a violist, wrote a substantial amount of music for viola, including the concerto Der Schwanendreher. Form The viola is similar in material and construction to the violin. A full-size viola's body is between and longer than the body of a full-size violin (i.e., between ), with an average length of . Small violas typically made for children typically start at , which is equivalent to a half-size violin. For a child who needs a smaller size, a fractional-sized violin is often strung with the strings of a viola. Unlike the violin, the viola does not have a standard full size. The body of a viola would need to measure about long to match the acoustics of a violin, making it impractical to play in the same manner as the violin. For centuries, viola makers have experimented with the size and shape of the viola, often adjusting proportions or shape to make a lighter instrument with shorter string lengths, but with a large enough sound box to retain the viola sound. Prior to the eighteenth century, violas had no uniform size. Large violas (tenors) were designed to play the lower register viola lines or second viola in five part harmony depending on instrumentation. A smaller viola, nearer the size of the violin, was called a vertical viola or an alto viola. It was more suited to higher register writing, as in the viola 1 parts, as their sound was usually richer in the upper register. Its size was not as conducive to a full tone in the lower register. Several experiments have intended to increase the size of the viola to improve its sound. Hermann Ritter's viola alta, which measured about , was intended for use in Wagner's operas. The Tertis model viola, which has wider bouts and deeper ribs to promote a better tone, is another slightly "nonstandard" shape that allows the player to use a larger instrument. Many experiments with the acoustics of a viola, particularly increasing the size of the body, have resulted in a much deeper tone, making it resemble the tone of a cello. Since many composers wrote for a traditional-sized viola, particularly in orchestral music, changes in the tone of a viola can have unintended consequences upon the balance in ensembles. One of the most notable makers of violas of the twentieth century was Englishman A. E. Smith, whose violas are sought after and highly