The reader will understand that every scale was divided into two tetrachords, each having its semitone in the same position. There were, of course, several other scales, but these are sufficient to illustrate the subject. The peculiarity of the sound of chants founded on these ancient scales to our modern ears is what we call the "lack of tonality." Our scales are all determined by the semitone between the seventh and eighth notes, called the leading note. The scale of G, for instance, cannot exist without the F sharp. Our ears have been trained to expect that progression, and so these old Greek scales do not seem to us to be in any key at all, and when we wish to describe a tune that has apparently no beginning, end, or rhythm, we say it sounds like a chant. For several centuries all modern music written by the scientific composers suffered from this lack of tonality, while much of the popular music of the people was written in the modern major and minor keys. Any musician will see that the old Lydian scale was our scale of C major. The ancient Æolian scale was almost the same as our scale of A minor. From these two our modern scales developed themselves among the people who were not busy trying to build church liturgies out of Greek music. Not much is known about the musical character of the Ambrosian chant except that contemporary writers regarded it as very sweet and solemn. One important fact has come down to us, namely, that the Ambrosian chant was metrical. This means that it followed the prosodial quantity of the syllables in the Latin text of the liturgy. A long syllable had a long note, and a short syllable a short note. From this peculiarity the chant obtained the name of _cantus firmus_, or fixed chant. It was, however, speedily merged in what is called the Gregorian chant. This has generally been attributed to Pope Gregory (590-604 A. D.); but recent investigations go to prove that he did little beyond issuing rules as to its use and for its regulation. The church chant, however, was changed in character in the time of Gregory, and one of the most fruitful alterations was the abandonment of its metrical character. The tones no longer had a determined length; and this abolished from the church music of the time the last vestige of rhythm. It furthermore left the singers free to do as they pleased, and so gave rise to abuses which seemed to be injurious to music, but which really led to good results, as we shall see. In form, the Gregorian chant was divided into five parts: the "intonation," which was the introductory phrase of the first half of the verse; the "recitation" of the principal part of that half on a single note; the "mediation," which finished the first half of the verse and formed the connecting link between it and the second half; the "recitation," which began the second half; and the "termination," which ended the verse.