Joseph Cornell is the poet of all the people who ever went up to the attic to find an old tax return in the steamer trunk -- and spent the whole afternoon.

He put things into boxes. The way he did it makes one of those boxes worth about $50,000 today -- a kind of three-dimensional collage. He used to sell them for $10.

It seems only right that Cornell's artistic estate should wind up in 50 big movers' cartons. There they sit in a room at the National Collection of Fine Arts, which will soon open a study center to collate material he left: the stuff of his mysterious little worlds.

The collagist's sister, Betty Voorhees Benton, has given it to NCFA, and Lynda Hartigan, a Cornell specialist, is now cataloguing it.

"Walter Hopps suggested the study center," Hartigan said. "Mrs. Benton was excited about it because Cornell, while he was a private person, was no recluse. We have display shelves, and maybe there'll be a changing exhibit of featured items. Mostly it'll be kept in the cartons."

There's a whole Christmas-bulb box full of little red plastic lobsters. There's a Japanese disappearing coin trick (one of those sliding wooden things), into which he put a coin-sized drawing. There's a working penny arcade, and a whirling sparkler disc that you pump like a hypodermic and for which he made his own fantastic discs.

There are antique toys and games; glass domes containing pirouetting cardboard dancers; a harlequin marionette with an old map pasted to the back (you always turn over Cornell pieces: He loved to put surprises on the back).

And: canary cages; tintypes; old Caruso records; clay pipes; sheet music for the Christy Minstrels an early version of the Thimble Forest box; posters; an envelope of blue glitter: a Christmas present for Katherine Sergava of the Mordkin Ballet; dolls; compasses; a souvenir History of New York; boxes stuffed with photostat strips a Caravaggio reproduction; diaries; family snapshots; cordial glasses; wooden dowels movie stills; pictures of Zizi Jeanmaire, another ballet dancer he admired; old visiting cards; a tiny globe, children's blocks; paper butterflies; shells; "Movies for the Millions" by Gilbert Seldes; picture puzzles, and elaborately decorated matchboxes containing tightly rolled fragments of writing apparently torn from French history books...

"We hope the dexhibit will be a dialogue between the finished works and the material he drew from," said Hartigan. Some of the structures seem to be studies for later boxes, larger or smaller versions, in effect, notes. The study center will be open to scholars, students, collectors and others with special interest in Cornell. Because much of the stuff is very perishable, it is being stored in the cartons when not actually being studied.

"It's really not proper to drily dissect Cornell's work, I think, but it does have elements that can be analyzed. He was a cultural historian, basically. We also have some samples of projects he did in his various jobs."

After graduating from Andover in 1921, he lived with his family on Long Island until the stock market crash sent him out to earn money where he could.He was a designer for the Traphagen textile studios (some of his patterns are in the collection), a freelance artist for Conde Nast (these too), did covers for the Bride's Reference Book and Dance Index (which are two-dimensional versions of his boxes), as well as fantasy collages for View magazine in the '40s.

Hartigan has retrieved all the components of these collages: a litho of Niagara Falls, old cartes de visite, photo negatives and so on.

From the early Depression until his death in 1972 he lived with his mother and brother Robert in the rambling house on Utopia Parkway in Flushing, N.Y., gradually filling the place with his found art until it spilled out of the attic, the basement, the garage.

"The family decided to let him concentrate on his work as much as possible. At first he would sell a piece for $10, but by the '60s he had a good market. He was a good businessman, though he did tend to trust dealers too much, and he could be quirky about favorite works. A collector would see some box in his house and want it, but he wouldn't let him have it."

Today even a Cornell paper collage goes for $8,000 to $12,000.

"Even in his lifetime he was getting several thousand for a single work. He'd get upset if he did a piece for someone and they went and sold it."

He also worked on avant-garde films with Jonas Mekas and Stan Brakhage, whose work strikes a chord in its fascination with odds and ends.

The Cornell themes emerge clearly from this collection: theater and ballet, celestial navigation, classical music, European hotels, 19th century dancers, small animals, games, the 3rd Avenue El.

"He wasn't afraid to be sentimental," the curator said.

But then, sentiment is the mortar of memory.