Description and Notes:
This brass pantograph is dated to the first half of the 19th century as the maker, W. & S. Jones, were working at 30 Holborn, London, from 1800 to 1860. It comes with a solid mahogany case and complete with cupped pencil holder and tracing point.
Three of the lacquered brass bars to place the fulcrum, the tracer, and the pencil holder are respectively marked as B, C, and D at one end. The length of the two longer bars (B and C) is 28 inches. This instrument is capable to perform reduction from 1:2 to 1:12, as indicated by the scales engraved on bars B and D. When set up, the pencil holder and the tracing point are connected by a cable through two rings and a pulley attached to the junction points of the bars, such that the pencil holder can be raised by pulling the cable from the tracing point end at any instance regardless the configuration of the mechanism.
Overall, the material and construction of this pantograph is consistent with the design of the ones produced in the early 19th century, a similar one by the same maker can be found in page 132 of Drawing Instruments 1580-1980, but the wheels of the six castors of the presented one are made of ivory instead of porcelain and are unusually large in size (about one inch in diameter).
Detailed operation of a pantograph can be found in W. F. Stanley's A Descriptive Treatise on Mathematical Drawing Instruments, Chapter XVIII, pp. 110-120.