«RERUM DEUS TENAX VIGOR» — Hymn for the Hour of Nones, corresponding to three in the afternoon, attributed with less than full certainty to St Ambrose (cf. G. M. Dreves - C. Blume, *Anal. hymnica*, L, Leipzig 1907, p. 19). According to manuscript tradition it would belong to the Irish-Anglo-Saxon group (ibid., LI, Leipzig 1908, p. XX ff.).
At this hour the Church once more raises its voice in praise and prayer to the Lord, asking Him that as the light of day fades there may draw near the light in which the soul may immerse itself, without seeing the setting sun, in eternal glory.
Bibl.: G. S. Piment, *Les hymnes du Bréviaire romain*, I, Paris 1874, p. 76; F. Vandersyf, *Les hymnes du Bréviaire romain*, Paris 1912, p. 42.