The autograph manuscript of Sergei Rachmaninov's Second Symphony, long thought lost, was recently discovered on the estate of a European private collector. On Dec. 7, it will go up for auction at Sotheby's in London with a presale estimate of £300,000 to £500,000 ($550,000 to $920,000). Sotheby's has not revealed the identity of the collector, nor is it known how the manuscript came into his or her hands. What the auction house did say was that its authenticity had been confirmed by Geoffrey Norris, a Rachmaninov authority and chief music critic at The Daily Telegraph, after he was approached by the estate's executor. "The handwriting, the paper and the manner in which Rachmaninov made corrections — all are as they should be," Norris later wrote. The discovery is of major significance, in part due to the importance of the Second Symphony in Rachmaninov's creative output. A lush, grandly proportioned work in the late Romantic tradition, the Second Symphony is perhaps the finest and undoubtedly the most frequently performed and recorded of the composer's purely orchestral works. Only the Second and Third Piano Concertos rival it in popularity. In musical manuscript parlance, an "autograph manuscript" is a continuous copy written out by the composer in more or less final form, including orchestration. This is distinct from preliminary sketches and drafts, and from later manuscript copies made by someone else. Autographs often include corrections or revisions that shed light on how the work reached its final form.