(Born 1799, died 1867)

A chronometer maker who devised many different forms of compensation balances.

(Born in Cornwall, 1736; died at Well Hall near Eltham, Kent, in 1799)

He invented the helical form of balance spring (Patent No. 1113, Dec 1775), and devised a chronometer excapement (Patent No. 1328, May 1782) very closely resembling the one by Earnshaw, which is now in use. In Arnold’s Escapement, the escape wheel teeth, instead of being flat where they gave impulse, were epicycloidal curves; but they required oiling, and were consequently abandoned. While Earnshaw’s wheel is locked on the points of the teeth and the detent moves away from the centre of the wheel to unlock, Arnold’s locked on the heel of the tooth and the detent moved toward the centre of the wheel to unlock, the sunk part of the body of the wheel allowing the locking stone to pass. His business was, after his death, carried on at 84, Strand, by his son John R. Arnold.

From Wikipedia, the free encyclopedia

John Arnold (born 1736 in Bodmin, Cornwall; died 1799 in London) was a watchmaker who developed and patented escapement and balance spring designs. He is known to have lived for a period at Well Hall House in Eltham, southeast London. In 1736, Arnold constructed what was then the smallest repeating watch, which was set in a ring and given to George III.

He then turned his attention to the production of ever more precise chronometers. One of these travelled with the explorer James Cook during his second voyage to the southern Pacific Ocean in 1772–1775. His undoubted claim to fame in the field of marine chronometers is the first application of a helical balance spring. This allowed the balance to swing through larger or smaller arcs in a constant time, one of the fundamental requirements for accurate timekeeping.

Arnold set up a small factory in Chigwell, Essex for the production of chronometers and in 1788 produced the first pocket chronometer. This watch, “No. 1/36″, greatly impressed the Astronomer Royal Nevil Maskelyne and was the first watch Arnold deemed worthy of the description “chronometer”.