Prismatic Surveying Compass by Stanley for The Geological Survey c1920 – SOLD
Prismatic surveying compass having 3” engine divided polished and engraved compass ring with cross bar indicating ‘N,’ graduated in degrees with 0 degrees set at south, jewelled suspension, maintained in a drum form case. Convex-faced 45 degree two-position reflecting prism with height (focus) adjustment having rotating lens cover, red and green solar shades. Folding sighting vane (stowed position arresting the circle), fine wire sight, sliding and tilting reflecting mirror.
The verso with ½” mounting point. Push fit lid, engraved with the crown and ‘G S’ Geological Survey logo, signed by the maker “Stanley, London,” and marked “British Made.”
Together with its original tan leather and maroon velvet lined baton case with strap and buckle secured crescent lid. Maker’s label in gold block to inner lid with Stanley’s 286 High Holborn, London address and trade mark. Case marked internally by hand, “Stanley, GS.”
Original condition with few signs of use, the compass swings freely, easily finding north. Minor losses and abrasions to lacquered finish, the leather case with some marks and impressions, losses to leather over buckle.
The surveyor’s compass evolved as a specialised type of ‘bearing compass’ in the early 17th century and was commonly in use for surveying large-scale civil engineering works such as canals, roads and water supply by the early 18th century. The railway construction boom of the 19th century further expanded its use and helped stimulate numerous design improvements, including improved portability with smaller and lighter instruments that could be carried and operated in one hand. Following Charles Schmalcalder’s design and patent of the prismatic compass in 1812, the first specific prismatic surveyor’s compass design was patented in 1885, incorporating a viewing prism and lens attachment that enabled the user to more accurately sight the heading of geographical landmarks or an alignment when laying out the route of roads, railways, canals or aqueducts.
These instruments are seldom seen – far less in this condition. Very much a collector’s piece.
Dimensions: 5¼” long x 4″ wide x 2″ deep (case)
Stock No: SI0540