Early 19th Century Brass Navigators Tool by William Carys, 1800

A navigator's scale rule, graduated in inches from -1 to 35, as well as ½" and ¼" (right to left).
Made from solid brass with etched graduations, it is heavy enough to hold a rolled blue-back chart flat on a table.
with its original wooden case.

William Cary (1759-1825), the youngest brother of mapmaker John Cary, served an apprenticeship with instrument-maker Jesse Ramsden before setting himself up in business c.1785 at 272 Strand.
In 1794 he moved to 182 Strand, next door to John, with whom he worked on the creation of globes, which were published by 'J. & W. Cary' at John's address of 181 Strand. After 1820, when both premises were completely destroyed by fire, John moved to St James's Street and William moved into the rebuilt 181 Stand.
In 1820 Cary was a charter of the newly-formed 'Astronomical Society of London', later the 'Royal Astronomical Society'.
After his death his business was taken over by John's sons, George and John.

William Cary's reputation was based on the precision of the instruments he made. Among his commissions were a transit instrument (a telescope with an extremely precisely graduated mount) for Napoleon Bonaparte and a three-foot theodolite for the Great Trigonometrical Survey of India under George Everest.