“WINSLOW HOMER loved a good repoussoir: Locking the foreground and background into a taut tug-of-war charged his small paintings with titanic vigor. Rocks, waves, boats, and leaping fish bound toward the viewer, while some kind of natural force draws the eye back into the painting. That push-and-pull is emotional as well as compositional: We do not know whether to sympathize with or ridicule his subjects.”