Th: Jefferson presents his salutations to M. Tardieu, and his thanks for his excellent maps of the United States & the bay of Mexico. he incloses for his acceptance an actual survey of the Missisipi from it’s source to the mouth of Ohio. this was done by ascending the river with a compas, & long line, & correcting the latitudes from time to time by celestial observations. it is undoubtedly more accurate in it’s details & latitudes than any delineation of that part of the river which we have had heretofore. it is to be regretted that the magnetic courses were not corrected by observations of longitude also.   Governor Lewis, who conducted the exploring journey to the South sea, will give us a map of Louisiana, in which the Missouri & Columbia will be laid down with the most perfect accuracy, & the rest of that country from the best sources of information as yet possessed. Th:J. will have the pleasure of sending a copy to M. Tardieu, as soon as it appears, & has that at present of assuring him of his respect.