About Cantus Organi

The organ accompaniment of the Graduale, for the Traditional Latin Mass and Vespers, at the console.

What it is for

Nova Organi Harmonia ad Graduale Romanum was published by the Lemmens Institute at Mechelen in 1942: eight volumes of organ accompaniment for the whole of the Gregorian repertoire of the Mass and of Sunday Vespers. It is in the public domain, but in print it is rare and scattered, and finding the right page for a given Sunday means knowing which volume holds it.

This site puts the scanned pages online, divided into 455 pieces, and ties them to the calendar of the 1962 Missal, so an organist can go from a date to the music for that day's Mass and Vespers. Nothing is re-engraved: every system of music is an image of the printed page, with its printed page number.

How to use it

Find the music for a day

Open the Calendar and choose a date. The day's page lists the Proper of the Mass (Introit, Gradual, Alleluia or Tract, Offertory, Communion), the Ordinary it suggests, and its Vespers. Each part has a link straight to its place in the music.

Vespers

For Sundays and feasts, the Vespers pages give the whole office in the order sung — the opening versicle, the five psalms with their antiphons, the chapter, hymn, versicle, Magnificat and the seasonal Marian antiphon — built for each date from 2025 to 2031. I Vespers of the greater feasts have their own page, for the evening before. Where the book prints only the opening of a psalm, the page says which formula to continue with and gives the psalm's text; where it prints no accompaniment in a tone at all, the page says so rather than guess.

Browse the books

The home page lists the books as printed: the Proper of Time, the Proper of Saints, the Common, the Kyriale, the Masses for the Dead, the Vesperale, and votive Masses. Search finds a piece by its title or opening words.

At the organ

Invert (top of every page) turns the scans white on black, for a dark organ loft. The setting is remembered on that device.
Export PDF makes a file of the pages you need, to print or to keep on a tablet on the music desk.
Chant links open the melody on GregoBase; on pages that offer it, the switch Show the chant draws the chant above the accompaniment.
Pages print cleanly: the menus and buttons are left off the paper.

What it does not do yet

Only the 1962 rubrics. Earlier and later calendars are not followed.
Vespers is built for Sundays and I and II class feasts that the book prints. A few feasts that fall on a Sunday only in some years (the Transfiguration, the Holy Cross, St Michael) have no Vespers page, because the book has no section for them.
Some Magnificat and psalm tones are not printed in the Vesperale; those are marked on the page to be sung unaccompanied or improvised.
Parts of the catalogue were matched by machine and have not all been checked by eye.

Errors and corrections

If a piece is on the wrong page, a title or mode is wrong, or a chant link points at the wrong melody, please say so on the Corrections page. Every report is read and fixed by hand.

Sources and attributions

Nova Organi Harmonia ad Graduale Romanum: Lemmens Institute, Mechelen: H. Dessain, 1942. The page images and everything cut from them are in the public domain.
GregoBase: The chant melodies shown with each part and linked from it. Released under CC0.
Exsurge: Draws the chant notation in the browser. MIT licence, © 2016 Fr. Matthew Spencer, OSJ; maintained by Benjamin Bloomfield.
jgabc: Which chants make up each day's Proper. The Unlicense (public domain).
Missalemeum: The 1962 calendar: which Mass is said on each date. MIT licence.
Divinum Officium: The texts of Vespers — antiphons, psalms, chapters and hymns — and which are said on each day. MIT licence.
vesperale: Fr. John Jenkins's Vespers booklets, whose table of Magnificat antiphons and tones was used to check this site's.
Pagefind: The site search. MIT licence.

The site itself, its code and its hand-made indexes of the books are released under CC BY-SA 4.0, and are on GitHub, so the work can be copied and carried on.