1From Thomas Jefferson to Thomas Walker and Daniel Smith, 29 January 1780 (Jefferson Papers)
As we propose this Spring to take possession of and fortify some post as near the mouth of Ohio as the ground will admit, it becomes very important for us to know the exact latitude thereabouts. I take it for granted that your present Line will be stopped before you get there by unpurchased Lands. We therefore wish extremely that one of you would take a trip to the mouth of the Ohio with your...