Gifford Beal’s On the Hudson at Newburgh was hidden beneath another painting for most of the 20th century. Really. Childe Hassam once told an interviewer, “I believe the thoroughfares of the great French metropolis are not one whit more interesting than the streets of New York.” And our painting is just as good, too!, he didn’t say, but he may as well have: Upon his return from study in Paris in 1889, Hassam, along with…