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To Thomas Jefferson from Isaac Briggs, 3 March 1806

Washington M.T. 3 of the 3 Mo 1806.

My dear Friend,

About 12 days ago, I returned from an excursion up the Mississippi river.

The object of this expedition was to ascertain, by celestial observation, the point where the Parallel of 33 degrees of north latitude intersects the western shore of the river; and also the longitude of that Point—to cause to be traced, marked and measured, as far, at Present, as the Ouachitta river the Boundary between the Territory of Orleans and of Louisiana—to make a survey of both shores of the Mississippi from the mouth of Arcansaw river down to the mouth of Chafalaya, of the Chafalaya and bayou Têche to the sea, and perhaps of the Mississippi to the Balize—and to exercise, under my immediate inspection, some young men, in making celestial observations, in order to qualify them for future expeditions of this kind.

I employed George Davis to execute this survey—his Party consisted of two assistant surveyors and two other men.

Having arrived near the 33rd degree of latitude, I sent George Davis one assistant surveyor and eight men to ascend the Mississippi to the mouth of Arcansaw—to ascertain the latitude and longitude of that Point—and to return with a survey of the Mississippi. I, with one surveyor as my assistant and two men, remained to ascertain the boundary. The latitude of the mouth of Arcansaw, very nicely taken is 33°.47’.19.5"—and I have scarcly a doubt that the boundary between the two Territories is fixed within five perches (which is less than 1") of the exact latitude 33°.

As the ground on the western side is inundated to considerable distance from the Present bank of the river, I erected on its Eastern side, on the first ground above the inundation; as a monument in the latitude of the line, a conical mound of earth, on a basis of 12 feet diameter, and planted in its centre a thrifty young sycamore tree.

As soon as I can have the necessary calculations completed I intend to report circumstantially to thee a Trigonometrical survey of about four hundred miles of the Mississippi river, checked at short intervals by celestial observation, and more accurate than could be made by tracing every foot of both shores with the compass and chain. We measured with the most scupulous exactness, every sand beach (some of them four miles in length, and few of them more than ten miles asunder) as basis of verification.

A chart made from this kind of survey from the mouth of Ohio down, will afford incalculable facility and safety to the navigation of the Mississippi by enabling boats to run during the night, for it would exhibit to them the exact shape of both shores, every shoal, and every Pass between the islands. But such a survey cannot be made with sufficient accuracy to be useful, as it must be properly checked by celestial observation and verified by frequent measured bases, for less than eight dollars per mile, which is four dollars per mile for each shore. I have made this survey so far at my own risk in hopes that Congress will sanction it by an appropriation.

The measurement of the boundary to the Ouachitta will connect William Dunbar’s observations for longitude on that river with mine on the Mississippi.

Suppose the following survey authorized, would it not be useful? To commence at the mouth of Mobille bay to ascend the bay and river and the Tombigbee river to the head of boat navigation—to Pass over to the Tennessee river, examining with a philosophic eye the ground between,—and thence down the Tennessee, Ohio, and Mississippi rivers to the mouth of Arcansaw.

Will the members of the House of Representatives recollect the compensation they intended last session for the investigation of the Post-route to New Orleans? Throught my friend William Dunbar, I last summer sent to London about seven hundred dollars for astronomical instruments, in the expectation of receiving that compensation. These instruments have been ordered to Baltimore—can they be exempted from duty?

Accept assurances of my grateful and affectionate esteem.

Isaac Briggs.

DLC: Papers of Thomas Jefferson.

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