Every play had its own musical prelude, which distinguished it from others, and from which many of the audience at once knew what piece was about to be performed(601). The chief musical instruments employed in the theatre were the _tibiæ_, or flutes, with which the comedies of Terence are believed to have been represented. The _Andria_ is said to have been acted, “Tibiis paribus, dextris et sinistris;”—the _Eunuch_, “Tibiis duabus dextris;”—the _Heautontimorumenos_, on its first appearance, “Tibiis imparibus;” on its second, “Duabus dextris;”—the _Adelphi_, “Tibiis sarranis;”—the _Hecyra_, “Tibiis paribus,”—and the _Phormio_, “Tibiis imparibus.” It thus appears, that the theatrical flutes were classed as “dextræ et sinistræ,” and also as “pares et impares,” and that there were likewise “Tibiæ Serranæ,” or “Sarranæ,” to which, it is believed, the Phrygiæ were opposed. There has been much dispute, however, as to what constituted the distinction between these different sets of pipes. Scaliger thinks, that the “Tibiæ dextræ et sinistræ” were formed by cutting the reed into two parts: that portion which was next to the root making the left, and that next to the top the right flute.—whence the notes of the former were more grave, and those of the latter more acute(602). Mad. Dacier, however, is of opinion, that flutes were denominated right and left from the valves, in playing, being stopped with the right or left hand. There is still more difficulty with regard to the “Tibiæ pares et impares.” Some persons conjecture, that the Tibiæ pares were a set of two or more pipes of the same pitch in the musical scale, and Impares such as did not agree in pitch(603). The opinion, that flutes were called Pares when they had an even, and Impares when an odd number of valves, is not inconsistent with this notion; nor with that adopted by Dempster(604), that the difference depended on their being equal or unequal distances between the valves. It may be also reconciled with the idea of Salmasius, that when the same set of flutes were employed, as two right or two left, a play was said to be acted Tibiis paribus; and, when one or more right with one or more left were used, it was announced as performed Tibiis imparibus. This idea, however, of Salmasius, is inconsistent with what is said as to the _Andria_ being acted with equal flutes right and left; unless, indeed, we suppose, with Mad. Dacier, that this is to be understood of different representations, and that the flutes were of the same description at each performance, but were sometimes a set of right, and at other times a set of left flutes.