With the ophicleide or later, the tuba subjoined to the trombone trio during the 19th century, parts scored for the bass trombone rarely descended as low as parts scored before the addition of either of these new low brass instruments. Only in the early 20th century did it regain a degree of independence. Experiments with the trombone section included Richard Wagner's addition of a contrabass trombone in "Der Ring des Nibelungen" and Gustav Mahler's and Richard Strauss' augmentation by adding a second bass trombone to the usual trio of two tenor trombones and one bass trombone. The majority of orchestral works are still scored for the usual mid- to late-19th-century low brass section of two tenor trombones, one bass trombone, and one tuba.