15 Capitals of Vaulting Shaft. 14 Tracery of Triforium. 13 Triforium-Arch. 12 Bases of T. Piers. 11 Capitals of do. 10 Pier of T. (Secondary). 9 do. (Primary). 8 Triforium String. GROUND-STORY. 7 Corbel. 6 Vaulting-Shaft. 5 Pier-Arch. 4 do. Band. 3 do. Base. 2 do. Capital. 1 Pier. [Illustration: EXTERIOR COMPARTMENT.] CLERE-STORY. 28 Parapet. 27 Cornice. 26 Clere-story Buttress. 25 Flying Buttress. 24 Tracery of C. Window. 23 Window Arch. 22 Mullions of C. Window. 21 Sill of do. 20 Jambs of do. 19 Weather Table. AISLE COMPARTMENT. 18 Aisle Roof. 17 Capping to Buttress. 16 Parapet. 15 Cornice. 14 Gurgoyle. 13 Canopied Set-off. 12 Plain Set-off. 11 Tracery. 10 Window Arch. 9 Mullion. 8 Sill. 7 Bases of Window Shafts. 6 Capitals of do. 5 Jambs. 4 Canopied Niche. 3 String-Course. 2 Buttress. 1 Base-Course. FOOTNOTES: [Footnote C: "Treatise on the Rise and Progress of Window Tracery." Van Voorst, London.] CHAPTER III. EXTERIOR AND INTERIOR COMPARTMENTS. The most perfect type of a church built in England, during the best ages of Church Architecture, may be said to contain the following essentials:-- 1. The Ground Plan is after the form of the Latin Cross, and is divisible _longitudinally_ into three portions; namely, THE CHOIR, THE TRANSEPTS, THE NAVE. 2. The Choir and the Nave, and occasionally the Transepts, are divided, by means of columns and arches, _transversely_ into three portions, consisting of the CENTRE AISLE, NORTH AISLE, SOUTH AISLE. 3. The MAIN WALL of each of the first-mentioned separate portions of the building is divisible, in the interior _vertically_ into three portions, or Stories, consisting of THE GROUND-STORY, THE TRIFORIUM OR BLIND-STORY, THE CLERE-STORY. Now on viewing any of these Main Walls of a building, whether on the inside, or the outside, it will be at once seen that they consist, in their entire length, of a series of single and separate portions, or _Compartments_, tied together, and connected by the horizontal lines, or String courses, which traverse them from end to end; and that each of these single Compartments embodies within itself the spirit of the whole design, and may be said to represent, individually, the MAIN IDEA of the Building. It is this portion of such a building then--a single Compartment of the Exterior and Interior of the Main Walls of the Choir or Nave, and its adjacent Aisle--that we have selected for the purpose of instituting that comparison which will enable us to fix and define the characteristics of the Seven Periods of English Architecture.