In a glance, you can feel it: the scene, the mood, the forms . . . it's pure Edward Hopper. A tightly sealed atmosphere, a place forsaken by the energy of life and time; shadows cast at a long, low angle. The lone source of direct light and humanity is Jimmy's Ice Cream shop, where three diminutive figures stand inside. The twilit cityscape seems to hold no hustle and bustle; the river seems not to flow; the people seem to take no breath . . . if Jimmy were scooping ice cream, it would probably be a brand that didn't melt and drip.

But this is not a Hopper painting. It's a photograph. The 1947 painting, "Corn Belt City," was destroyed 10 years ago in a Park Avenue apartment fire.

What remains, like a next-generation image, is a black-and-white photographic negative -- one of thousands of negatives known as the Juley Collection. For almost 80 years, Peter A. Juley and his son Paul were the fine-art photographers in New York City. When, in 1975, the 85-year-old Paul Juley decided to retire, the massive accumulation of photographic negatives was boxed up and transferred to the Smithsonian's National Museum of American Art (NMAA).

A print of the "Corn Belt City" negative is on display in the museum's exhibition, "Focusing on Art: Peter A. Juley & Son," which opened last Friday and continues through May 4. For an archivist or a scholar, the Juley Collection is a full banquet (122,500 photographic negatives representing the works of more than 11,000 artists and 4,500 portrait photographs); for the browsing layman, the NMAA's understated exhibition is more of an appetizer (a core of approximately 30 Juley photographs).

"The intent [of the exhibition] was primarily to introduce the public and the research community to the Juley Collection and to indicate what it consists of," says Eleanor Fink, chief of the museum's research support office and the curator of the exhibition. "Generally speaking, photographic archives are taken for granted as mechanical throwaways, [but] they can, as the Juley Collection demonstrates, be one-of-a-kind records of lost originals."

Fine-art photography does have mechanical aspects about it. The Juleys took an objective approach -- one in which they strived to render a descriptive record of the artwork, rather than to interpret it or achieve artistic flourishes at the expense of literalism. Artist Allyn Cox, son of muralist Kenyon Cox, remembers that Peter Juley "used a thread to measure the distance from the four corners of the picture to the camera to make sure that he was exactly in the center."

The Juley photographs often provide the only extant records of particular work of arts. Like Hopper's "Corn Belt City," Robert Henri's painting of financier and presidential adviser Bernard Baruch was destroyed in a fire in 1932. William Glackens' "Lenna With Rabbits" was one of 50 paintings on an express train that derailed and burned on its way to New York in 1929.

Even a partial list of the Juleys' clients reads like an index to a book on 20th-century American art: George Inness, Winslow Homer, Thomas Eakins, Childe Hassam, Robert Henri, John Sloan, Maurice Prendergast, John Marin, Georgia O'Keeffe, Hans Hoffmann, Robert Motherwell . . .

Fink explains that "because they were the best in the business, and everybody used them, once an artist started going to the Juleys he usually remained a client" -- for life. The Juley collection not only offers comprehensive coverage of the development of American art in the 20th century, in many cases, it also documents the evolving life's work of individual artists -- "from the beginning, before the artist was perhaps well-known in the art world, to later on when, if he was fortunate enough, he was recognized by the art world," says Fink. The collection features 344 photographic negatives of works by George Bellows; 329 of sculptures by Paul Manship; and 203 of works by John Singer Sargent.

The Juley Collection provides conservators with a record of the original condition of an artwork. "If works have been damaged, or if they have suffered pigment loss, the photographs can be very helpful to restorers," says Fink.

Such is the case with the allegorical "Wind" figure of Daniel Chester French's Dupont Circle fountain. The figure's right hand was damaged and subsequently restored in the late 1930s. Additional damage has prompted another restoration project. The obvious source of information on the original appearance of the hand would have been the full-scale plaster model, which is at The Detroit Institute of Arts. But the model has lost its arms, so restorers have turned to the Juley negatives.

"By trying to find visual evidence for the second restoration and coming upon the Juley photographs, it became apparent [to art historians] that there was a discrepancy between the composition of the hand in the Juley photograph and the earlier restoration," Fink explains. In fact, the Juley photograph indicates that the original hand -- with fingers splayed and muscles charged with a taut energy -- had, under the restorer's chisel, become limp and almost indifferent to the whirling forces of wind and sea.