August 9, 1803 | Letter Thomas Jefferson to John Dickinson, August 9, 1803 Thomas Jefferson expresses his pleasure at the Louisiana Purchase, and explains the importance of the territory as a buffer against Spanish expansion.
September 21, 1803 | Letter Thomas Jefferson to William Dunbar, September 21, 1803 Thomas Jefferson questions William Dunbar about Spanish borders in the Louisiana Territory.
March 13, 1804 | Letter Thomas Jefferson to William Dunbar, March 13, 1804 Thomas Jefferson thanks William Dunbar for his letter of January 28, promising to forward his paper on the Mississippi River to the American Philosophical Society. Jefferson then writes a detailed discussion of the science of water in a river like the Mississippi. Jefferson also relates his plans for directing surveying parties to the Mississippi and Ohio Rivers, in addition to explorations of the Red and other more southern waterways. Jefferson concludes with speculations on the future of the Lousiana Territory.
April 6, 1804 | Report William Dunbar to the American Philosophical Society, via Thomas Jefferson, read April 6, 1804. The Mississippi River, its delta, and the surrounding region receive detailed attention from William Dunbar in this report forwarded to the APS by Thomas Jefferson.
May 13, 1804 | Letter William Dunbar to Thomas Jefferson, May 13, 1804 William Dunbar thanks Thomas Jefferson for his comments about Dunbar's notes on the Mississippi River. Spain's land sales in Western Florida draw the author's attention and Dunbar offers approval of continuing explorations on America's western rivers, while bemoaning Congress' reluctance to adequately fund such expeditions.