The anonymous and untitled 18th-century music book is being described by experts as one of the most significant discoveries of recent decades, the library's director, Gilles Pécout, said on Friday.
The use of French paper, as well as the content - composition exercises and seven pieces for flute and harp - suggest, according to the institution, the manuscript originates from the lessons given by Wolfgang Amadeus Mozart between May and July 1778 during his final stay in Paris.
His pupil was Marie-Louise-Philippine de Guînes, a talented harpist from an aristocratic family of musicians.
The music book, which was discovered in February in the institution's collections - one of the largest libraries in the world - sheds new light on Mozart's final stay in Paris.
It also reveals the young teacher Mozart in his day-to-day work - an aspect of his creative output that has hitherto been scarcely documented.
The book, in which the handwriting of the teacher and pupil lie side by side, appears to document the final lessons. The last exercise remained unfinished, and six pages at the back of the book are blank - as if the work had end abruptly.
In fact, the lessons ended with the wedding of Mademoiselle de Guînes on July 26, 1778.
The composer was born in Salzburg in 1756 and died in Vienna in 1791 aged 35.
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