=Groups in the Orchestra=.—The orchestra is composed of groups of instruments allied by similarity of construction. The usual classification is into three main groups, =strings=, (bowed instruments), =wind= and =percussion= instruments. In the former are included the violins, viola, violoncello and double or contra-bass; =wind= instruments subordinate into =wood wind= and =brass=, the former include instruments of the flute, oboe, bassoon and clarinet families, the latter horns, trumpets, trombones, tuba or other bass instruments; the =percussion= includes kettle drums, other drums, triangles, cymbals, etc.; the =harp=, while a stringed instrument, is not included in that class. These instruments offer a great variety of effects, singly and in many possible combinations, in the peculiar effects possible by variety in playing, which in bowed instruments is considerable, and particularly by contrast with each other. While the orchestra today is in a highly developed condition, composers are seeking to extend the limits of their art by the use of more elaborate and subtle forms; so that we cannot in any wise predict the course and limits of absolute music with the almost unlimited resources at its disposal in the modern orchestra. =Purpose in Combination=.—When we consider the orchestra as a combination of instruments we must bear in mind that this combination is the result of a definite purpose to produce music independent of restrictions such as were shown to have existed in the days of the domination of the Church. The composers of the early polyphonic period and up to the 17th century bent their efforts to the composition of choral music which was sung for many years without instrumental support. When later the organ, and still later, viols and other instruments were drafted into the service of church music, the accompaniments were not independent of the voice, but merely doubled the various parts. Composers thought in _terms of voices_ and their limitations, _not in_ the greater range and endurance of _instruments_. Then, too, the instruments were crude and their tone lacked distinctiveness as well as the comparative sweetness and purity of the vocal music of that day. Combinations of instruments existed in the Middle Ages, but not according to a system, and were due to the executants who assembled them rather than to the demand for them in the works of composers. It was in the attempts at light dramatic music that preceded the establishment of the opera that instruments were grouped together, showing a great weakness, from our point of view, in stringed instruments played with the bow, and a corresponding preponderance of brass.