7 plates from Col Sir Henry James, Extension of the Triangulation of the Ordnance Survey into France and Belgium ..., 1863: cross-channel triangulation map, 16.5 miles to an inch, with northward continuation diagram, 58 miles to an inch; sketch diagrams,10 feet to an inch; observatory signals used at ground stations; scaffolds used at Gravelines, Dunkirk, Cassel and Harlettes (2)