See this legally free ebook:
- Gregorian Chant for Church and School, by Sister Mary Antonine Goodchild, O.P. (Boston, New York, Chicago, Atlanta, Dallas, Columbus, San Francisco, Toronto, London: Ginn and Company, 1914). With Imprimatur. Available in PDF format (144 pages) on this page of the Church Music Association of America.
“I saw the Lord sitting on a throne that towered high above me, the skirts of his robe filling the temple. Above it rose the figures of the seraphim… And ever the same cry passed between them, Holy, holy, holy is the Lord God of hosts; all the earth is full of his glory. The lintels over the doors rang with the sound of that cry, and smoke went up, filling the temple courts.” (Isaiah 6:1-4)