August Sander's photographs of people, conceived as parts of an encyclopedia of human types, live peculiar double lives. Each is a scientific sort of specimen, a step in Sander's visual climb up and down the social ladder, and each is a unique individual whose personality refuses to succumb entirely to the set formulas of dress, gesture and social class.

This is perhaps the main source of their cumulative power, this and the fact that together they make up an extraordinary record of the time and place most of them were taken: Germany after World War I and before Hitler. Some 250 of Sander's photographs, including landscapes and industrial views as well as plentiful selections from his unfinished opus, "Man of the Twentieth Century," are now on view at the Corcoran Gallery of Art in the exhibition, "August Sander: Photographs of an Epoch."

"Man of the Twentieth Century" is a title that doesn't exactly proclaim its insignificance. The way Sander had it worked out, it was to be a portfolio divided into about 45 sections of 12 photographs apiece, each section corresponding to a specific segment of the social order: farmers, small-town people, craftsmen, students, technicians, industrialists, soldiers, artists, gypsies and hobos, the "ill, insane, and disabled," and so on.

Sander's aim, though he probably wouldn't have put it this way, was to be a kind of Emile Zola with a camera, to construct a comprehensive picture of contemporary society, from bottom to top and back again. The project was not concluded due to the intervention of the Nazis, but one wonders whether in reality an endeavor of such scope could ever be rendered complete. As the photographs in the Corcoran exhibition demonstrate, though, the partial results are significant.

Sander was born in 1876 in a small mining village in rolling hills and woods east of Cologne. He taught himself photography; his father, a mine carpenter, helped him construct a hut that was his first darkroom. Sander made himself a success as a commercial photographer with a business mainly in portraits, and his earlier works (very few of which survive) mirror the prevailing "art" photography conventions of the time. Soft, grainy and tinted, they were made to look more or less like fine paintings.

This style didn't really suit Sander's temperament. By 1909, when he opened a studio in Cologne, he was advertising "simple, natural portraits that show the subjects in an environment corresponding to their own individuality." This wasn't too popular with the sophisticated clientele of the city, but it went over well with the humbler souls in the Westerwald, a vast wooded area southeast of Cologne, where he would bicycle to on Sundays to photograph the peasants in their church-going clothes. (Sander's change of style, basically self-motivated, coincided with similar changes from "pictorial" to "straight" photography on the part of Alfred Stieglitz and quite a few other leaders of art photography at the time.)

It was during these years that Sander first began to think about his voluminous project. Some of the photographs he took then, before he was called up for the Great War, would appear in his exhibitions during the 1920s, and they are in the Corcoran show -- serious, straightforward, self-conscious photographs, so strong in projection they might have been willed by their subjects--fine photographs in all respects save their ponderous classifications ("The Earthbound," "The Philosopher," "The Revolutionary," etc.).

Sander's best work, though, was accomplished during the 1920s. In some ways this is ironic, for in photography as in other creative fields the Weimar years were a time of fermenting experimentation and Sander literally had nothing to do with camera-less exposures (photograms), multiple exposures, light and lens distortions, photomontages -- the whole bag of tricks being explored by Laszlo Moholy-Nagy and a younger generation. But grabbing onto the hot style was not so big an issue during those years in Germany except to a few ideologues; the general level of creative excitement was so high, artists seemed to do well no matter which way they turned.

Sander did, however, share certain attitudes with Albert Renger-Patzsch and other German photographers who concentrated on crystalline images of the machine or of nature -- Sander's people are observed at a certain distance and with a certain detachment, as if they were machine parts or butterflies on a board. In part, this is precisely what they were. Sander was a student of physiognomy and followed the model of Johann Kaspar Lavater, the 18th-century Swiss pastor whose illustrated essays attempted to establish irrefutable links between facial type and individual character, except that Sander proposed to collate the indisputable linkage between physical look -- face, body, limbs, posture, gesture, dress -- and social class. He wanted to "grasp the physiognomic image of his time," he said.

The connection is commonplace -- the stock in trade of caricaturists world over and an old game everybody plays every day just walking a city street -- but to see it made in such quantity by an artist of Sander's caliber is to realize its true dimensions, for it deals with nothing less than the interdependence of society and the individual, which is to say the mystery of the human character.

Sander approached the task seriously, even nobly--anything else and it would have been a farce. As John Szarkowski, curator of photography of the Museum of Modern Art, has noted, the approach was "almost a caricature of teutonic methodology, and if it had been executed by a lesser artist, the result might well have been another dreary typological catalogue." Sander, inspired by the possibility of arriving "at a comprehensive vision of the nations of the earth in the same way that the observatories arrive at a complete image of their observed heavenly universe," was a sizably talented man.

The record he left is dated, of course, and none the worse for that. We could hardly ask for a more ambitious (though we might pine a little for a wittier) image of a given place at a given time. Costume dates all the subjects, of course, and a few of them seem like symbols -- cliche's, really -- of their time: the military student, so proud and pathetic, with a cap like an upside-down tin bowl and a face full of sword scratches; the Nazi functionary, seemingly self-satisfied; the soldiers of World Wars I and II (officer and young enlisted man being made ready for the final hopeless defense).

But even these prototypical subjects are not so simple that they fail to share something of their inner lives with the general run of humanity: they are not posters but human beings, perspicuously portrayed by an artist. Too much has been made of Sander's objectivity; he himself made too much of it. He was systematic, straightforward, and had a clear idea of what he was after, and the results were at once less and more than he expected: less in the sense that the great comprehensive goal eluded him, and more in the sense that his personal view of his society was far more vivid than cold scientific description could ever supply.

Most of Sander's landscape photographs and industrial scenes were taken during the 1930s after work on "Man of the Twentieth Century" was more or less forbidden. Some of them are beautiful, conventional romantic images of time-haunted German subjects, even though Sander said he approached these subjects with the same intentions as the portraits: to study the traces of humankind in the "physiognomy" of the earth. A few are haunted in exactly the way he intended: a brand new Autobahn, for instance, without a crowd of cars, without tanks, sweeping across a still valley.

"August Sander: Photographs of an Epoch" was organized by the Philadelphia Museum of Art, supported by a grant from the National Endowment for the Arts, and is accompanied by an amply illustrated aperture monograph with an introduction by Beaumont Newhall and an essay by Robert Kramer (125 pages, $15 paper). The exhibition continues at the Corcoran through Feb. 6.