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A book-length manuscript chiefly in the hand of J.S. Bach. He wrote it for the education of his ten-year-old son, so he included important information that he normally didn't spell out, such as instructions on ornaments and fingering. The music is from the Well-Tempered Clavier, the Two- and Three-Part Inventions, and other works; some of them differ from the standard versions of these pieces. Eva Judd O'Meara was the librarian who acquired the manuscript for Yale. You can listen to her reminiscences about it. (Scroll down.) Music Deposit 31.
Full score, with all the first movement, most of the second, and none of the third. The concerto was written ca. 1720, but not published until ca.1850. The manuscript is a signed presentation copy from Felix Mendelssohn (1809-1847) to Ferdinand David (1810-1873), dated 19 January 1841. Some marking may be David's.
Beinecke Osborn Music MS 528
(Scroll down.) This manuscript created a global sensation in 1984, when Bach scholar Christoph Wolff announced that it contained 33 otherwise unknown chorale preludes attributed to J.S. Bach. Ma21 Y11 A30 LM4708.