What do you notice first? The blue sky, sun-kissed figures, and vast rolling water create a sense of calm? Hopper's figures, however, are transfixed by the bell buoy, which strikes a dark note in the otherwise sunny scene. The function of a bell buoy is to issue auditory warning of submerged dangers or channel boundaries. Though the artist resisted offering explanations of his paintings, signs of impending danger here may also reference a more severe disturbance. During the time that Hopper worked on "Ground Swell," from August to September 15, 1939, World War II broke out in Europe.