Six Sonatas in Trio for two oboes and harpsichord[372] appear to date from about 1696, when he was eleven years old, and while he was still at Halle, where he wrote as he said, "like the devil," above all for the oboe, his favourite instrument. They are in four movements: _adagio_, _allegro_, _adagio_, _allegro_. The slow movements are often very short, and the second between them is sometimes a mere transition. The Sonata for _Viola da Gamba_, and _Cembalo Concertato_ in C Major[373] probably belongs to 1705, when Handel was at Hamburg. It is the only one of its kind in the works of Handel, which shows him as a forerunner of Bach. The sonata is in trio form. The clavier plays a second _obbligato_ besides the bass part, as Seiffert notes: "Ten years before Bach worked at his Sonatas with accompaniment for _cembalo obbligato_, Handel had already a clear perception of their value." Three Sonatas for Flute and Bass,[374] of an elegiac grace, also perhaps date from the Halle period, and according to Chrysander seem to have been continued up to 1710 at Hanover. But the chief instrumental chamber works written by Handel were published in London between 1732 and 1740, and they comprise three volumes:[375] (1) Fifteen sonatas or solos for a German flute, oboe or violin, with a thorough bass for the harpsichord, or bass violin, Op. 1. (2) Nine sonatas or trios for two violins, flutes, or oboes, with a thorough bass for the harpsichord, or violoncello, Op. 2. (3) Seven sonatas or trios for two violins, or German flutes, with a thorough bass for the harpsichord, or violoncello, Op. 5. The first volume contains very old pieces, of which some date from the time when Handel was at Burlington and Chandos. Others might have been intended for the Prince of Wales, whose violin teacher, John Dubourg, was a friend of Handel, as they date from about 1730. The second volume appeared at first in Amsterdam, afterwards in London with Walsh, under a French title[376] in 1733. The third volume was composed in 1738, and published about the beginning of 1739.[377] The first feature to notice in general is the want of definition in the choice of instruments for which this music was written. Following the same abstract æsthetic of his time, the composer left it to the players to choose the instruments. However, there was no doubt that in the first conception of Handel certain of these pieces were made for the flute, others for the violin, and others for the oboe. In the volume Op. 1 of the solo sonatas (for the flute or oboe, or violin) with bass (harpsichord or violoncello), the usual form is generally in four movements:[378] _adagio_, _allegro_, _adagio_, _allegro_. The slow pieces are very short. Several are inspired by the airs of Italian cantatas and operas. Some of the pieces are joined together.[379] The harmony is often thin, and requires to be filled in.