It will be seen that the semi-tones are immovable, and therefore occur in different positions in each mode, by the change of the key-note; being respectively,— First mode, semitones 2-3, 6-7 Second ” ” 1-2, 5-6 Third ” ” 4-5, 7-8 Fourth ” ” 3-4, 6-7 It was this distinction which gave to each mode its peculiar character. Not only did St. Ambrose reinstate these modes, but he composed many beautiful compositions in them. Many of the so-called Ambrosian chants and hymns, were not written by him, but after his manner; but some ten of the ancient hymns, including “_Veni Redemptor Gentium_,” “_Eterna Christi munera_,” etc., are from his own pen. The Cathedral of Milan still uses _Aeterne rerum conditor_; _Deus Creator omnium_; _Veni Redemptor omnium_; _Splendor Paternæ gloriæ_; _Consors paterni luminis_; and _O Lux Beata Trinitas_.[252] Some of these are of rare beauty, and remain as monuments of the cultivated taste of this pioneer in church music. The composition of the “_Te Deum Laudamus_,” has been ascribed to St. Ambrose, and St. Augustine; but it was composed nearly a century after their death. Among other persons to whom this beautiful production has been assigned, may be mentioned St. Hilary, St. Abundius, St. Sisebut, and St. Nicat; but it may be safely affirmed that its real author has never been discovered. The greatest boon bestowed on the church by St. Ambrose was the rhythmical hymn, mentioned above, all of which, and many others he wrote for the Cathedral which he built at Milan. “The entire accent, and style of chanting as regulated by him, was undoubtedly an artistic and cultivated improvement on that of preceding church services, such as would naturally result from the rare combination of piety, zeal, intellect, and poetical and musical power by which he was distinguished.” The Ambrosian chant was eventually merged, but certainly not lost in that vast repertory of plain song, (whether then ancient or modern,) which we now call Gregorian, from the name of the next great reformer of church music, St. Gregory the Great.[253] St. Ambrose died A. D. 397; it was but a short time afterwards that the great invasion of the northern barbarians took place. The history of the vicissitudes of the ecclesiastical music, during the general disruption of Europe and the western civilization, which followed, can only be imagined; but scarcely had a calm been re-established, when, at a period when the reforms and inventions of St. Ambrose had not been vitiated or lost, the great reformer of church music arose, and re-instated the art upon a firmer pedestal than ever.