John Updike asked the crucial question: When we talk about landscape painting, why do we hear of the American Sublime but never, say, of the French or Chinese Sublime? Keep that thought in mind at the exhilarating dual exhibition of 19th-century American landscapes opening today at the National Academy Museum.

Eighteen of Frederic Edwin Church’s own works from Olana, his 250-acre estate in Hudson, N.Y., are on your doorstep.This is the first time they have moved as a group from the artist’s Persianesque villa. There is real advantage in seeing them at the National Academy Museum. Here, they breathe better on their own as paintings, unconfined by their role at Olana as accoutrements to one man’s Arabian Nights.

Another 18 Hudson River School paintings come from a recent exhibition at the New Britain Museum, where this private collection went public for the first time. Included are works by Thomas Cole – the premier painter of the school – Albert Bierstadt, Asher Durand, Martin Johnson Heade, and, among others, John Kensett, laureate of Lake George. Having both collections together is a rare event, and a homecoming. These painters exhibited at the National Academy of Design when it was the essential route to acceptance in New York.

Every work on view is forthcoming, evidence of the role art played in reinforcing the young country’s image of itself. Lovers of pure painting will find much gratification here, as will anyone interested in the making of the American mind in its decades of emergence from colonial roots.

It was 1845. James Fenimore Cooper’s tales of the displacement of “heroic savagery by heroic civilization” were a household staple. The Democratic Party’s platform called for “reoccupation of Oregon, re-annexation of Texas.” The slogan “Fiftyfour forty or fight” was in the air (54- 40′ N was the latitude to which expansionists claimed title). President Polk was anticipating a fight with Mexico over California, and fearful that England or France would endanger us by getting it first. The transcontinental railroad was still only a proposal, recently dropped on congressional desks.

In that same year, the young Church (1826-1900) painted “The Catskill Creek” under the tutelage of Thomas Cole, who elevated landscape painting to a national art form. Summoned with lively honesty, the immediate locale fills the foreground. Light skips across foliage and illuminates a distant barn, carrying your attention past the creek to the movement of the sky reflected in it. Clouds follow the light, moving west into the vast spaces beyond the profile of Kaaterskill High Peak. It is just this progression, combined with Church’s preternatural gift for atmospheric effects, that developed into celestial portrayals of providential import. What began as bucolic scenery evolved into an anthem for New World destiny.

Cole instructed his protege “to paint things as you see them.” But Church saw landscape with the mind’s eye as well, and drenched it in meaning derived from his New England Calvinist heritage. The ecstatic Puritan vision of America as the City on a Hill – the New Jerusalem provided by divine discretion for a fresh initiative – finds expression in Church’s spellbinding skies. The incandescent heavens of “Sunset” (1856-65) and “Twilight, a Sketch” (1858) ignite over a continent to which providence had been so generous. Our embattled term “under God” was first phrased in paint 50 years before the pledge of allegiance was written.

Church’s “Niagara” (now at the Corcoran) was the sensation of 1857. Panoramic formats were in vogue, and the painting unrolled by the yard. On view at NAM are smaller but still stunning treatments: “Horseshoe Falls” (1856-57) and “Study for ‘Under Niagara’ ” (c. 1858). Pristine, powerful, and abundant, the falls and their rebounding mists convey the energy of the world starting up again in the hands of the American Adam. Here, as throughout the entire exhibition, you encounter the era’s recognition that landscape painting was the matchless expression of American vitality.

The Civil War shattered Adamic ideals, and Darwin’s “The Origin of Species” further eroded faith in America’s ordained role as a favored nation. But Church’s piety found equal outlet in other zones and climates. Despite the undisputed majesty of his American landscapes, Church’s most acclaimed paintings were of equatorial South America. In 1859, his 10-foot “Heart of the Andes” drew 500 paying spectators daily at New York’s 10th Street Studio Building. All the essentials of that work are here in his earlier study for it.

Sorcery is everywhere on view, but I took particular delight in Louis Mignot’s Dutch-inspired “Snow Scene” (1856). It depicts New York State in the last throes of the Little Ice Age, whose bitter effects lasted into the 1850s. (Current dismay over global warming is a luxury of central heating: Church wintered in Mexico to escape harsh freezes in the Hudson Valley.) Poise and austerity mark Martin Johnson Heade’s treatment of the meadows, mudflats, and salt marshes of coastal wetlands, beautifully summarized in “Lynn Meadow, Mass.” (1871-75). The gathering storm of Asher B. Durand’s persuasive “View of the Shandaken Mountains” (1853) is the work of a man who revered what he looked at. But it is hard to know from Bierstadt’s small panel “Sunset Over the River” (1868) that Bierstadt was Church’s main competitor for panoramic splendor, or the only Hudson River School painter who sought natural spectacle across Wyoming and into the Rockies.

My single regret is that none of Church’s remarkable North Atlantic works are here. Studied onsite near the Arctic Circle, his luminous icebergs represent what was, by the end of his career, the last emblem of the Sublime.

Until April 30 (1083 Fifth Avenue, 212-369-4880).