An excerpt from Erica Wagner's Chief Engineer
The astonishing story hidden in the towers of the Brooklyn Bridge
The Brooklyn Bridge has been in the news — two cadets were killed, and many people injured, when a Mexican naval vessel crashed into the bridge on Saturday May 17. The bridge itself, which opened to the public just over 140 years ago, was undamaged; but when work began in 1869 many thought its completion was uncertain or even impossible, for nothing like it had ever been built before. Its construction was fraught with danger, as the following narrative demonstrates. It was also in mid-May that the foundations of the bridge reached their final — and at the time, extraordinary — depth. The ‘caissons’ of the Brooklyn Bridge were chambers deep beneath the river’s surface: it was a brand-new, dangerous technology. As the tower climbed, the caisson sank, the riverbed dug out by men working in compressed air. At the time the effects of compressed air on the body were not understood. Washington Roebling himself, along with many of his men, was badly affected by the condition. Next time you cross the Brooklyn Bridge, consider the remarkable decision made by a single man on a single day in May.
The first real caisson was constructed in a coal mine in the Loire Valley by Charles-Jean Triger; and here, in 1840, the first medical observation of “the bends” — so called because of the twisting agony it caused in its victims — were made. Two physicians, B. Pol and T. J. J. Watelle, noted the “severe pains in the arms and knees” suffered by some of the men; they would also observe that On ne paie qu’en sortent, “one only pays on leaving”. It wasn’t being down in the caisson which caused the problem: it was coming back up into normal atmosphere. They were also the first to suggest that a return to the compressed air would effect a cure. Decades later, in Brooklyn and New York, Washington too would note that this “heroic mode” of returning straight down into the pressure would alleviate the “intense pain” the condition caused. “The fact remains, however, that the effects of compressed air on the human system constitute the principal difficulty attending deep pneumatic foundations,” he wrote in 1872.
Andrew H. Smith, a physician hired by Washington Roebling to look after the men working down below, had been carefully observant of the strange effects of the disease: pallor of the skin, caused, he surmised, by decreased circulation to the surface of the body; for the same reason the fingertips would appear shrunken, as if the hands had been soaked in water. The men suffered pain as if they had been “struck by a bullet”; “as if the flesh were being torn from the bones”. Washington had written in his notes for the caissons that everything must be built “strong enough for a pressure resulting from a depth of 100’, to which it may be necessary to go.” In late April a German called John Myers died; and then a 50-year-old Irishman, Patrick McKay, after he was found “sitting with his back against the wall of the lock, quite insensible.” Washington would note that while the deaths were regrettable, “the number has been much less in proportion to the number of men employed than upon any similar work”.
It’s not hard to understand why that “heroic mode” was so infrequently applied: relief from pressure, rather than the pressure itself, is the cause of the problem, which seems counter-intuitive. Anyone would have wanted to flee from the strange atmosphere far below the river. Smith did not understand the true cause of the caisson sickness afflicting the workmen. At high pressure, nitrogen in the atmosphere saturates the blood and fatty tissue of the body; if decompression is too swift, these stores of nitrogen are quickly released, forming bubbles in the blood that coalesce in the venous bloodstream, blocking the flow of blood and causing terrible pain or worse, depending on where the blockages occur. French physiologist Paul Bert had begun to understand this at just the time Smith was considering the problem — and was the first to describe the real cause of decompression sickness — but Smith disagreed with Bert explicitly. Smith believed, as many at the time did, that the problem was caused by too much time spent inside the caisson, and that longer should be spent “locking out” — he was right about that, but for the wrong reason. He advised 5 minutes per atmosphere, or for every 14.7 pounds of pressure added; even that was hard to get the men to adhere to, and it bears no relation to the times advised for decompression in modern diving tables.
That spring the city’s papers kept the public informed about the cost of the work to men in the caisson. Eugene Sullivan, of 23 Roosevelt Street, and Louis Gifford, of 25 Baxter Street, were taken “suddenly ill” on April 30, 1872, according to the New York Herald; Michael McGuire and Dominick Montrass were both “seized with sudden illness” according to the New York Times on May 5th. In the same week the men went out on strike after higher pay for what had become dangerous work; on May 10th the Bridge Company agreed to pay $2.75 for a four-hour shift.
But on April 26 the Herald had run a short article authored by Francis Collingwood, Washington’s able lieutenant. “The pleasant task devolves to me to announce to you that we have this afternoon uncovered the bedrock under the New York caisson,” he wrote. At 70 feet Washington had ordered that soundings for bedrock begin — and at 75 feet “sharp, thin ridges” of Manhattan’s gneiss were discovered. The bedrock wasn’t level — but Washington’s knowledge not only of engineering but of geology too, meant that it didn’t need to be. There was no cause to keep digging, and risk the lives of more and more men, in order to lay the final foundation for the New York tower. “No part of its surface shows the rounding action of water or ice,” he wrote of these spurs of bedrock in his official report, showing they had never been affected by erosion or movement. They were covered with “a very compact material, so hard that it was next to impossible to drive in an iron rod without battering it to pieces”. And so, the caisson could come to rest. “On such a bottom no sliding can ever take place, no matter what the average slope might be,” he wrote. This surface “was good enough to found upon, or at any rate nearly as good as any concrete that could be put in place of it... It was determined to rest the caisson on this material at a depth of seventy-eight feet.” The New York tower of the Brooklyn Bridge, in other words, would rest on sand. Extremely compacted sand, but sand, nonetheless. And so it does to this day.
In the archives at Rensselaer Polytechnic Institute —Roebling’s alma mater and where most of the Brooklyn Bridge papers reside — there is a small collection of Roebling “artefacts”, as they’re called in the catalogue. They’re noted at the end of the listing, after all the series and subseries which make up the university’s holdings, from John Roebling’s “cholera expenses” from 1854, to Washington’s copy of G. P. Quackenbos’ “An English Grammar”, published in 1862. There are not many objects: the doorknobs and doorknockers from Washington and Emily’s house on Columbia Heights, now long-demolished; the marble bust of John Roebling that presides, somewhat eerily, over the library’s Fixman Room.
One of these artefacts is a small stone: not quite two inches long, perhaps an inch wide. It doesn’t look like anything special. It is labelled, with a piece of tissue carefully cut to fit its shape. On the tissue Washington has written in his careful hand: “Gneiss from the Bed Rock under N. Y. Tower East River Bridge 1872 79 feet below H. W.”
It is very unlikely that he collected this stone with his own hands. For by now Washington himself was badly affected by his constant trips from Brooklyn to the construction site, by the pressure, by the strain of the work. As he would write coolly in the report on the construction delivered in June 1872, “considerable risk and some degree of uncertainty was necessarily involved” in the construction of the towers’ foundations. “At the commencement of this enterprise, they constituted the principal engineering problem to be overcome, and not until they were accomplished facts could it be said that the project of the bridge was placed upon a firm, immovable footing. The subsequent building of the Towers and of the superstructure is all work which has been done before on a smaller scale. But upon the Tower Foundations rests the stability of the entire work. The whole enterprise depended on their success.”
Perhaps it was Francis Collingwood — three years older than Washington, who had started his career in the family jewellery business in Elmira, New York, before being drawn back into the work he’d trained for at RPI — who brought Washington this simple treasure. Also at the library at RPI there is a long document in the sloping, confident hand of Emily Roebling — the chief engineer’s brilliant wife would become essential to the work as time went on. “The period of time at the end of the sinking of the New York caisson was one of intense anxiety for Col. Roebling,” she wrote in a portrait of her husband; this unremarkable stone offers a physical marker of relief. Washington Roebling was a thoughtful man, and a sensitive man; but he was not a sentimental man. He was not a man for keepsakes, although he would, in later life, carefully preserve the public record of his and his family’s lives. This stone, however, he kept.
The digging stopped on May 18, 1872. It was a cloudy day, according to The New York Times, which also printed on that day an exchange of letters between President Ulysses S. Grant and former Confederate general Robert E. Lee. Grant assured Lee that “this application of Gen. R. E. Lee for amnesty and pardon may be granted to him”; a few days later Grant would sign the Amnesty Act, lifting voting and office-holding restrictions on most former members of the Confederacy. Only now was the terrible war coming to its close, those who’d fought in it might think; rebuilding a country meant building bridges where before there had been none. And here in New York and Brooklyn there would, at last, be a bridge that would be, in its own way, a symbol of that reconstruction.
Chief Engineer: Washington Roebling, the Man Who Built the Brooklyn Bridge, is published by Bloomsbury