A few weeks ago I had occasion to mention the Roman Gradual. The Monks of Solesmes are responsible for the modern edition. For various technical reasons [insert flannel] to do with new discoveries in the correct interpretation of the notation of plainchant, they also produce the same book with the neumes (the signs) from the earliest manuscripts added. This is called the Graduale Triplex – because it records the notation of the manuscripts of Laon, St Gall and Einsiedeln. The introit for the Mass of Christmas during the Day looks like this:
(Credit to: Karen Thöle of Mittelalter-Recherche).
But, you know, sometimes I find the Graduale Triplex just doesn't tell me enough.
On those days I swiftly repair to Charles Cole's post of a list of Semiological Sources. There are links to online facsimiles of all the major chant manuscripts. God bless the internet, and all who sail in her.