There are considerable difficulties attendant on an attempt to assign a precise date to the addition of an octave to this festival; and the festal character of the octave week was affected by the ember days occurring in that week. In the Gelasian Sacramentary, as it has come down to us, we have the ‘propers’ for a mass on the Sunday of the octave of Pentecost. The mass may be described as a mass of the Holy Spirit, praying for protection for the Church from the allurements of the vain and deceitful philosophy of the world; true knowledge of the nature of God was given by the bestowal of the Holy Spirit, the Spirit of wisdom, and knowledge, and understanding, and counsel. The benedictions, which immediately follow, on those who return to the Catholic unity from the Arian and other heresies, suggest that it was in this way that the octave of Pentecost came at a later date to be made a festival in honour of the mystery of the blessed Trinity[73]. The public reception to the Catholic unity of Arian and other heretics would gradually cease to be a feature of the season: but the liturgical colouring of the service would remain, and would have to be accounted for. As a matter of fact, however, the establishment of a festival of the Trinity with a special office and mass was of late date. It makes its appearance in the Low Countries in the tenth century, and made its way but slowly, and with varying success. Pope Alexander II, who died in A.D. 1073, when consulted on the subject, wrote that according to the Roman rite there was no day set apart to commemorate the Trinity any more than the Unity of the Divine Being, and that every day of the year was truly consecrated to the honour of the Trinity in Unity. It was not till the fourteenth century, under the pontificate of John XXII, that the Roman Church received the feast of the Trinity and attached it to the first Sunday after Pentecost[74]. In England, according to Gervase of Canterbury, Archbishop Thomas Becket instituted the principal feast of the Trinity on the octave of Pentecost[75]. CHAPTER V FESTIVALS OF ST MARY THE VIRGIN I. _Western Kalendars._