One of a set of three of the largest slates recorded, dated 1837. The originals are still in situ. The source of the astronomical data was John William Thomas (Arfonwyson) 1805-1840. Born at Rallt, Pentir, Arfonwyson was a mathematical genius whose astronomical drawings brought hum to the attention of the Astronomer Royal and led to his appointment at Greenwhich Observatory
Afonwyson gave a collection of astronomical information and patterns to his friends, Richard and Grace Jones, Bryn Twrw. These patterns were used by Grace’s brothers Thomas and William Jones, quarrymen and farmers on these detailed carvings.