The Chopin nocturnes constitute 21 short pieces for solo piano written by Frédéric Chopin between 1827 and 1846. They are generally considered among the finest short solo works for the instrument and hold an important place in contemporary concert repertoire. Although Chopin did not invent the nocturne, he popularized and expanded on it, building on the form developed by Irish composer John Field. The nocturnes numbered 1 to 18 were published during his life, in twos or threes, in the order of composition. Numbers 19 and 20 were actually written first, prior to Chopin's departure from Poland, but published posthumously. Number 20 was not originally entitled "nocturne" at all, but since publication in 1870 as such, is generally included with publications and recordings of the set. Chopin composed his most popular Nocturne in E-flat major, Op. 9, No. 2 when he was about twenty. This popular nocturne is in rounded binary form (A, A, B, A, B, A) with coda, C. The A and B sections become increasingly ornamented with each recurrence. The penultimate bar utilizes considerable rhythmic freedom, indicated by the instruction, senza tempo (without tempo). Nocturne in E-flat major opens with a legato melody, mostly played piano, containing graceful upward leaps which becomes increasingly wide as the line unfolds. This melody is heard again three times during the piece. With each repetition, it is varied by ever more elaborate decorative tones and trills. The nocturne also includes a subordinate melody, which is played with rubato. A sonorous foundation for the melodic line is provided by the widely spaced notes in the accompaniment, connected by the damper pedal. The waltz-like accompaniment gently emphasizes the 12/8 meter, 12 beats to the measure subdivided into four groups of 3 beats each. The nocturne is reflective in mood until it suddenly becomes passionate near the end. The new concluding melody begins softly but then ascends to a high register and is played forcefully in octaves, eventually reaching the loudest part of the piece, marked fortissimo. After a trill-like passage, the excitement subsides; the nocturne ends calmly.