and again, these characteristics of detail must be subordinated to the main idea of producing a well-formed whole. A due balance of parts can only be produced by compliance with the conditions of a musical work of art. The substance and form of these ensemble movements are of course subject to many modifications; many of them are nothing more than a detailed and fuller exposition of some definite situation or mood; and their whole design is therefore simple. Such are the duets between Figaro and Susanna (Act I., i, 2), between Susanna and Marcellina (Act I., 5), the writing duet (Act III., 5), and the duet between the Count and Susanna (Act III., 1); they are distinguished from airs more by their form than their nature. If during the dressing scene Cherubino were to chime in with Susanna's remarks, the Countess were also directly to interpose, such a duet or terzet would represent the situation in greater variety of detail, the form would become richer by means of contrasting {ENSEMBLES.} (101) elements, but the musical matter would not differ essentially from that to which we are accustomed in solo airs. The terzet in the second act is of this character; a situation or a mood is maintained, and only variously mirrored in the various personages. Here, then, is the point of departure for unity in the grouping of the whole; and the ordinary resources of musical construction, such as the repetition of a motif in different places, the elaboration and combination of the motifs, for the most part lend themselves to the situation. The difficulty of the task increases in proportion as the music forms part-of the plot. We have an instance of this in the duet between Susanna and Cherubino (Act II., 5); when the latter tries to escape, and finally jumps out of the window. The simple situation gives rise to an expression of fear and disquiet in short, interrupted motifs, and the prevailing characteristic is an agitation almost amounting to action__in progress. The agitation, however, is so characteristically rendered by the music, that, while appearing to flow from an irresistible impulse, it is in reality only an effect of a definite musical formula fitly working out a given motif. The orchestral part forms a separate piece of music of very varied character.[33] The terzet of the first act comes in the very middle of the action (Act I., 7). Here we have not merely three persons of dissimilar natures thrown together, but at the particular point in the plot their interests and sentiments are altogether opposed, and each of them is influenced by different suppositions. The plot proceeds, however, and the discovery of the page in the arm-chair gives a turn to affairs which changes the position of each person present. We are struck in the first place with the striking, delicately toned musical expression, especially when the voices go together, as at the beginning, when the Count's anger: "Tosto andate e scacciate il {LE NOZZE DI FIGARO.} (102)