New York may be the center of the art world, but it doesn’t have a monopoly on art, of course. In America’s other, lesser cities, there are a number of important institutions that put on shows that never reach our shores. I trekked down from civilization over the long weekend, for instance, because I wanted to see the Philadelphia Museum of Art’s Mary Cassatt at Work. The museum, after all, holds almost 10 percent of the finished works produced by Cassatt, the late 19th century, Pittsburgh-born painter. The new show—based on a two-year technical study of the Philadelphia museum’s archive but also borrowing freely from other world-class institutions—portrays Cassatt as a pragmatic, calculating, and hard-working artist, against her previous reputation as a cosseted chronicler of haute-bourgeois domesticity.