There is, then, a unit of time on which all verse-rhythms, like all musical rhythms, are based; and this is what we commonly call in music the _measure_, and in verse, the _foot_, I shall recur to this matter a little later in considering the terminology of the subject; for the present let us return to the relations of verse and music. Both, we have seen, are based on the recurrence of accented sounds at equal time-intervals. There is some difference, however, in the emphasis which one naturally places on the respective parts of the statement. In music we feel that the fact of chief importance is that the measures shall be equal in time, while the recurring accent seems a mere means of marking this equality; but in verse we feel that the chief fact is that the accents shall recur, the equality of time-intervals being in a sense a secondary source of pleasure. In music, therefore, as we have seen, we treat departures from regularity of time-intervals as somewhat more exceptional than in verse. But the rhythm would suffer, would even disappear, were either element wholly removed. If we look for further distinctions between verse and music, we find them in the separate sounds which go to make up the unit-measures. Not only are the measures of music of mathematically equal length, but all the sounds bear exact time-relations to each other: each is either half as long, or twice as long, or a quarter as long, or four times as long, as its neighbor. On the other hand, the number of separate sounds in the measure constantly varies; it is sufficient that the total length be that of the full measure. In verse these conditions are reversed. The separate syllables, while they doubtless vary in length, are not mathematically coördinated as to duration by the ordinary reader. It is almost as difficult to say just what the time-relation of any two adjacent syllables is, as to be sure that one is stressed just twice as strongly as the other. On the other hand, the _number_ of syllables in the foot (in good modern English verse) is tolerably constant. For the sake of completeness, one may add two other fundamental distinctions which, _apart_ from the elements of rhythm, differentiate verse from music. Music, apart from rhythm, characteristically depends on variation of pitch, and only incidentally (as in the case of the use of different instruments in orchestration) on variation of sound-quality; whereas verse, apart from rhythm, characteristically depends on variation of sound-quality,--that is, on the different sounds of the different words,--and only incidentally on changes of pitch. Finally, the changing sounds of music are only vaguely symbolic, while the changing sounds of verse are symbolic of definite ideas. For the sake of easy comparison we may put these observations in a rough sort of table: MUSIC VERSE _Rhythmical Sound_, i.e.