But from the beginning of bar No. 2 it is necessary to make only the simple gestures:—
on account of the triplet on the third beat, and on account of the one following it which the double gesture would much interfere with.
In the famous ball-scene of Mozart's Don Giovanni, the difficulty of keeping together the three orchestras, written in three different measures, is less than might be thought. It is sufficient to mark downwards each beat of the tempo di minuetto:—
Once entered upon the combination, the little allegro in 3⁄8, of which a whole bar represents one-third, or one beat of that of the minuetto, and the other allegro in 2⁄4, of which a whole bar represents two-thirds, or two beats, correspond with each other and with the principal theme; while the whole proceeds without the slightest confusion. All that is requisite is to make them come in properly.
A gross fault that I have seen committed, consists in enlarging the time of a piece in common-time, when the author has introduced into it triplets of minims:—
In such a case, the third minim adds nothing to the duration of the bar, as some conductors seem to imagine. They may, if they please, and if the movement be slow or moderate, make these passages by beating the bar with three beats, but the duration of the whole bar should remain precisely the same. In a case where these triplets occur in a very quick bar in common-time (allegro-assai), the three gestures then cause confusion, and it is absolutely necessary to make only two,—one beat upon the first minim, and one upon the third. These gestures, owing to the quickness of the movement, differ little to the eye, from the two of the bar with two equal beats, and do not affect the movement of those parts of the orchestra which contain no triplets.
