I once read in a book some time ago, and the book was old then, of a list of days called 'Days of Observance'. It was a list of days which the clergy were mandated to observe by celebrating Mass. But, they were not days on which the laity should go to Mass. Obviously, it was some concept of Anglo-Catholicism because I do not think the Church of England has any days on which celebration of the Eucharist is compulsory for clergy or laity. Has anybody else ever encountered these days of obligation? If you have do you know which days are on the list?