C.S. Lewis, in a letter to Arthur Greeves (January 9, 1930), describes the pleasure of reading a commentary on Chaucer:
What a glory-hole is the commentary of an old author. One minute you are puzzling out a quotation from a French medieval romance: the next, you are being carried back to Plato: then a scrap of medieval law: then something about geomancy: and manuscripts, and the signs of the Zodiac, and a modern proverb 'reported to Mr Snooks to be common in Derbyshire', and the precession of the equinoxes, and an Arabian optician (born at Balk in 1030), five smoking room stories, the origins of the doctrine of immaculate conception, and why St Cecilia is the patroness of organists. So one is swept from East to West, and from century to century, equally immersed in each oddity as it comes up.
A glory-hole is "an opening in the wall of a glass furnace, exposing the brilliant white light of the interior" (Webster's Unabridged Dictionary
, 1913), used by a glassmaker to reheat glass.