Brass proportional divider
- Author: CARY, William
- Publication place: London
- Publisher: Cary
- Publication date: c1790-1810
- Physical description: Six-inch proportional dividers, brass body, steel point, with engraved units on both sides.
- Inventory reference: 15966
Among the instruments manufactured by Cary were a selection of navigational tools including proportional dividers. This instrument, also known as a sector or a reduction compass, consists of two branches locked together at a changeable fixed point on a scale. The distance between the two points can be used to calculate and compare distances, and proved particularly useful for the enlarging or reducing of a map’s scale.
The present proportional divider has four scales with distinct ratios, one engraved on either side of each branch: circles (1:6 to 1:20), lines (1:1 to 1:10), plans (1:1 to 1:10) and solids (1:1 to 1:10). Each scale is labelled, and the maker’s name and location are also identified towards the top of the instrument. The engraving remains exceptionally clear, and may be the work of another Cary brother, Francis.
The present instrument is extremely rare. We have been able to trace only one other example, in the private collection of mathematical instruments of David M Riches. While the Andrew Alpern Collection of Drawing Instruments at Columbia University contains several tools produced by Cary, a brass proportional divider is not among them.