A transcript of Geoffrey Chaucer's treatise on the astrolabe, an instrument used for the taking of altitudes of heavenly bodies, from which time and latitude are deducible, entitled 'The dyscrypcion or knowelege of the astrolop ...' . On the cover is a verse by John Edwards, Chirk (see note under 'Tarddiad'), and who was probably the grandson of John ab Edward Hen, who owned NLW MS 423 (see under 'Associated Material' in the FONDS description).