I have had the honor of receiving your letter of the 28th. March accompanied by the printed account of discoveries on the Missouri &c which I have read with particular satisfaction. Mr Freeman with his party left this place the 28th April for the Red River, very commodiously fitted out with Lieut. Humphrey as geographical assistant, he is a young Officer of considerable talents: Lieut. Gaines having at last declined going, it was fortunate that we met with Mr. Humphrey who bears an excellent character in every respect; Mr. Freeman and he seem already particularly attached. we are in hopes that both he & Mr. Custis will be able to take celestial altitudes so as to form a Complete set of observers with Mr. Freeman.

In consequence of the permission given by your orders & instructions to the Conductor of the Party, I have taken the liberty of adding a few hints derived from my own experience, which may be useful to the Gentlemen.

Mr. Briggs’ measurement across between the Mississippi and Washita makes a very material change in the relative position of the two rivers, this appears to be 50 miles. His observations for the Longitude (he informs me) will remove Mr. Ellicots Mississippi farther East, but he has not completed his Calculations.

The Mississippi is so remarkably low this Season, as not to flow into the bayous or outlets which are generally brim-full at this time, the Atchafalaya which is always open is probably the only small outlet which derives any water from the Mississippi; altho this is not unfavorable for operations by Chain & Compass &c yet it does not admit of that facility of transport favorable to my views in ascertaining the position of points of the Alluvial Country by astronomical observation; I cannot therefore take advantage of your indulgence for this Season; next year may prove more favorable & may not probably be too late.

Mr. Briggs is much gratified by the communication which I made him.

I have the honor to be with perfect respect and attachment Your most Obedient Servant