As we get ready to celebrate the 250 th anniversary of the nation’s founding—in an America stressed by authoritarian overreach, economic anxiety, and partisan trench warfare—we might look back for a lesson or two to 1876, when the United States threw itself its most lavish birthday party, on its Centennial.  For six months, Philadelphia’s Fairmount Park hosted the continent’s first World’s Fair , a triumphal extravaganza that comprised some 200 buildings including spectacular glass palaces that highlighted the inventions, manufactures, and arts of America and the world.  Visitors marveled at giant locomotives, vast arrays of pumps and drills, the first typewriters, an electro-magnetic mallet that could be used either to fill teeth or as a pen, the “Difference Engine” (an ancestor of the computer) which performed up to 20 complex calculations per minute, one of the greatest exhibitions of American art to date, alongside potent patriotic relics such as George Washington’s buckskin breeches and the…