations made for jetties, which by narrowing the channel should deepen it. Finally Congress ordered surveys and plans for the canal, and then appointed a board not only to report on them, but also to ascertain the feasibility of improving the channel of one of the natural outlets of the river. In 1874 this board reported in favor of the canal, and against the idea of jetties, which, in its opinion, could hardly be built, could not be maintained, and would be excessively costly.

This, then, was the situation when Eads appeared on the scene: "scratching and scraping" were going on in South West Pass, but were doing little real and no lasting good; the government engineers had declared themselves in favor of a canal; and though in some quarters jetties had been advocated, scarcely any one thought they could be built, or that if they were they would last, or that they would do any good. Eads, however, understood the river like a book, and he had studied this particular subject. He now came forward publicly, offering not only to build and to maintain jetties which would insure a twenty-eight foot channel, but to do all this for less than half the cost the board had estimated, and on a contract which should provide for his being paid only in case he succeeded. From this remarkable offer his own confidence in his plans may be inferred. A purpose which he had reasoned out as practical became an inspiration to him which nothing could shake, for his courage equaled his convictions.

But so bold was his proposition that he was considered a wild enthusiast. Never at a loss to solve any problem, again, as when he planned the bridge, he undertook to do what was commonly held to be impossible. Of course, all the backers of the canal scheme opposed him bitterly. New Orleans was of that faction. Saint Louis, on the other hand, upheld him because of his personal popularity and his signal success with the bridge. The army engineers were against him as a civil engineer. Thus the controversy was sectional, personal, and professional. Up to this time the government had invariably intrusted all works of river and harbor improvement to the military engineers; and to hand over the most important one it had ever undertaken to a private citizen, and to permit him to apply a method that had just been condemned in a report signed by six out of seven of the most distinguished army engineers, met with decided opposition. So the government hesitated. Certainly this was a proposal to make them consider, promising, as it did, an open river mouth, at a cost much lower than that of the canal, and in case of failure leaving the total loss to fall upon the contractor. Besides, several eminent civil engineers supported Eads's theory. The House, nevertheless, passed the canal bill; but the Senate, more thorough, after calling Eads and two of his principal opponents to state their views before a committee, passed a bill appointing a commission to reconsider the entire subject once more. The discussion before the Senate committee was one of the crises in Eads's life. The fate of the jetty enterprise hung on the outcome of it. Fortunately for himself and for the good of the country, he was a most magnetic and persuasive man. His theories and arguments were sound and logical, his experience of the river was vast; and beyond his aptitude for making technical reasoning simple and clear, his skill as a diplomatist was equal to his ability as an engineer.

So the commission was appointed; and, ultimately, on account of the far-reaching importance of the question of river-mouth improvement, its members decided to go to Europe to inquire into the matter. About the same time, and for the same purpose, Eads also went abroad, and while there he made a careful study of the works at the mouths of the Danube, the Rhone, and several other European rivers. What he saw there served only to strengthen his confidence in his own plans. When he returned home, there had been a noteworthy change in public sentiment. Though there still remained many either prejudiced or honest enemies to his plan, and although the newspapers were still noisy with their cheap and ignorant opposition, the country at large and Congress were inclined to accept the offer, which promised them so much at no risk at all.

The commission, returning too from Europe, where it had made as careful investigations as those of Eads, reported, by a majority of six to one, in favor of trying jetties in the South Pass. This pass, the smallest of the three mouths, had a depth of only eight feet on its bar, and had besides a shoal at its head. The South West Pass, the one which Eads had proposed to use, is not only two or three times as big, both in width and in volume of water, but it had fourteen feet on the bar, and no shoal at its head. Eads argued and implored with all his strength to be allowed to use the larger pass, as the only one adequate to the demands of commerce; and so convincing were his reasons that the House passed a bill which called for jetties in the larger pass. But the Senate, again more conservative, was cautious in this experiment, and insisted on the small pass. Finally, the bill went through, and the grant was made for the improvement of South Pass. And notwithstanding the considerable difference in size, as well as preliminary conditions altogether less promising than in the pass Eads had asked for, still, the depth of thirty feet was to be obtained,—the same result under harder circumstances. The payment promised, however, was not increased with the difficulty; but on the contrary was to be a good deal less than the estimate of the commission. The terms, which required certain specified depths and widths of channel to be obtained and then maintained during twenty years, were so arranged that Eads should not receive any part of his payment till after the work covered by that part had been finished and approved.

Hard as these conditions were, they were based on his own proposal, and he was glad even on such terms to undertake the great work he had longed to do. He at once busied himself in raising money for beginning the Jetties, and here again his peculiar talents helped him. One of his friends has said, "His powers of persuasion, his charm of address, and the magnetism of his personality opened the hearts and purses of whomever he pleaded with in support of his engineering devices. He was a most lovable man." Moreover, he was an excellent business man. He had indeed a marvelous faculty for obtaining funds with which to carry on his works; and in that time of financial distress such a faculty was very necessary.

The theory on which he based his jetties was really extremely simple. He said that, other things being equal, the amount of sediment which a river can carry is in direct proportion to its velocity. When, for any reason, the current becomes slower at any special place, it drops part of its burden of sediment at that place, and when it becomes faster again it picks up more. Now, one thing that makes a river slower is an increase of its width, because then there is more frictional surface; and contrariwise, one of the things that make it faster is a narrowing of its width. Narrow the Mississippi then, at its mouth, said Eads, and it will become swifter there, and consequently it will remove its soft bottom by picking up the sediment (of which it will then hold much more), and by carrying it out to the gulf, to be lost in deep water and swept away by currents; and thus, he said, you will have your deep channel. In other words, if you give the river some assistance by keeping its current together, it will do all the necessary labor and scour out its own bottom.

Today, since this theory has been proved, it seems as simple as A B C. And it is almost impossible to believe what opposition it then aroused. People were not only set on blocking the undertaking, but they were actually ignorant enough to deny that the velocity of water had any connection with its sediment-carrying power. Even if the narrowing process should happen to give a channel through the present bar, they said, a new one would presently form beyond, and so the jetties would have to be extended every year.