Poplar Forest near Lynchburg Aug. 2. 19.
The subject of the bridge, on which you are pleased to consult me, is one to which I have paid too little attention to answer usefully. I am sorry therefore I cannot improve the opportunity you give me of rendering a service the person for whom I think you can have the soundest advice is Thomas Moore, now employed as the engineer of the state. his causeway across an arm of the [. . .] island is an example of the powers of original mind in availed itself of the resources of our own country, instead of the Common place & expensive processes of Europe, which require a public treasury to supply them. while the government removed at Philadelphia, and was employed in planning the present capitol Genl Washington desired me to lay it before the ablest architects of that place for observation. I did so; and I remember one fact which may be useful to you. they all concurred in saying that it was settled by experience that 40.f. was the greatest length to which any beam of timber could be trusted, without intermediate support. this gives the law to the distance between pier and pier. I am about building a bridge over the Rivanna, and of all govern myself by it. I shall make my piers parallelogram running with the of the stream, but pointed above, instead of being square and with a cut-water beam projecting up-stream to break the ice and give a safe direction to floating . I think to make the piers of common stone with a fair face, and then to coat them with sawed logs, dove tailed at the corners, & fortified at the dove tails with broad & then iron bars. the coat will protect the stones from being justled from their places, by floating timber, and when the logs rot they can be taken away, and replaced without disturbing the wall of the pier. these are trifles and are offered merely in proof of my respect for your request and of my readiness to do more were it in my power. accept them therefore merely as manifestations of my high respect and esteem.
DLC: Papers of Thomas Jefferson.