“My work embodies little visions of the great intangible,” said Marsden Hartley, hailed by many as “America’s first great modern painter of the 20th century.” Vibrant colors, voluptuous forms, and bold lines are a hallmark of his work, which has something of Walt Whitman’s empathetic embrace of man and nature. This is Europe’s first major retrospective of Hartley in over 60 years. —E.C.