Each year between 1819 and 1825, English painter John Constable (1776-1837) submitted a monumental canvas to the Royal Academy of Arts in London for display in the Summer Exhibition. These so-called "six-footers" captured the life of the River Stour in Suffolk, where Constable grew up and where he returned to paint each summer. "The Leaping Horse," the last of these canvases, now a major work in the Academy's permanent collection, is the subject...