A ship's navigator could find latitude from the sun. Longitude was harder: it depended on knowing the exact time at home while far out at sea. The marine chronometer made that possible, and only if it kept its rate through heat, cold and weeks of motion.
The trials
The Royal Observatory at Greenwich tested chronometers every year before the Admiralty bought them. Instruments were run for months and their daily rates recorded, through changes in temperature that would expose any weakness in the balance.
The flat-rim balance
Victor Kullberg entered the trials regularly from his workshop in Islington. In 1864 he took first place with a chronometer fitted with a new balance of his own design, the flat-rim balance. The balance is the part that keeps time; a compensation balance changes shape with temperature so that the rate does not.
In service
Kullberg supplied more than 500 chronometers to the Royal Navy. One deck watch signed by the firm, number 8333, was bought by the Admiralty in 1916 and stayed in Navy service until 1965. It is now held by Royal Museums Greenwich.
