The daily hymn for None in the Roman Breviary
Rerum Deus Tenax Vigor, the daily hymn for None in the Roman Breviary, comprises (like the hymns for Terce and Sext) only two stanzas of iambic dimeters together with a doxology varying according to the feast or season. As in the hymns for Prime, Sext, and Compline, the theme is found in the steady march of the sun that defines the periods of the day:
Rerum, Deus, tenax vigor
Immotus in to permanens,
Lucis diurnae tempora
O God, whose power unmoved the whole
Of Nature's vastness doth control,
Who mark'st the day hours as they run
By steady marches of the sun.
The moral application is, as usual, made in the following stanza:
Largire lumen vespere
Quo vita nusquam decidat, etc.
O grant that in life's eventide
Thy light may e'er with us abide, etc.
The authorship of the hymns for Terce, Sext, and None is now ascribed only very doubtfully to St. Ambrose. They are not given to the saint by the Benedictine editors (see Ambrosian Hymnography), but are placed by Biraghi amongst his inni sinceri, since they are found in all the MSS. of the churches of Milan. Daniel (I, 23; IV, 13, 17) thinks that much longer hymns for the hours were replaced by the present ones. Pimont disagrees with Daniel and argues that the saint may well have composed two sets of hymns for the hours. However, the researches of Blume (1908) show that the primitive Benedictine cycle of hymns, as attested by the Rules of Caesarius and Aurelian of Arles, did not include these hymns, but assigned for Terce, Sext, and None (for Easter-tide) the hymns: "Jam surgit hora tertia", "Jam sexta sensim volvitur", "Ter hora trina volvitur"; the earliest MSS. of the cycle give for these hours, for the remainder of the year, the hymns: "Certum tenentes ordinem", "Dicamus laudes Domino", "Perfectum trinum numerum"; while other MSS. give as variants for Lent: "Dei fide qua vivimus", "Meridie orandum est", "Sic ter quaternis trahitur". This Benedictine cycle was replaced throughout Western Christendom by a later one, as shown by Irish and English MSS., which give the present hymns for the little hours.