Apologies to readers for not posting anything on St. Matthias' Day on Ember Wednesday but I was out of town.
When a double of the first class or double of the second class falls on an Ember Day in Lent then the Ember Day is commemorated at Lauds and Mass. The Office and all Masses are of the feast. So on Wednesday the Office was of St. Matthias. At Mattins the ninth lesson was the homily of the Ember Wednesday and a commemoration of the Ember Wednesday was sung at Lauds. At Mass the second collect was of the Ember Wednesday and its Gospel was read as a proper last Gospel.
Ember Friday is a ferial day so the Office of the Ember Day is celebrated in its entirety. The Office of an Ember Day begins with Mattins (like any other ferial day). The invitatory is Non sit vobis and the hymn Ex more docti mystico. The nine antiphons of the ferial nocturn are sung. The lessons are a homily from St. Augustine on St. John's Gospel. At Lauds the second schema is sung with the antiphons of the ferial psalter. After the antiphon on the Benedictus is sung the ferial preces are chanted, the choir kneeling. The Suffrage of the Saints is sung.
At Prime the psalm displaced from Lauds by the Miserere is added to the day's psalmody so Pss 21(i), 21(ii), 21(iii) & 98 are sung. The chapter is the ferial Pacem et veritatem and both the Dominical and ferial preces are sung, kneeling. At the Hours the short set of ferial preces are sung, again kneeling.
The Ember Friday Mass is sung after None. The ministers wear folded chasubles as at any other Mass of the season in Lent. The Gloria is not sung. The second collect is A cunctis nos, the third Omnipotens. The preface is of Lent and Benedicamus Domino is sung as the dismissal.
Vespers are of the following feast of St. Gabriel of the Seven Dolours. A commemoration of the Lenten feria is sung. At Compline the Dominical preces are omitted.
On Saturday the Office is of the double feast of St. Gabriel. At Mattins the lessons in first nocturn are Justus si morte taken from the second place in the Common of Confessors. The ninth lesson is homily from the Ember Saturday. At Lauds the Ember Saturday is commemorated.
Private Masses may be of the feast or of the Ember Saturday. In Masses of the feast the Gloria is sung, the second collect is of Ember Saturday (the prayer Populum tuum found after the Kyrie in the texts of Ember Saturday). The preface is of Lent, the dismissal Ite, missa est and the last Gospel of the Ember Saturday. If the Ember Saturday Mass is celebrated violet vestments are worn (with the deacon and subdeacon wearing folded chasubles). The Mass has the usual, ancient form, for Ember Saturdays. After the Kyrie there are a series of structural units comprising of the invitation Oremus, followed by Flectamus genua, Levate, a collect, O.T. reading and gradual. The first and second OT readings are from the Book of Deuteronomy. The third lesson is from Machabbees, the fourth from the Book of Wisdom. The fifth is from the Prophet Daniel describing the LORD protecting Azarias and his two companions in the Babylonian fiery furnace. After the reading from Daniel instead of a gradual the hymn of the Three Men in fiery furnace is sung, Benedictus es, Domine, Deus patrum nostrorum and its collect Deus, qui tribus pueris. The feast of St. Gabriel is then commemorated. The preface is of Lent and the dismissal Benedicamus Domino.
In Cathedral and Collegiate Churches two Masses are celebrated. The Mass of St. Gabriel is celebrated after Terce without any commemorations. The Mass of the Ember Saturday is sung after None with the second collect (before the Epistle) A cunctis and the third collect Omnipotens. The dismissal is Benedicamus Domino .
Vespers are of the following Sunday with a commemoration of St. Gabriel. The Dominical preces are omitted at Compline.
In the 'liturgical books of 1962' on Ember Friday the Suffrage is not sung at Lauds. At Prime there is no fourth psalm, the festal Regi saeculorum is the chapter, Pacem is supressed. The ferial preces are not sung at the Hours. At Mass (sung after Terce) there is only one collect and the dismissal is Ite, missa est. Vespers are ferial without a commemoration of St. Gabriel.
On Saturday the Office is of the Ember Day. At Lauds the Canticle of Moses is cut down from 65 to 27 verses. A commemoration of St. Gabriel is made at Lauds. The ferial preces are sung at Lauds but not at the Hours. At Prime there is no fourth psalm, the festal Regi saeculorum is chapter, Pacem is supressed. At Mass a 'mini-Ember Day' may be celebrated missing out most of the lessons that characterised Ember Saturdays. The dismissal is Ite, missa est. At Vespers there are no commemorations.