The complete establishment of the quartet as an art-form worthy to rank beside the symphony is due to Beethoven. The list of Beethoven's chamber music comprises the following: two octets in E-flat for wind, one septet for strings and wind, one sextet in E-flat for strings and wood, one sextet in E-flat for wind, two quintets for strings, sixteen quartets for strings, two "Equali" for four trombones, five trios for strings, one trio for strings and flute, one trio for wind, three duos for wind, one quintet for piano and wind, one quartet for piano and strings, eight trios for piano and strings, ten sonatas for piano and violin, five sonatas for piano and 'cello, and a few other works. The trios are uncommonly fine compositions, but the quartet was Beethoven's especial choice among chamber music forms, and he used it for the embodiment of some of his noblest thoughts. All that has been said about his treatment of the piano sonata and the symphony applies to his treatment of the quartet. Beethoven could not by any possibility take up such a peculiarly intimate form of music without infusing into it a new life. He made it the vehicle for the expression of a marvellous depth of feeling. In doing so he made variations in the established form, but without overthrowing or ignoring any of its fundamental principles. Sir George Grove says, "The obscurity and individuality of the thoughts themselves, and their apparent want of connection until they have become familiar, is perhaps the cause that these noble works [the later quartets] are so difficult to understand." But it is generally conceded by critics and musicians that Beethoven's quartets, particularly those in F, E minor, and C, dedicated to Count Rassoumoffsky, and called the "Rassoumoffsky Quartets," are the noblest specimens of chamber music extant. In his "Life of Mozart" Otto Jahn says:-- "The string quartet offers the most favorable conditions for the development of instrumental music, both as to expression and technical construction, giving free play to the composer in every direction, provided only that he keep within the limits imposed by the nature of his art. Each of the four combined instruments is capable of the greatest variety of melodic construction; they have the advantage over the piano in their power of sustaining the vibrations of the notes, so as to produce song-like effects; nor are they inferior in their power of rapid movement. Their union enables them to fulfil the demands of complete harmonies, and to compensate increase of freedom and fulness for the advantages which the pianoforte possesses as a solo instrument." OPENING OF SLOW MOVEMENT OF BEETHOVEN'S SEVENTH QUARTET. [Music: _Adagio molto e mesto._ VIOLIN 1. VIOLIN 2. VIOLA. 'CELLO.]