The Schuylkill Permanent Bridge Company
INSPIRED BY THEIR COUNTRYMEN in Boston, a group of prominent Philadelphians undertook to solve the city’s bridge problems. In place of deteriorating and costly floating bridges, they proposed a new permanent bridge. And in place of outdated ferry leases, they sought a charter from the General Assembly, entitling them to sell shares in a new bridge company. Capital from the sale of shares would finance the construction of Philadelphia’s first permanent bridge.
The scheme was brought before the assembly in November 1786 by the Philadelphia Society for Promoting Agriculture, a new learned society founded the year before. With a membership that included Robert Morris, Benjamin Rush, Benjamin Franklin, the lawyer and jurist James Wilson, the visiting English merchant and gardener Samuel Vaughan, and George Clymer, cousin of Paine’s friend Daniel and heir to a mercantile fortune and member of Congress and the Pennsylvania General Assembly, the society asserted its considerable political and financial clout on behalf of the proposed bridge company.
By the fall of 1787, it had accumulated enough prospective investors to begin planning for the new bridge. The remaining barrier was the state government’s consent. The Agricultural Society expected the bridge to be financed by Philadelphia’s wealthiest, many of whom were its members (and also members of the state assembly), but there would be no way to pool citizens’ capital without the government’s legal sanction. By late 1787, this seemed imminent. The people’s representatives had agreed to submit a proposed Act of Incorporation for the Schuylkill Permanent Bridge Company to public review.1
The scheme was a classic public–private arrangement. After the company chose a design and built its bridge, it would charge tolls sufficient to provide investors “with legal interest, and a reasonable gratification for the risque incurred on account of said Bridge.” Once the company’s debts were paid and its shareholders compensated, the state assembly would have the power to make the bridge free to the public. To the Agricultural Society’s members, it was the most elegant solution to a pressing problem. But politics intruded. For western Pennsylvanians, the Permanent Bridge Company seemed like another Bank of North America—a boondoggle designed to enrich Philadelphia at the expense of the rest of the state. Opponents also questioned the General Assembly’s jurisdiction in the matter. There was nothing in the state constitution that gave the assembly power to negate ferry leases granted by the old colonial government or the defunct municipal corporation that had long governed Philadelphia. In chartering a new bridge company, that was exactly what the legislature would be doing.2
IN 1786, THE YEAR the Agricultural Society began campaigning for a permanent bridge, Paine was consumed with the fight over the Bank of North America. In February, he published “A Dissertation on Government; the Affairs of the Bank; and Paper Money,” followed by a series of newspaper essays defending the bank and attacking a new paper-money bill recently passed by the state assembly. Although there is no evidence that Paine was writing for hire, anonymous critics immediately questioned his motives. Just a few months earlier, in the fall of 1785, after all, Congress had paid him three thousand dollars. The attacks infuriated Paine, and may explain why he began abandoning public life for a life in architecture.
When Paine described the early genesis of his bridge in his 1803 “The Construction of Iron Bridges,” he said nothing about any controversy over the bank. His ambition was simply to devise a bridge that could endure the vagaries of the American climate: “By violence of floods and breaking up of the ice in the spring . . . bridges depending for their support from the bottom of the river are frequently carried away.” In exposing them to careening ice and floodwaters, the midriver piers on which most permanent bridges rested were the prime vulnerability of American bridges. Paine’s solution was a single arch “that might, without rendering the height inconvenient or the ascent difficult, extend at once from shore to shore, over rivers of three, four or five hundred feet and probably more.” In addition to lifting the bridge above the hazards of rushing ice and water, Paine believed his design would improve river travel by leaving “the whole passage of the river clear.”3
In order to build a practical single-arch bridge, Paine had to overturn centuries of architectural wisdom. Bridges, roofs, viaducts, arcades, and other spans were typically supported in one of two ways. They used the post-and-lintel method, with flat beams resting on columns. This was what the builders of the Charles River Bridge had done. The other method, more common in Europe, relied on semicircular masonry arches. Roman architects had discovered that the most effective means of distributing a span’s load was to direct weight outward and downward in equal measure. A stone or brick arch made from half of a circle provided the perfect ratio of lateral and vertical distribution of weight.
For Paine, this bit of ancient architectural wisdom presented a difficult problem. The height of a semicircular arch was roughly half its width. A single arch across the Schuylkill would thus be some two hundred feet tall. In order to bring traffic across such an arch, a series of enormous and cumbersome structures would have to be built. The bridge would require spandrels, structures filling the angular void between the curve of the arch and the flat road deck. These were normally built from a combination of loose aggregate fill and masonry, all adding to the weight bearing down on the arch. To bear this added weight, the arch itself would have to be stronger. Similarly, in order to bring traffic to the elevated road deck on the top of the arch, builders would have to construct embankment ramps and towers. For a two-hundred-foot arch, these would be enormous and costly. To avoid these kinds of added expenses, Old World bridge architects, with very few exceptions, relied on a sequence of small masonry arches. The Ponte Sant’Angelo, built across the Tiber in Rome during the reign of Hadrian, for example, consists of five stone arches, the longest of which is about sixty feet.4
The Westminster Bridge in London—which upon its completion in 1750 became the first masonry bridge built across the Thames since the original London Bridge was finished more than five hundred years earlier—consisted of fifteen consecutive semicircular masonry arches. This bridge illustrated precisely the kinds of problems Paine hoped his single arch would avoid. Although river ice was seldom a problem in London, bridge piers were still vulnerable.
As a tidal river, the Thames rose and fell by as much as fifteen feet during the course of a day. Any large obstructions in the river could produce furious eddies and rapids as the river water rushed in and out to sea and could even cause the river to overflow its banks. A new bridge, with a series of new piers, promised to make the problem worse. Charles Labelye, a Swiss-born mathematics instructor, military engineer, and builder of the Westminster Bridge, was the first bridge architect to attempt to address the issue. In the late 1730s, as he was finalizing designs for the Westminster Bridge, he recognized that by measuring the fall, or the difference between the water levels above and below a bridge, he could calculate the relative disruption caused by piers of varying sizes and shapes. Using this method, he also discovered that the London Bridge, long the bane of Thames riverboat men, could produce a tidal fall of as much as six feet. The massive stone piers supporting the bridge occluded nearly three-fourths of the river’s flow.
By minimizing the width of supporting piers, Labelye concluded, the fall could be reduced to as little as several inches. But narrowing the piers could be accomplished only by minimizing the size and weight of the arches above. This would, in turn, limit the size of the boats that could travel upriver, beyond the bridge. The largest of the Westminster Bridge’s fifteen arches, the central arch, was seventy-six feet in width and about thirty-eight feet high, large enough to accommodate Thames barges, but not high-masted sailing ships.
Even with Labelye’s innovations, the new piers presented problems. Somehow these masonry structures would have to be built, submerged, and fixed in place on the river’s bottom. The method Labelye settled on involved eighty-foot “caissons.” These were wooden barges upon which masonry for the piers could be set before the whole was sunk to underwater foundation pits. Labelye had calculated that this method, in the service of relatively narrow semicircular stone arches, would provide sufficient stability for the bridge. Alas, he was wrong. In late 1747, before construction of the Westminster Bridge was finished, fast-moving water had eroded the river bottom and one of the piers began to settle, damaging two adjoining arches. Similar problems persisted in the century after the bridge was completed, until finally, what remained of the whole crumbling pile was demolished in 1862.5
Paine’s solution to all of these problems came from a simple observation. For a single-arch bridge, a “small segment of a large circle was preferable to the great segment of a small circle.” Instead of building his bridge from one-half of a circle, Paine’s arch would be fashioned from a much smaller fraction of a much larger circle. With its lower arc, cumbersome and expensive spandrels and embankment ramps would be unnecessary. In effect, the load-bearing component of the bridge and the deck of the bridge could be merged into a single, elegant structure. The problem Paine faced was that this proposition flew in the face of centuries of architectural wisdom. The balance of downward and outward forces made possible by semicircular arches would have to be achieved in some new way. Paine came to believe that the answer would lie in the configuration of lighter, stronger materials.6
His conclusion came from nature, which increased “the strength of matter by dividing and combining it, and thereby causing it to act over a larger space than it would occupy in a solid state, as is seen in the quills of birds, bones of animals, reeds, canes, etc.” Each of these natural members was hollow and light, yet exhibited strength that seemed far out of proportion with its mass. The principle, Paine would repeatedly emphasize, was best expressed in “the spider’s circular web, of which [the shallow arch] resembles a section.” Like the spider’s web, Paine’s shallow arch would have strength that seemed impossible for so light a structure.7
IF PAINE’S IDEA was to be anything more than a curiosity, he would have to do what architects of buildings, ships, and other structures had done for centuries: he would have to demonstrate its validity with a precisely scaled model. But building that model would be no simple matter for Paine. Beyond his days as stay-maker, he had never really made anything. What he needed was a master model builder. Although Philadelphia abounded in skilled craftsmen, few possessed the range of abilities and the tools needed to fashion so precise and sturdy a thing as a model bridge built perfectly to scale.
Paine was fortunate to meet the very man for the job in the person of a consumptive fifty-year-old English immigrant. John Hall had arrived in Philadelphia in August 1785, leaving behind a family farm and gristmill in Leicester, not far from the booming industrial town of Birmingham. Hall came to America intending to buy land and resume his former trade as small farmer and miller. But he needed temporary employment before establishing himself in the countryside. Through mutual friends, Hall and Paine met in November, and within weeks Hall had begun working for Paine on a thirteen-foot wooden model of a bridge. Before immigrating, Hall had led the life of a country miller, but he was remarkably learned. “Asthmatic” episodes, fevers, and bouts of nausea, all caused by his tuberculosis, fed an obsession with medical science. The mechanics of maintaining his family’s gristmill fed his fascination with nature’s mysteries. He studied the writings of Isaac Newton and countless other natural philosophers. He also read such well-known political philosophers as Thomas Hobbes and the French Baron de Montesquieu. He owned a collection of deist tracts and books by such British radicals as Richard Price, the Unitarian opponent of the American War.8
But what made Hall so valuable to Paine was less his taste for medicine, science, and philosophy, or his progressive religious interests, than his equally well-cultivated comprehension of the mechanical arts. Before coming to America, Hall had been a maker of things. When not tending his Midlands gristmill, he spent his days and nights fashioning what was essentially miniature furniture. From walnut, mahogany, and other hardwoods, he made delicate boxes with intricate inner compartments and drawers, small precise hinges, locks, and keyholes. His customers purchased these to hold mechanical tools, scientific instruments, books, jewelry, glassware, guns, personal papers, and other valuables. In the parlance of nearby Birmingham, Hall had been what was known as a “toy-maker.” Such a person did not make toys for children, but instead made small trinkets, including buttons, shoe buckles, sword hilts, watch chains, candlesticks, and the kinds of delicate small objects Hall made. So well-known had the Birmingham area become for its toy-making that in a 1777 address to Parliament, Edmund Burke called it the “toy-shop of Europe.”9
The city’s best-known toy-maker was Matthew Boulton, who, in partnership with the Scot James Watt, became Great Britain’s foremost manufacturer of steam engines. Boulton and Watt were also part of an extraordinary learned society that arose in Birmingham. The Lunar Society attracted the region’s most inventive minds, including Erasmus Darwin, the physician (and grandfather of Charles); Joseph Priestley, the freethinking chemist and champion of American independence; the potter Josiah Wedgwood, father of British mass production; and of course Boulton and Watt, whose steam engines revolutionized the British iron and coal industries.
FOR MOST OF HIS ADULT LIFE, Hall had spent his time making boxes, reading books, and tending his mill. In America, he broadened his horizons. When not crippled by tubercular fits, he spent his days studying the workings of his new country. Hall sat in the gallery of the Pennsylvania Statehouse observing court proceedings and assembly debates. He discoursed with his new American friends about the nature of law, government, and the mechanical trades. He trolled the streets of Philadelphia studying the terms of trade and business, recording the peculiar habits of the Americans. And what he found, he quite liked.
The United States “is the best Industrious mans Country Known,” he explained to his nephew Joseph, because here, one’s skills and one’s labor were truly one’s own. “A Prudent Industrious Farmer may live well and Comfortably and have neither the fear of a frowning Land lord nor the fruits of his Industry Stolen from him by the proud & Imperious priest,” he noted. But what really made America so remarkable was its people’s unmistakably democratic ways: “You may as well Expect Grapes to Grow on thorns as to hear them Say master or Mistress[.] No those words wd Choke them.” Everyone in America, or at least in Philadelphia, it seemed, was treated equally.10
Hall’s relationship with Paine echoed these American ways. Although Paine was the architect and Hall the model builder, the two were fundamentally collaborators. Hall discussed design decisions with Paine, and Paine assisted Hall with the model building. The collaborators also shared the duties of interpreting their models to an interested public. Here too, the democratic principles Hall so admired would govern the process of design and invention. What made models so effective was the universality of the language they spoke. Any reasonable, sensitive viewer could judge a model’s beauty and integrity. This was particularly true of Paine’s thirteen-foot bridge, since anyone could test the design simply by walking across it.