History of the Marine Chronometer

Until the mid 1750s, navigation at sea was an unsolved problem due to the difficulty in calculating longitudinal (east/west) position. Navigators could determine their latitude (north/south) position by measuring the sun's angle at noon (i.e., when it reached its highest point in the sky, or culmination). To find their longitude, however, they needed a portable time standard that would work aboard a ship. Observation of celestial, "clockwork" motions such as Galileo's method based on observing Jupiter's natural satellites was usually not possible aboard due to the ship's motion. The Lunar Distance Method, initially proposed by Johannes Werner in 1514, was developed in parallel with the marine chronometer.

The purpose of a chronometer is to keep the time of a known fixed location, for example Greenwich, England, which can subsequently serve as a reference point for determining the ship's position. By comparing local high noon to the chronometer's time, a navigator could use the time difference between the two locations to determine the ship's present longitude. Since the Earth rotates 360 degrees every day (that is, 24 hours or 1,440 minutes), the time difference between the chronometer and the ship's local time indicated how many degrees of longitude separated them. With the degrees of difference in hand, locating the position on a map was a relatively simple matter of spherical trigonometry. (In modern practice, a navigational almanac and trigonometric sight-reduction tables permit navigators to measure the Sun, Moon, visible planets, or any of 57 navigational stars at any time that the horizon is visible).

The creation of a seaworthy timepiece was difficult. Until the 20th century, the best timekeepers were pendulum clocks, but the rolling of a ship at sea rendered the ordinary, gravity-based pendulum useless. John Harrison, a Yorkshire carpenter, invented a clock based on a pair of counter-oscillating weighted beams connected by springs whose motion was not influenced by gravity or the motion of a ship. His first two sea timekeepers used this system, but he became rightly convinced that they had a fundamental sensitivity to centrifugal force, which meant that they could never be accurate enough at sea. Construction of his third machine, designated H3, included novel circular balances and the invention of the bi-metallic strip and caged roller bearings (both inventions are still widely used today). H3's circular balances proved too inaccurate and he eventually abandoned the large machines. Harrison solved the precision problems with his H4 chronometer design. H4 appeared much like a large five-inch (12 cm) diameter pocket watch. In 1761 Harrison submitted H4 for the £20,000 longitude prize that had been offered by the British government in 1714. His design used a fast-beating balance controlled by a temperature compensated spiral spring. This general layout remained in use until microchips reduced the cost of a quartz clock to the point that electronic chronometers became commonplace.

After Harrison's work proved the possibility of portable precision timekeepers, making them practical by perfecting simpler and more affordable designs was the next problem. Pierre Le Roy and Ferdinand Berthoud in France, and Thomas Mudge in England successfully produced marine timekeepers. Although none of these makers discovered a path to simplicity, they did encourage others by proving that Harrison's design was not the only answer to the problem. The greatest strides toward practicality came at the hands of Thomas Earnshaw and John Arnold, who developed simplified, detached, "spring detent" escapements, moved the temperature compensation to the balance, and improved the design and manufacturing of balance springs. This combination of innovations served as the basis of marine chronometers until the electronic era.

The new technology was initially expensive, so not all ships were able to carry one of the devices, as illustrated by the fateful last journey of the East Indiaman Arniston. However by 1825, the Royal Navy had begun routinely supplying its vessels with chronometers.

It was common for ships at the time to use a time ball, such as the one at Greenwich, to check their chronometers before departing on a long voyage. Every day, ships would anchor briefly in the River Thames at Greenwich, waiting for the ball at the observatory to drop at precisely 1pm. This practice was responsible for the subsequent adoption of Greenwich Mean Time as an international standard. Time balls were eventually made redundant around 1920 by radio signals, which in turn are now being phased out in favour of GPS. In addition to setting their time before departing on a voyage, ship chronometers were also routinely checked for accuracy while at sea by carrying out lunar or solar observations.

Although industrial production methods began revolutionizing watchmaking in the middle of the 19th century, chronometer manufacture remained craft-based much longer. Around the turn of the 20th century, Swiss makers like Ulysse Nardin made great strides toward incorporating modern production methods, like fully interchangeable parts, but it was only with the onset of World War II that the Hamilton Watch Company in the US perfected the process of mass production, which enabled them to produce thousands of their superb Hamilton Model 21 chronometers for the US Navy and other Allied navies. Despite Hamilton's success, chronometers made in the old way never disappeared from the marketplace during the era of mechanical timekeepers. Mercer, in St. Albans, England, for instance, continued to produce high-quality chronometers by traditional production methods well into the 1970s.

Without their accuracy and the accuracy of the feats of navigation that marine chronometers enabled, it is quite likely the ascendancy of the Royal Navy and by extension, that of the British Empire would not have occurred, for the critical years forming the empire by wars and conquests of colonies abroad (One of many examples: The French were well established in India; there as elsewhere, where Britain was slow off the mark to colonize or trade, but were defeated by naval forces in the Seven Years' War, leading to India's later moniker "The Crown Jewel of the British Empire") occurred while the British fleets had the surety of navigation given by the chronometer, and their Portuguese, Dutch, and French opponents did not.

3345, Watches Australia.