It's all quiet on the art world front, a calm before fairs here and abroad, so The Times takes a trip to our favorite backwater no-culture town that happens to be the nation's capital, Washington, D.C., to check on how everything's going with the collection of the Corcoran Gallery. If you've plum forgotten, the Corcoran was more or less peacefully absorbed by the National Gallery, and now the remaining institution has announced the 6,500 works it's acquired for its permanent collection. Among the loot is a smattering of works by American masters, bundles of pieces by local artists, a package of a few dozen pieces by 28 black artists given by the local gallery owner Thurlow Evans Tibbs Jr., and Niagara, a painting by Frederic Edwin Church from 1857 that measures seven feet in length.