In the two works that immediately followed the first quartet , Bowen finds the Piano Sonata No. 1 ( 1938 ) full of the young composer 's inventiveness , while Matthews writes of the Concerto for Double String Orchestra ( 1939 ) : '' ( I ) t is the rhythmic freedom of the music , its joyful liberation from orthodox notions of stress and phrase length , that contributes so much to its vitality '' .
One of his best-known works is the Concerto for Double String Orchestra ( 1938-1939 ) .