Abstract
Acta Unitatis Fratrum represent an important source not only for general and ecclesiastical history, but also for hymnology. There are several important writings for research of the singing of the Unity of the Brethren.
The most important of them is the Index of the authors of the songs contained in the Szamotuly cantional from 1561. In connection with the Index, the defense of the theological purity of the cantional was probably created in response to Martin Žatecký's writings (Apologia pro editione cantionalis nova).
Both of these texts were included in the ninth volume of the Acta (ff. 318r-341r, 368r-392v). The former has been examined and edited several times in the past, the letter is receiving research attention just now.
To explore the use of songs and chants in the worship of the Unity of the Brethren, Blahoslav's Assiduous Meditation (Pilné rozjímaní) is important. It is also included in the ninth volume the Acta (ff. 64r-101r).
There is still another collection of documents on the history of hymnography organized by Jan Blahoslav in the seventh volume of the Acta (ff. 214r-252v). These are materials relating to a judicial proceeding with the printer Václav Oustský, who has been operating since 1544 in Mladá Boleslav.
The controversy took place in 1548-49 and concerned a hymnbook (today lost), whose planned appearance has changed several times. A contract was concluded in 1546 and the hymnbook was then fully prepared for printing.
During binding and distribution, however, there influential political events took place, and the whole project ended at the appellate court. In my chapter, I want to show the link between Oustský's activities and the Unity of the Brethren, and explain why the hymnbook belongs to a number of other unrealized plans associated with the bishop Jan Augusta.
I also point out what facts Jan Blahoslav stresses in the Acta and which he tries to overthrow. As a comparative material, a newly discovered record of the appellate court is used.
It is a manuscript held in the Prague City Archives under the shelf mark 323.