Three exceedingly rare 19th century U.S. currency notes are expected to sell for a combined $7 million when they are auctioned off next week. One of the unique bills being auctioned is a $1,000 "Rainbow" note from 1869 that's said to be the only one of its kind in private hands, according to Stack's Bowers Galleries. It was last auctioned in 1946 and features a portrait of DeWitt Clinton, who oversaw the construction of the Erie Canal during his tenure as the sixth governor of New York. The auction includes another "Rainbow" note in the $500 denomination that depicts President John...