This painting is probably the canvas entitled École de danse that Degas entered in the fourth exhibition of the Impressionists in 1879. It then belonged to the artist’s close friend Henri Rouart, and it was sold after Rouart’s death in 1912 along with a number of other important works by Degas. Mr. Frick was the next private individual to own it, acquiring the painting a year and a half later.
The Rehearsal is one of many compositions devoted to the dance that the artist produced in the 1870s, apparently fascinated with the mechanization of the human body that the rigorous discipline of the ballet imposed. In the same exhibition of 1879 Degas showed two other pictures of dancers practicing with a violinist. In all of them the unidentified musician appears divorced from the events surrounding him, his age and stolid form providing a touching contrast to the doll-like ballerinas.
Source: Art in The Frick Collection: Paintings, Sculpture, Decorative Arts, New York: Harry N. Abrams, 1996.