Ship's Chronometer


A chronometer is a precise clock used to find longitude at sea. The term chronometer (based on the Greek words “chronos” (meaning time) and “meter” (meaning counter) was coined in 1714 by Jeremy Thacker, an 18th century writer and watchmaker.

In 1714, during Queen Anne’s reign, the British Parliament motivated inventors to solve the problem of accurately calculating longitude at sea by offering awards through the Longitude Act. Jeremy Thacker was an early competitor for the prize money, which ranged from £10,000 to £20,000 (£2 million to £4 million in 2015 terms) depending on accuracy. During a 114 year time period, many awards were paid. An inventor named John Harrison received several awards from the 1730's to the 1750's. In 1765 he received £10,000. Harrison was voted 39th on a list of 100 Greatest Britons in a recent poll conducted by the BBC in 2002 for his work inventing the chronometer.

The creation of a timepiece which would work reliably at sea was an exciting advancement that was critical for accurate navigation, and in particular, for calculating longitude. Latitude could be determined by measuring the sun’s angle at noon. But calculating longitude was impossible when sailors were at open sea with no visible land, and thus accurate navigation was challenging before chronometer use was adopted in the mid-1750's. Until then, pendulum clocks were the best timekeepers, but the rolling motion of ships on the ocean prevented pendulum clocks from being useful at sea. Knowing GMT at local noon allows a sailor to use the time difference between the ship's position and the Greenwich Meridian to determine the ship's longitude.

With accurate navigation, British sailors were able to accomplish feats that were previously unimaginable. The success of the Royal Navy allowed the British Empire to expand through war and colony conquest thanks to their secret weapon, the chronometer, which their Portuguese, Dutch, and French opponents lacked. For example, the French were well established in India and other places before Britain, but during the Seven Years’ War, which took place mainly from 1756 to 1763, the British claimed some of their territory.

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