For the safety of navigation it is essential to know the position at sea, particularly the longitude . From early historical times til the eighteenth century the method of lunar eclipses was used, as these could be predicted and are observed simultaneously at all points on the Earth when the Moon is above the horizon. However the phenomenon, because of its rarity, was of little use to the crew, also because the determination of contacts was not sufficiently accurate.
Another celestial phenomenon, which allowed to determine the exact time of observation from which to deduce the longitude, was discovered and proposed by Galileo, in 1610, as being superior to the old method of lunar eclipses: it was the observation of the eclipses of Jupiter's satellites, so frequent that it can be observed several times every night.
Still another phenomenon that was proposed by Renaissance astronomers was based on lunar distances. In summary we can say that the Moon moves like the hand of a clock that turns on the "dial" of the sky, so that its position may be indicated at any time by the angle, rapidly changing, that it forms with another star. This angle is the "lunar distance" and, its value, previously calculated for the meridian of reference in the ephemerides, allowed to obtain the time at the meridian of the observer (Capasso 1994).
Already in the fifteenth century ephemerides were compiled by astronomers who observed and studied the motions of the moon to find the laws that made it possible to predict and record, with their coordinates and the subsequent hours of sunshine, the positions of the star on the celestial sphere.
The problem was of great importance to maritime nations, and in the second half of the seventeenth century arose important astronomical observatories, whose aim was the study of the motions of the stars for the determination of longitude: the one in Paris became operational in 1671 and started in 1679 the publication of the Connaissance des temps (later taken by the Bureau des longitudes), that gave the first angular distances of the Moon from the Sun and the major planets; the one in Greenwich , founded in 1675 by Charles II, supported and directed by John Flamsteed , started after a century the publication of the Nautical Almanac, an initiative of the royal astronomer Nevil Maskelyne, and immediately adopted by all maritime nations.
All these methods were still insufficient to solve the fundamental problem, whose solution needed to operate a clock with the time of the meridian of reference indicating exact values by any navigation condition. A timepiece with a perfect regularity, despite the movements of the ship, was required, that, once set at the hour of the meridian, was able to preserve the timing within seconds: a delay of 4 seconds produced an error of 1 minute in longitude.
The first idea to equip vessels with a precision clock dates back to the sixteenth century; it is questionable wether the priority should be attributed to Fernando Columbus, brother of Christopher or to Gemma Frisius (1508-1555), professor at the University of Louvain, of whom was a pupil Mercator . The first one proposed the method in 1524 to the Commission in charge of establishing the line of demarcation between the possessions of the Spanish and the Portuguese, under the Treaty of Tordesillas. Frisius wrote about the benefits of it in De Principi Astronomiae et Cosmographiae (Antwerp 1530), suggesting the use of small mechanical clocks, available at the time.
According to tradition, these clocks were first used by the Dutch navigator Willem Barentsz (1550-1597), in his expedition to the polar regions. In the records of the polar expedition by C.R. Markham, an illustration represents the Barentsz hut, as described by Norwegian Captain Elling Carlsen, who found it in 1871, with a clock hanging on the wall, likely a spring clock.
The first mechanical watches, weight driven, date back to the Middle Ages and were followed by spring clocks, which were developed during the second half of the seventeenth century with the application of the pendulum according to the ideas of Galileo. In 1659 Christian Huyghens (1629-1695) built pendulum clocks suspended to a gimbal, designed to keep them vertical while navigating. The experiments proved unsatisfactory and the project was abandoned.
In 1714, at the initiative of mathematician W. Whiston, in England was formed a Board - the Board of Longitude - which, with the appropriate Longitude Act, raised a prize, with earnings varying from 10,000 to 20,000 pounds depending on the accuracy achieved, for those who could make a marine chronometer able to determine the longitude with an approximation between 1° and 0.5°.
The "challenge" was accepted by John Harrison (1693-1776), a native of Yorkshire, the son of a carpenter, who, lured by the prize, built his first marine chronometer in 1715, consisting mainly of wooden parts.
In 1735 he presented the so-called number one, a clock driven not by a massive pendulum, but by two rocker arms connected by wires so that their movements were opposed to each other, counteracting the effects of ship movements. Among other innovations, it had a new type of escapement, two springs, a device that allows its operation even while charging, and a temperature compensating device.
The instrument was tested during a voyage from London to Lisbon on the ship "Centurion", but although the result was positive, the small difference in longitude between the two locations did not permit to certify the performance. So Harrison got only a modest advance on the promised prize , as an encouragement for developing a second model, which also received a second partial prize. It took him more than seventeen years to submit the third watch which, however, like the second one, was only a little smaller than the number one, that weighed about 31 kg.
It is therefore surprising that his fourth clock, the famous number four, was a nice flat chronometer with a diameter of only 12 cm, not much different from pocket watches used until a few decades ago.
It was tested first, with great success, on the ship Deptford on their way to the West Indies, and a second time on the Tartar, but the prize was not fully paid (and was awarded only in 1773 at the end of his life), as the Board required a review of the mechanism by a group of experts, one of them being the watchmaker Larcum Kendall (1721-1795).
Kendall in turn made a stopwatch on the model of Harrison's number four, introducing improvements; it was tested in 1772 on the "Resolution" by James Cook , who was enthusiast and used it again in the third voyage. It was also used by J. Vancouver in 1791, during his memorable voyage of circumnavigation in search, along the American coast, of the north-western passage to Northeast.
At the request of the Board, Kendall designed and produced in 1772 and again in 1774, two timepieces, with further modifications to the prototype of Harrison. The Kendall No. 2 had a history of adventure and romance: it was handed over to capt.Phipps for his polar expedition of 1773 and in 1787 was assigned to capt. Bligh.
It was then in the hands of the mutineers of the "Bounty", so it remained at Pitcairn until 1808, when it was purchased by the commander of an american whaling. Stolen to him, years later reappeared in Concepcion in Chile, where it was bought by a Spanish adventurer. At his death in 1840, was eventually sold to a British officer who brought it back to his country: after more than sixty years, the clock was still running, despite its vicissitudes.
As the clocks of Harrison and Kendall were of cumbersome construction and not akin to further improvements, the British government offered a reward to those who could make an improved instrument.
The challenge was taken by Thomas Mudge (1715-1794), another famous clockmaker, who, in 1765, had been a member of the commission to evaluate the timepiece of Harrison. In 1774 he presented his first model, that had a timespan of eight days between charges, and two other models, tested in the eighties, and known as "the Blue" and "the Green", the color of the case. These did not however receive the approval by Maskelyne.
A substantial improvement of those first timers is to be attributed to the french Pierre Le Roy (1717-1785) and to Ferdinand Berthaud (1729-1807), born in the canton of Neuchatel, that after became a major production center in Switzerland.
The first one presented his watch at the Academie des Sciences in 1766 and tested it successfully on the frigate Enjouée in 1768, on a voyage from Le Havre to Newfoundland and back. His major contributions ly in an innovative type of escapement, defined as "à détente", or "on release" and in the compensated rocker arm.
Berthaud moved to Paris in 1745 and in 1762 began to devote himself to watchmaking; he was by far the most prolific author of treatises on clocks and a versatile manufacturer of many types of timepieces.
But the time required for making a timepiece ranged from three to two years and the costs were prohibitive, because the watchmaker was a lone and secretive inventor. Therefore these first timepieces were valuable tools for the exclusive use of government authorities and were only loaned to the great explorers-hydrographers during their journeys.
The mass production for general use, and then the solution to the hystorical problem for sailors, is due to the British John Arnold (1736-1799) and Thomas Earnshaw (1749-1829).
Arnold improved the innovations introduced by Le Roy, and had the intuition, unlike his predecessors, to establish a company in which make use of skilled workers (that, in turn, became watchmakers) for making parts, reserving to himself the mechanics of the instrument. In this way he, at the end of the eighteenth century, had produced a thousand timepieces at low cost, many of which were employed on board. At his death the company was continued by his son John Roger and, at his death in 1843, was taken over by Charles Frodsham.
Earnshaw is credited for having further improved the escapement and the rocker arm, making them roughly as we know them today.
A few decades ago, the mechanical clock has been replaced by quartz, which maintains the traditional appearance, in its elegant mahogany box, while the movement has little in common with the clock of the past: the controlling element of time is represented by a quartz crystal placed in an oscillating circuit, whose high frequency stability ensures a very stable time base, regulating the movement of hands with an accuracy of few tenths of a second per day. The power supply is a battery and the charging interval is at least one year.
Another advantage is that the quartz clocks are insensitive to movement of the ship and to any type of noise. Moreover, when made as a control system, the timepiece can pulse a high number of clock repeaters located in different rooms on board, to ensure the correct timing to all guests of the ship.