Logic tells that all decades last exactly 10 years, knowledge teaches that history seldom fits as neatly as we pretend into decadal categories -- the Twenties, the Sixties, the Eighties -- and wisdom preaches that, in any case, such divisions count for little in the sweep of time.

Occasionally, however, we are permitted to suspend belief. The exhibition currently on view at the Octagon Museum, "Palaces of Dreams: The Movie Theatres of John Eberson," provides such an opportunity. Though the story it tells is reasonably familiar, the show is nonetheless a treat. It's compact, digestible and focused on a single architectural element, the movie palace, that pretty much had a beginning and an end in the 1920s and that sums up the decade's uniqueness and its logic-defying brevity.

Eberson (1875-1954), one of a handful of architects of his generation who specialized in movie houses, designed his first "atmospheric" palace for Houston in 1923 and his last for the Bronx in 1929. To emphasize its irony one is tempted to place the word "palace" within quotation marks, except that the modifier "movie" does the job. Together the words fit so strangely yet precisely: What sensational, oddly sensible things they were, these movie palaces, and how particular to the economics, the technology, the urban milieu and the social mores of their now-faraway time.

Size was important, as it often is in America: No self-respecting palace offered fewer than a thousand seats, and many doubled or tripled that. Nor was size figured alone by seating capacity; the auditorium itself often was only the half of it. Entryways were big and lobbies vast, to accommodate intermission crowds. Even the "Men's Smoking Room" and "Ladies' Parlor" with "Cosmetic Room" were spacious and very, very swell.

Pretension, but of course, was another key element, and one that separates the fantasy palaces of the '20s from the big but (usually) simpler movie theaters that came later from the office of Eberson, and others. It was pretension of a canny sort. Gobs of money were spent on statues, fountains, bas-reliefs, finials, murals, urns, sconces, lamp stands, medallions, carpets, grilles, columns, balusters, balconies, bays etc., but as excessive as such shopping lists of parts now seem, they were not thrown together thoughtlessly.

Not at all. Though rooted perhaps in Europe's showy 19th-century opera houses, this new building type was designed with Everyman (and -woman) in mind. The clear intention was to lure and dazzle an unprecedented mass audience for a new mass medium, and the commanding architectural idea was that of the gesamtkunstwerk -- the total artwork in which each solitary element contributed to the desired overall effect. The silent movies, the vaudeville acts and mighty Wurlitzer organs that played under these proscenium arches were not the only shows -- the architecture itself was a prime source of entertainment.

Eberson's major contribution to the type was to conceive the "atmospheric theater" -- he added the effects of lighting to the total work. His palaces, with their suspended, starry ceilings and all-around architectural embellishment, could be and were modulated by dramatic shifts from brilliance to shadowy depths. The "stars and clouds" formula, it was sometimes called, but it was more than that. It was impure, profuse, exotic, eclectic, kitschy, skilled, thrilling, ooh-and-aah architecture.

An exposition of flat, still materials (drawings and black-and-white photographs, mostly) is not calculated to reproduce such effects, although to a point they can be imagined. Aspects that this exhibition better demonstrates are the skill of the enterprise and the underlying design system.

At its height the Eberson office kept legions laboring away on fine, large linen "sheets" -- we're told a single major project would involve 40 to 50 draftsmen for up to two months. How splendidly they drew. Starting with Eberson's sketches, they would conjure the overall forms and myriad details with tremendous exactitude. Today such working drawings -- for these are what contractors worked from -- would be programmed into a computer, but it's hard to believe that a machine would produce effects at once so quirky and so fantastic. In each of these big drawings we're privileged to see a fantasyland take shape.

Then, too, the architects could take for granted a high level of craftsmanship. "This T.C. {terra cotta} must be equal in strength to the brick work," they could admonish, confident that it would be done. Eberson and, one supposes, his minions also, were sticklers for detail. There's a picture here of the self-confident boss -- rotund, a little flashy with his homburg and floppy, foppy bow tie -- measuring an exotic lamp stand in Richmond's magnificent Loew's Majestic.

At the same time, there was a pattern involved, a formula -- the germ of the computer's rationalized and systematized labor is much in evidence. Details are repeated from drawing to drawing, building to building, city to city; instructions were reduced to the simplest labels: "Texture B." This is hardly surprising: The volume of work was great, the clients demanding, the pressure constant to keep a lid on costs. To look carefully at these drawings is to become aware, lacking any other evidence, of just how big a business was moviedom. Palaces, yes, but not necessarily built for the ages.

This architect's career, in a way, mirrors the fate of the opulent building type: Like the movie studios, Eberson overextended himself during the roaring decade. Early in the Depression, he went bankrupt and had to give up his manor house (and stables and kennels and ponds) in Mamaroneck, N.Y. Overbuilding, ferocious competition, economic disaster, a critical change in technology (from silence to sound in films) -- all are reasonably cited as causes of the decline in movie palace construction. The Octagon show, devoted almost entirely to a six-year span in one architect's output, gives us a vivid sense of the condensed intensity of the period.

Eberson, like the movie studios, adjusted. He rejected overabundance in architecture and decor, though not theatricality and glamour; his office turned out many an attractive movie house in the newer, simpler, forward-looking deco and streamlined styles. The once-proud Silver Theatre in Silver Spring, so badly mistreated by a series of developer-owners, is one; the Penn Theatre on Capitol Hill, now but a frontispiece for an office building, is another.

Tellingly, these newer buildings were not so centrally located -- the movie palaces were almost exclusively a downtown phenomenon. Television is often said to have dealt the palaces a mortal blow, but what really killed so many of them are the same potent forces -- the automobile, suburbanization -- that spelled disaster for all downtowns. The nostalgia one feels in this show is for these fine, wild, weird relics of the '20s, and also for the placemaking centripetal rhythms of urban life, 70 years ago.

The exhibition was organized by architectural historian Jane Preddy, curator of the City University School of Architecture in New York. It continues at the Octagon, 1799 New York Ave. NW, through Jan. 20. The American Architectural Foundation will host a panel discussion on Eberson's work on Jan. 10; call 202-638-3221 for details.