This song presents a further element of form by means of which much variety is imparted to music.

III. KEY AND MODULATION.

It will be noticed that the first phrase of "Polly Oliver" (measures 1-5) moves about the tone E-flat and ends upon it with the effect of coming to rest, and that the second phrase (measures 5-9) similarly moves about and comes to rest on the tone B-flat. The last phrase (13-17), like the first, moves about E-flat. This moving about a certain tone, which is, so to speak, the center of gravity of the whole phrase, is called by musicians "being in the key of" that tone; and when the center of gravity changes, musicians say that the piece "modulates" from one key to another. Thus, this first phrase is in the key of E-flat, the second modulates to the key of B-flat, and the song later modulates back again to the key of E-flat. Here we have another very important principle in modern music, the principle of "key" or "tonality,"—important because it makes possible a great deal of variety that still does not interfere with unity. By putting the first part of a piece in one key, the second part in another, and finally the last part in the original key, we can get much diversity of effect, and at the same time end with the same impression with which we began. We shall only gradually appreciate the immense value to the musician of this arrangement of keys.

A further element of form is found in "Polly Oliver," namely, the balance of phrases. This balance of phrases one against another is derived ultimately from the timed motions of the body in dancing, or from the meter of the four line verse to which the music was sung. And this balance of phrases, derived from these elemental sources, still dominates in the melodies of the great masters, although it is managed with constantly increasing freedom and elasticity, so that we find in modern music little of that sing-song mechanical regularity which we may note in most folk-songs and dances.

IV. BARBARA ALLEN.

Let us now examine another old English song, "Barbara Allen."

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FIGURE VI.

In Scar-let Town where I was born,