A grammar of Welsh Poetry by David Thomas (Dafydd Ddu Eryri) entitled Cyfrinach y Beirdd wedi ei ddwyn i'r amlwg : neu Reolau Prydyddiaeth Gymraeg. Dafydd Ddu appears to have circulated copies of this work among the Welsh bards with the object of obtaining their criticism thereon before publication (p. 4). The manuscript also contains a Welsh grammar said to be written by William Jones of Llangadfan (1726-1795), and a religious song of anonymous provenance.