Orchestra (Gr., from to dance), that part of the Greek theatre in which the chorus performed its dances and evolutions. It was circular, except that a segment was appropriated to the stage, in front of the spectators, and surrounded by steps. In modern theatres the orchestra is the space between the audience and the stage allotted to the musician; and in concert rooms it is a raised platform occupied by both vocal and instrumental performers. Previous to the commencement of the 18th century the instrumental performers in theatres were placed in a box on the side of the stage and out of view of the greater part of the audience. - The term orchestra is more commonly applied to a body of instrumental performers in which the violin family predominates. A body of musicians using principally wind instruments is popularly called a band. One of the earliest examples of the composition of an orchestra is afforded by Rinuccini's opera Euridice (1600), in which the instrumental part was sustained by a harpsichord, a large guitar, a viol, a large lute, and flutes. In Monteverde's opera of Orfeo, performed in 1604, 35 instruments were employed, including 17 of the violin species, and 12 wind instruments, chiefly to accompany the voice, although only a few of them were played at the same time.

Subsequently the stringed instruments were increased, to the almost total exclusion of other kinds, and the works of Cavalli, Carissimi, and Lully are written principally for violins, violas of different degrees of power, bass viols, and double bass viols. Bach composed a number of symphonies for orchestra. They were written for two horns, two flutes, two hautboys, violins, viola, violoncello, piano (Flügel), and double bass. Lully sometimes employed flutes, bassoons, and trombones; but it was not until after the time of Haydn's later works that the wind instruments, whether of brass or wood, began to be recognized as an indispensable part of the orchestra. The smallest number of performers in a grand orchestra is estimated at 60, and the hall wherein they play should be of moderate size; but for the greatest effects 100 and upward must be employed. The instruments of which the modern orchestra is composed are of three classes, stringed, wind, and pulsatile, as follows:

STRINGED.

WIND.

PULSATILE.

First violins.

Flutes.

Kettle drums.

Second violins.

Hautboys.

Cymbals.

Violas.

Clarinets.

Triangle.

Violoncellos.

Bassoons.

Double basses.

Horns.

Trumpets.

Trombones.

To these instruments modern composers occasionally add others for special effects, such as the harp, pianoforte, corno Inglese, organ, tuba, bells, and bass and snare drums.