For two weeks, like Atlantis rising from the sea, the Coolidge Auditorium was with us again -- filled, as it should be, with beautiful chamber music. After a whole season deprived of that splendid little concert hall, Washington music lovers flocked to the five concerts of the Library of Congress Summer Chamber Festival, which ended Tuesday night with a glorious performance of Mendelssohn's Quartet in B Minor, Op. 3 -- a work that he wrote at 15 and that any composer at any age might be proud to claim.

"Well, this is it," the festival's artistic director, Miles Hoffman, told the audience before sitting down to play his viola in this final number. "Thank you all very much for coming, and we'll see you next year." Although remodeling will block off Coolidge Auditorium for at least another season, the Library of Congress will offer a limited number of concerts next season at the National Academy of Sciences.

Next year's concerts should be good, but it will not be the same as concerts in the Coolidge, a room notable for its acoustics and the scene of many historic performances; a focal point in a great collection of music texts and instruments; a place where you could always expect to pass an interesting music exhibit while strolling in. There was a special joy in seeing the old room still intact, give or take a few patches of peeling paint. And there was nostalgia for the time when it held first-class free concerts every Friday night.

This year's festival went out on a strong note; the Mendelssohn is an instantly likable work, full of grace and vitality, and it was played with a precise coordination that did not undermine spontaneity. Hoffman was joined in this music by violinist Alexis Galperine, cellist Julia Lichten and pianist Ann Schein. In Ernest Bloch's solid and deeply involving Quintet No. 2 for piano and strings, the group also included violinist Elisabeth Adkins; the performance was superbly coordinated.

The effect was more mixed in the rest of the program: two works of Francis Poulenc. In the "Elegie" for horn and piano, hornist Anthony Cecere, ably partnered by pianist Edmund Battersby, showed exemplary technique and played expressively within the instrument's rather limited range. Four other players joined these two in Poulenc's Sextet -- flutist Toshiko Kohno, clarinetist Loren Kitt, oboist Gerard Reuter and bassoonist Lynette Diers Cohen. Each played some fine solos, but their ensemble playing often failed to blend smoothly, and often the whole seemed less than the sum of its parts.