A Review of "John Constable In the catalog foreword for "John Constable: Oil Sketches From the Victoria and Albert Museum," an unnamed 19th-century commentator is quoted describing the landscape sketches of Constable as "Nature caught in the very act." In the very act of what? That is the kind of remark that turns benign-looking clouds, trees and seascapes into ... well, something else. You wonder if you're missing something. And you probably are. But nothing is lurking amid the trees and cottages and views of sunsets. Instead, it is that subjects and techniques that once seemed daring and off-limits have been assimilated so completely that they have become commonplace. Such is the case with Constable's sketches. And so, as James Steward, director of the Princeton University Art Museum, said in an interview, the current show is an attempt to "re-radicalize" Constable for 21st-century viewers. What do we need to learn - or unlearn - about early-19th-century painting to view Constable as radical? The most important thing is that he specialized in landscape. For a student trained in the British Royal Academy at the turn of the 18th century, landscape was lower in the hierarchy of genres than biblical and historical subjects. Constable was also drawn to local landscapes rather than classic Mediterranean ones, and rather than transforming these into grand mythologies or allegories, he painted them using scientific methods of observation drawn from new fields like meteorology. Books like Thomas Forster's "Researches About Atmospheric Phaenomena" (1815), a copy of which Constable owned, are on view alongside the sketches. Perhaps most important, however, is that Constable painted his sketches outdoors, en plein air. The earliest works in the exhibition, which occupies two rooms and includes 85 paintings, oil sketches, watercolors and drawings, are rather placid and staid, but they are also designated as the "Apprenticeship" years, from 1800 to 1809. During this time, Constable was a student at the Royal Academy and then lived back at his parents" home in Suffolk. His father was a successful merchant who owned flour mills, river barges, a wharf and a ship that transported the flour to London. He was also under the influence of earlier landscape specialists like Claude Lorrain and Jacob van Ruisdael - but unlike those artists, he made a regular practice of painting outdoors, taking pieces of canvas and tacking them to the inside lid of his paint box. The pinholes in the top of "Dedham Vale: Evening" (1802), which depicts a sunset over gently rolling hills, are evidence of this. What is striking about the subsequent decade is how Constable used oil sketches to record nuanced effects of light and changes in the weather - an approach that would profoundly influence later artists, like the French Impressionists. Sketches done in Hampstead, at that time still a rural village just outside London, show light piercing the atmosphere or storm clouds gathering. "Landscape With a Double Rainbow" (1812), which is dominated by a deep blue sky, depicts a phenomenon not fully understood in the early 19th century, but discussed at some length by the artist in the second edition of his illustrated book "English Landscape Scenery" in 1833. What also becomes obvious, particularly when you encounter the larger sketches for exhibition paintings, is how "finished" these canvases look to us now. This is very much because of the Impressionists, who were rejected by contemporary critics and audiences because their canvases, composed of quick, broken brush strokes, looked too much like sketches compared with the slick, varnished canvases of their academic peers. Full-scale, six-foot-wide sketches here, including studies for famous works like "The Hay Wain" (1821) and "The Leaping Horse" (1825), are composed of quick brush strokes and dabs of white paint that brighten the paintings; they also have a freshness and immediacy that postmodern viewers appreciate, since it emphasizes the process of the painter and the "performance" of painting more than the finished product. In Constable's day, the French were already impressed by his landscapes. The completed version of "The Hay Wain" (1821), which features a horse-drawn cart standing in water in a verdant landscape, didn't attract much attention when it was shown at the Royal Academy in London in 1821. At the Paris Salon of 1824, however, Constable earned a gold medal when he exhibited it alongside his other paintings. The catalog describes the reaction of French artists like Théodore Géricault, said to have been "quite stunned by it," and Eugène Delacroix, who reportedly touched up one of his own paintings after viewing the pure color of "The Hay Wain." Delacroix later owned one of Constable's sketchbooks, done in Brighton in 1824. In a conversation in the galleries, Mr. Steward said he considered putting on the wall a quotation from Sir Kenneth Clark, the British art historian, who declared that the two full-size sketches for "The Hay Wain" and "The Leaping Horse" were "perhaps the greatest pictures ever painted in England." This, of course, would challenge the beliefs of 19th-century critics like John Ruskin, who championed J. M. W. Turner. But showing Constable as an artist's artist is more effective than merely showing him as a great one; the fact that we have to be re-educated to see his sketches as radical, when their techniques and processes have been so thoroughly assimilated into mainstream Western art, seems evidence enough that he was accepted, even during his lifetime, by his peers. "John Constable: Oil Sketches From the Victoria and Albert Museum," Princeton University Art Museum, through June 10. Information: (609) 258-3788 or princetonartmuseum.org.