Bouncing down an empty country road, past browning cotton fields lined with signs advertising church services and cheap guns, historian John A. Lupton hunches over a minivan's steering wheel and ignores his aching back.

He has been traveling for six days -- covering five states and more than 1,400 miles -- in a mentally exhilarating and physically exhausting pursuit of anything handwritten by Abraham Lincoln, as well as documents addressed to him: a frayed envelope the president addressed to a Confederate sympathizer; a dirty sheet of paper filled with the grumblings of a cotton farmer; a faded journal entry with notes about property rights that Lincoln scrawled in the margins.

It's been a good trip so far. Lupton and his colleague Erika Nunamaker have tracked down 33 documents.

Over the last seven years, more than 11,000 pieces of paper with Lincoln's elegant script -- and nearly 28,000 documents addressed to him -- have been found. After the pair scan the papers onto their laptops, they return the originals to their owners, and move on to find the next yellowing scrap.

Lupton thinks there are tens of thousands of papers left to discover. Maybe more.