During an inquiry into the Theory of Equilibration of Arches, I had occasion to take sections of those buildings in this country most remarkable for the arcuation in them; and circumstances induced me to select Trinity Church Ely, King's College Chapel Cambridge, Westminster Abbey, Ely, Lincoln, York, and Peterborough Cathedrals. The three sections, viz. of St. Paul's Cathedral, of the Temple Church, and of Henry the Vllth's Chapel, which I have sent with this, (Pl. XXI. XXII. XXIII.) were made at a subsequent period, when I was engaged in the inquiry into the different forms of vaults, which led to the Observations published in the seventeenth volume of the Archaeologia.