Just as single tones are grouped together rhythmically to form a measure, successions of measures are grouped rhythmically, in the construction of musical form. The rhythm of most classical forms is in twos, fours, eights, etc.; a group of eight measures ending with a half-cadence, or part question, answered by a similar eight measures ending on a full cadence, or definite conclusion, is a familiar method of building; and often a second section will contain a new theme in contrast to the theme in the first section, and the first section will be repeated in some form to close. Since some of the links formed by metrical harmonies are long, it would be interesting to consider such a link as a definite new form into which suitable musical material could be poured. Such a form would make for perfection of outline, and it would give a clarity and purpose to the composition as a whole, which are often lacking in works using experimental material. It would be found that the type of metrical combinations near the centre of the great link would be a contrast to those at the beginning, so that the principle of a contrasting middle section would be suggested; and that the smaller links in the latter half of the great link would be an exact reverse of the first part, so that there would be a recapitulation of the first theme, in reverse, at the close. Other ways of varying metre might be also applied to musical form. It would be interesting to investigate possibilities of irregular sections. Numerous classical composers have written occasional irregular sections, usually with such skill that the average listener is unaware that unusual rhythm has been employed. Much contemporary composition contains irregular sections, or an odd number of measures in a section, but it is not customary to sustain a certain scheme of form throughout a composition.