The manuscript of a composition for soprano and harpsichord, discovered two weeks ago in a shoe box in Weimar, Germany, has been authenticated as a previously unknown early work by Johann Sebastian Bach (1685-1750), the Bach Archive in Leipzig announced yesterday.

Harvard University professor Christoph Wolff, a leading expert on Bach's life and art, flew to Germany to help authenticate the score. He called the newly discovered piece "an exquisite and highly refined strophic aria, Bach's only contribution to a musical genre popular in late-17th-century Germany." In a strophic piece, all of the verses are sung to the same music, without substantive variation.

The five-minute work was apparently composed in October 1713 by the 28-year-old Bach as a birthday present for one of his patrons, Duke Wilhelm Ernst of Saxe-Weimar.

The manuscript was found amid the clutter of a box that also contained more than 100 poems and congratulatory letters written by others in celebration of the same birthday. According to a report in the London newspaper the Guardian, the library in Weimar where material pertaining to the duke had been stored for several centuries recently burned down, but by chance, the box containing the score had already been removed. Michael Maul, a researcher at the Bach Archive, discovered it while conducting research on the composer's sparsely chronicled life.

"After Michael and I had identified it as Bach's, we opened a very expensive bottle of champagne," Peter Wollny, the archive's head of research, told the Guardian on Monday. "Michael came back from Weimar two weeks ago and said he had found something interesting. We got the microfilm of the score last week. We compared it with Bach's known compositions -- and bingo.

"The last time anything by Bach was discovered was 80 years ago. So far we've only heard it on the computer. But it's a charming little work, written for one singer -- a soprano -- and a harpsichord. There's a little postlude at the end for a string ensemble -- two violins, a viola and a cello. It takes just four or five minutes to play."

The archive has asked British conductor John Eliot Gardiner to present the world premiere and record the aria. Gardiner said that he thought the aria likely came from a longer cantata.

"It is absolutely beautiful," Gardiner told the Guardian on Monday. "So many of Bach's cantatas went missing after he died. His son Wilhelm Friedemann Bach was pretty profligate with his father's stuff. He sold manuscripts off, lost them, used them as firelighters. So when something like this turns up, it is wonderful."

Gardiner described it as "a reflective, meditative, soothing piece, as Bach's church music so often is. It's not going to set the world alight -- enough of Bach's music from this early-to-mid period has survived to give us a sense of his musical personality at that time -- but it's just great to have this, because every one of his cantatas and arias is on a completely different level from all of his contemporaries."

British music critic Tom Service, who has examined the score, wrote in yesterday's Guardian that it is "a charming tune in C major, full of a natural pastoral joy, an appropriate gift for the birthday of his patron in Weimar."

"There's none of the contrapuntal seriousness that you associate with Bach's most involved music," he added. "Instead, this piece reveals an intimate side to the composer."

Bach was highly prolific, and there is already a great deal of his music out there that is rarely heard. Indeed, only in the past quarter-century have all of Bach's 200-odd cantatas -- choral works he turned out, Sunday after Sunday, for use in church services -- been recorded. Still, the modern premiere of this aria, unheard for almost 300 years, promises to be one of the most eagerly anticipated classical music events of the season, and should take place before the end of the year.

In a statement released by the archive, Prof. Wolff called Maul "a most resourceful researcher. In less than three years he uncovered an unparalleled number of new archival Bach documents, but this is the first time he presented a musical discovery. The overall research project is far from being over, and I am quite sure that sooner or later Michael Maul will make news again."

This previously unknown score by Bach, written for soprano and harpsichord, was found in Germany.

The five-minute work was composed in 1713 by the 28-year-old Bach as a birthday present.