ON THE CONSTRUCTION OF IRON BRIDGES. AS bridges, and the method of constructing them, are becoming objects of great importance throughout the United States, and as there are at this time proposals for a bridge over the Delaware, and also a bridge beginning to be erected over the Schuylkill at Philadelphia, I present the public with some account of the construction of iron bridges. The following memoir on that subject, written last winter at the federal city, was intended to be presented to con But as the session would necessarily be short, and as several of its members would be replaced by new elections at the ensuing session, it was judged better to let it lie over. In the mean time, on account of the bridges now in contemplation, or began, I give the memoir the opportunity of appearing before the public and the persons concerned in those works. Bordentown, New-Jersey, June, 1803. THOMAS PÄINE. TO THE CONGRESS OF THE UNITED STATES. I HAVE deposited in the office of the secretary of state, and under the care of the patent office, two models of iron bridges; the one in paste-board, the other cast in metal. As they will show by inspection the manner of constructing iron bridges, I shall not take up the time of congress with a description of them. My intention in presenting this memoir to congress, is to put the country in possession of the means and of the right of making use of the construction freely; asI do not intend to take any patent right for it. As America abounds in rivers that interrupt the land communication, and as by violence of floods, and the breaking up of the ice in the spring, the bridges depending for support from the bottom of the river, are frequently carried away, I turned my attention, after the the revolutionary war was over, to find a method of constructing an 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. The principle I took to begin with, and work upon, was that the small segment of a large circle was preferable to the great segment of a small circle. The appearance of such arches and the manner of forming and putting the parts together admit of many varieties, but the principle will be the same in all. The bridge architects that I conversed with in England denied the principle, but it was generally supported by mathematicians, and experiment has now established the fact. In 1786, I made three models, partly at Philadelphia. but mostly at Bordentown in the state of New-Jersey. One model was in wood, one in cast iron, and one in wrought iron connected with blocks of wood, representing cast iron blocks, but all on the same principle, that of the small segment of a large circle. I took the last mentioned one with me to France in 1787, and presented it to the academy of sciences at Paris for their opinion of it. The academy appointed a committee of three of their own body-Mons. Le Roy, the abbe Bossou, and Mons. Borda. The first was an acquaintance of Dr. Franklin, and of Mr. Jefferson, then minister at Paris. The two others were celebrated as mathematicians. I presented it as a model for a bridge of a single arch of 400 feet span over the river Schuylkill at Philadelphia. The committee brought in a report which the academy adopted that an arch on the principle and construction of the model, in their opinion, might be extended 400 feet, the extent proposed. In September of the same year, I sent the model to Sir Joseph Banks, president of the Royal Society in England, and soon after went there myself. In order to ascertain the truth of the principle on a larger scale, than could be shown by a portable model of five or six feet in length, I went to the iron foundery of Messrs. Walkers, at Rotherham, county of Yorkshire, in England, and had a complete rib of 90 feet span and 5 feet of height from the cord line to the centre of the arch, manufactured and erected. It was a segment of a circle of 410 feet diameter; and until this was done, no experiment |