Thomas Paine: Part III

Note: read Part II.

“Whatever country I may hereafter be in, I shall always feel an honest pride at the part I have taken and acted, and a gratitude to nature and providence for putting it in my power to be of some use to mankind.” - Thomas Paine, 1783

On April 19, 1783, eight years to the day after the first battles of the war at Lexington and Concord, and the day the cessation of hostilities was publicly proclaimed to the Continental Army, Paine published the final essay of The American Crisis. Looking back over the more than seven years he had spent writing on behalf of independence, he said it was “the cause of America that made me an author,” and that whatever he had accomplished for her, he had “likewise added something to the reputation of literature, by freely and disinterestedly employing it in the great cause of mankind.”

Over the next two years, Paine became more financially secure than he had ever been. New York granted him a 277-acre farm in New Rochelle, Pennsylvania awarded him five hundred pounds, and Congress voted him three thousand dollars in 1785. While peace had left Paine without a war to write about, it did not leave him without problems that absorbed him. With this newfound financial security, Paine devoted increasing attention to an entirely different kind of problem: bridge design.

At the time, the Schuylkill River could freeze heavily during the winter as it passed Philadelphia. When the ice broke up each spring, the moving floes and the floodwaters that came with them struck anything standing in the channel, and conventional bridges built on piers were, in Paine’s own words, poorly “adapted to many of the rivers in America on account of the ice in the winter.” Piers stood directly in the ice’s path each spring thaw, and even the sturdiest were vulnerable to the damage.

Paine sought a solution. It came in the form of a bridge with no piers to catch the ice on at all. Instead, a single iron arch would cover the whole span of the river, supported by foundations built into the two banks rather than piers in the water. The bridge itself would be formed from thirteen parallel iron ribs, each assembled from curved iron bars and connecting blocks, with the ribs braced together across the width of the span.

Paine traced the principle of his idea to structures he had observed in nature. As he wrote: “The idea and construction of this arch is taken from the figure of a spider’s circular web, of which it resembles a section, and from a conviction that when nature empowered this insect to make a web she also instructed her in the strongest mechanical method of constructing it. Another idea, taken from nature in the construction of this arch, is that of increasing 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.”

In April 1787, Paine sailed for France with a model of the bridge, which he presented to the French Academy of Sciences that July. The Academy delivered a favorable report the following month. Paine then traveled to England, where he secured a patent in August 1788. An ironworks in the north of England cast and tested an experimental rib roughly ninety feet long, loading it with twice its own weight in iron to prove its strength. In 1790, a larger demonstration bridge was erected on a public green in London, where visitors paid a shilling apiece to see it.