*Ad regias Agni dapes. The Roman Breviary version of the Ambrosian Ad coenam Agni providi, above. It is the hymn at Vespers, "Sabbato in Albis," i.e. on Saturday in Easter-week, and afterwards on Sundays and week-days, when no Festival occurs and the Ferial Office is said, till the first Vespers of the Ascension. In addition to the ordinary editions of the Roman Breviary the text is given in several modern Roman Catholic hymnals, Card. Newman's Hymni Eccl., 1838-65; Biggs's Annotated edition of Hymns Ancient & Modern, 1867; Daniel, i. No 81, &c. [Rev. W. A. Shouts, B. D.]
Translation in common use:—
We keep the Festival. By A. R. Thompson, contributed to Schaff’s Christ in Song, 1869.
-- John Julian, Dictionary of Hymnology (1907)