The castle-like Mercer Museum in Doylestown, Penn., which is fundraising for a $12 million expansion, offers an eyeful from its collection of paintings in the exhibit "Three Centuries of Bucks County Art and Artists." Usually held in "open storage," the seldom-seen cache now on display includes "The Peaceable Kingdom" and "Washington at the Delaware" by Edward Hicks, three works by Daniel Garber, paintings by Charles Willson Peale and Martin Johnson Heade as well as new acquisitions...