Arcograph
An instrument sometimes used by watchmakers for drawing a circular arc without the use of a central point.
ARNOLD, JOHN. Born in Cornwall, England, in 1744, and died at Eltham, England, in 1799. He was the inventor of the helical form of balance spring and a chronometer escapement. The English Government awarded him pound1,320 for the superiority of his chronometers in 1799, and his son, who followed up the successes of his father, was awarded pound1,680 in 1805.