Clear-glass, mercury thermometer in original
blue velvet and silk lined black shagreen case.
The silvered scale is graduated from 0 to 100
degrees Fahrenheit and is engraved with the
maker’s name Troughton London and
made about 1790 by Edward Troughton
(1756-1835).
Length of plate 9 inches (23cms).
Ticket price £390.
Planimeters are used for measuring areas on a flat surface. This form, which uses polar coordinates,
was invented in 1854 by Professor Jacob Amsler (1823-1912), Professor of Mathematics at
Shaffhausen, Switzerland, where this example was made. Realizing the utility of his instrument, he
founded a factory for their manufacture.
Made of lacquered brass, the tracing arm can be extended and adjusted with a fine screw and has a
number of gauge points engraved on it, as well as the sellers name, STANLEY, GREAT
TURNSTILE, HOLBORN, LONDON. William Ford Stanley (1829-1909) founded his successful
instrument making business in 1853.
The radial arm is held in place by the original weight, which pushes a fine pin into the paper and is the
point around which the instrument rotates. The result is found by deducting the original figure indicated
on the electrum dial scale and vernier from the final figure. Electrum is a nickel based alloy and the dial
and scales were replaced about 1890 by white celluloid with black numerals. Later, the entire
instrument was made from a nickel based alloy.
