During the second bar of six beats the accompaniment (not given here) takes its cue from the melody and divides the quaver beats by 3 (and the crotchets by 6). This motion thereafter per vades the whole composition, sometimes in the melody, and always in the accompaniment, except when the whole orchestra pauses. These triplet semiquavers become equivalent to the aver age length of syllables in speech-rhythm, and the mind auto matically measures all pauses by them. Besides the indeterminate grace-notes there are definite shorter values.
No rhythm in poetry or prose ever contemplated giving one syllable seven times the length of another, as we see in the double dotted quavers with their complementary demisemiquavers. But in the fifth bar we have the whole six beats occupied by one sus tained note, eighteen times the length of the average syllable. Yet so cogent is the body-rhythm of these long and complex bars that a deviation from the symmetry of an 8-bar period is per missible only when a change of key introduces new topics, as happens immediately after this quotation. But this will lead us to the separate topic of phrasing. Irregularities in the lengths of the bars themselves would be quite impossible, except in the case of a dramatic or final pause. Haydn has one opportunity for a dramatic pause in the course of the movement, yet he does not leave it at that, but expands it to two entire normal bars filled with organized rhythms.
Musical rhythm is not often as ornate as this, nor is this elabora tion capable of much contrast or development, but the example at once carries us far away from the rhythms of poetry and includes all the musical principles so far mentioned. From it we can move a step nearer towards considering the simple relations between musical and poetic rhythm.
The technical terms of prosody are of no use here, with the solitary exception of the word anacrusis, which may be generalized to mean anything that happens before the first principal accent.
When Rockstro tells us that "the theme of Weber's Rondo brillante in E flat (op. 62) is in Anapaestic Tetrameter Brachy catalectic, very rigidly maintained," this tells us less about the music than Weber's brilliant theme tells us about these solemn terms. A more scientific idea of Weber's theme, and of the pro sodic technicalities, may be obtained from the following paradigm, to be recited prestissimo. Each dash at the end of the line repre
sents a quarter of a beat.
Prestissimo.
2. Time.—The body-rhythm underlying Weber's Rondo bril lante is an unchangeable binary rhythm, counted (as the paradigm shows) in a slow two or a quick four. Classical music uses only binary and ternary times, which, so long as vertebrate anatomy continues to develop with bilateral symmetry, are the only ones that yield a strong body-rhythm naturally, the elements of triple time giving just enough resistance to be overcome by a pleasant compromise. • The kinds of time, i.e., of invariable rhythmic molecules under lying each continuous piece of music, are classed not only as duple and triple but also as simple and compound. Compound time is the result of dividing simple time by three. Division by two is ignored : thus the evidently highly compound time of Ex. is reckoned as simple triple time. All beats are reckoned as binary divisions and subdivisions of the modern standard note, the semi breve : the time-signature given at the beginning of a composition is a fraction, with a numerator showing the number of beats in a bar, and a denominator showing the size of the beat. Thus / signifies three crotchets (quarters) in a bar. Compound time does not indicate the main beats at all, but counts the smaller beats as normal fractions of the semibreve. The main beats are written as dotted notes, in which the dot lengthens the note by one half.