As Eos awakened, clothed in shining whiteness, to see another day of cloudless skies. It is the Octave of the Assumption of the Most Holy Mother of God, the Blessed Virgin Mary; in the more recent Kalendar today is celebrated as the feast of her Immaculate Heart. The Mass is Adeamus cum fiducia ad thronum gratiae. But I will be interested to see if the celebrant at Saint-Eugène says this Mass or Signum magnum.
M. Grodziski is indeed saying the Adeamus.
Adeamus cum fiducia ad thronum gratiae, ut misericórdiam consequámur, et grátiam inveniámus in auxílio opportúno.
Alleluia, alleluia. Magnificat anima mea Dominum: et exsultavit spiritus meus in Deo salutari meo, alleluia.