(Music Sales America). In April 1925, Holst wrote to his friend Edwin Evans, saying: "I am working on something that will probably be either chamber music or waste paper". The work was this Terzetto for flute, oboe and viola. It was the only mature piece of instrumental chamber music he ever wrote. Audiences of half a century ago were not used to listening to music in three keys, and at first even Holst himself had doubts about it; he needed to hear it several times before he could be sure that he liked it... Sheet Music for Flute, Oboe and Viola or Clarinet.