Imagine holding Thomas Jefferson’s letters, a book printed by Paul Revere, an original lottery ticket signed by John Hancock himself. New England is home to some of the country’s oldest antique treasures, and as book lovers descended on Boston this weekend for the International Antiquarian Book Fair, Callie Crossley delved into what makes these rare old books special and valued with Ken Gloss, of Brattle Book Shop in Boston, and Seth Kaller, a New York-based dealer of historical documents, letters, and autographs.