Woodwind did appear in the earliest orchestras, though infrequently and secondary to the strings - usually it would include two oboes and a bassoon, with flutes sometimes replacing the oboes. Throughout the baroque period, the basso continuo was an essential part of the scoring. The treble and bass were strongly emphasized, while the middle parts were often left to the continuo alone. The orchestra was rather small at this time; Bach had as few as 18 players, and Handel usually used about 30.
As time continued, the classical orchestra became more established through the disuse of the continuo and the acceptance of the clarinet. The abandonment of the continuo meant there was a much greater freedom in the string parts, as they now had to fill the harmony in. Instead of both violin parts doubling the melody and the violas, cellos and basses doubling the bass, there were now four distinct parts. The clarinet, like the flute, first appeared as an alternate for the oboe, but in the late works of Haydn and Mozart the orchestra was standardized, with pairs of flutes, oboes, clarinets, bassoons, French horns and trumpets, in addition to the strings. All the wind instruments could carry the melody, meaning there was a more colourful tone in the orchestra.
Towards the end of the Classical period Beethoven brought about some innovations in orchestral arrangement; these included the addition of instruments such as the piccolo, double bassoon and bass drum. The scores for cello and bass in his works were separated, which was uncommon for that time. It is mainly due to him that the standard woodwind section was fixed to be the ‘double wind’ configuration, with 2 of each instrument. The brass section was also enlarged, for example his 9th Symphony required 4 horns. These changes required a larger string section to balance the overall sound of the orchestra, and this in turn led to an increase in the power of the orchestra.
In the Romantic period, not only was there a marked change in the size of the orchestra, but there was also a change in the style of music they performed; composers tended to experiment with the harmonies, leading to the use of discords to heighten emotional effects. Melodies also became more song-like.
The period saw the orchestra assume great magnitude compared to what had gone before. Advances in technology and the resultant opportunities available to composers encouraged this growth. Technology provided the valves for brass instruments and the resultant range and flexibility allowed certain musical forces that were unavailable previously. The arrival of the tuba completed the brass section that now, thanks to valves and full section membership, could easily dominate the combined efforts of the other sections. The range and number of instruments increased adding another new dimension to the forces available.
To maintain balance, composers would score for three or four of each member of the woodwind family and the double bassoon, along with the piccolo, bass clarinet and cor anglais, was introduced. Also to maintain balance, the number of strings was increased.
Composers such as Berlioz and Wagner would use every musical force at their disposal. Music with great emotion was produced. Every accent, tempo variation and dynamic change was exploited to create scores with rich colour, texture and tone. These forces would all be emphasised by the larger orchestras now in place.
The scores of Mozart and Beethoven generally required an orchestra of about 40; those of Weber and early Wagner called for about 55, however Wagner's Ring cycle called for about 110. Berlioz in particular was very influential in increasing orchestral colour and in encouraging the use of a larger orchestra; his Traité d'orchestration, a fundamental work of its kind, envisioned an ideal orchestra of 465.
In his Symphonie fantastique, Berlioz adopts the extreme emotions and drama of the opera house, telling the story of a young, unhappy, and ultimately suicidal lover (Berlioz himself). The piece is bound together by a recurring, representative musical theme - the famous "fixed idea." This kind of opera-like piece was very representational of the romantic era.
It was during the nineteenth century also that the role of conductor became established. Previously, the togetherness was the responsibility of the first violin and/or the harpsichordist but the numbers of musicians and forces involved in the performance of works by Romantic composers required a more precise method of control.
All the experiments with orchestration that took place in the romantic era showed the way to the 20th century, and the 20th century orchestra retained the basic structure achieved when string, woodwind, brass and percussion sections were established.
Stravinsky's Rite of Spring shows the early 20th century interest in diverse instrumental combinations and original use of the instruments' capabilities. In general, composers of the 20th century have continued exploring novel uses of instruments and have preferred a moderate-sized orchestra. Seventy-five to ninety players is adequate for most 20th century scores. However a reduced or chamber orchestra of classical or baroque dimensions has also been much used. In this century the percussion section is used more prominently; new instruments have been devised and the playing of old ones varied.
Overall, The 20th century has been a century of freedom and experimentation with the orchestra. It has also been a time of more well-known conductors, as the conductor has more and more responsibility and visibility. The "basic" 19th century orchestra is still around, and composers will sometimes add or subtract instruments, depending on the effect they want to get. You might see an expanded percussion section, or lots of woodwind and brass. However, the orchestra does still takes more or less the same form: a big string section, with smaller sections for brasses, woodwinds, percussion, harps and keyboard instruments. After all these years, the main outline of the orchestra is still there and continuing to produce new music.