The Kew Observatory, not far from London, played an important role in timing trials attracting watchmakers from around the world during the latter half of the 19th century. The competitive rating of chronometers by observatories in Geneva and Neuchâtel in Switzerland, Besançon in France and Kew in England lasted from 1873 to the late 1960s. The observatories delivered rating certificates and awarded distinctions to the best-performing chronometers. Representing the last word in accuracy, the prizes opened the doors to the major customers for 19th century watchmaking—governments and navies. Since Britain was the major naval power, the Kew certificate became the most prestigious in the eyes of the world’s watchmakers.
The exact time was indeed a valuable commodity and a major issue for the maritime powers from the middle of the 18th century. The marine chronometer provided the easiest way of finding longitude at sea and hence the ship’s position. The country that found a way of keeping the exact time at sea would rule the waves. Britain was the first to solve the longitude problem in 1753 and became the leading sea power.
In those days the exact time was always determined by observatories and calculated on the transit of heavenly bodies. The Earth’s path around the sun gave the year, the lunations, the months, and the period between the sun’s transits gave the day, subdivided into hours and minutes. The observatories were therefore the guardians of time providing the reference against which all clocks were set. They were the source of time and the providers of exactitude.
But that wasn’t any use to ships at sea which had to rely on a portable time reference. This was to be the role of the marine chronometer. Its development was spurred by major disasters at sea, which launched the quest for horological exactitude. On July 8, 1714, the British parliament passed the Longitude Act, promising 20,000 pounds sterling for a way of fixing the position of a ship at sea to within half a degree of longitude.
It was a huge prize, equivalent to some 20 million euros today. John Harrison found the solution in 1759 by comparing the time at the port of departure with the local time at sea determined by sextant. Harrison tested his H-4 marine chronometer on a journey to Jamaica and back. On returning, it was calculated that the watch had lost only five seconds on the 81-day outward voyage. Harrison eventually won the Longitude Act jackpot and Britain’s mastery of the seas.
The Royal Observatory of Greenwich near London organized the first timing contest in 1766, but the competitions were sporadic. The first annual chronometer competitions were staged by the Geneva observatory from 1816. The criteria and test procedures developed in 1879 by the observatory’s director Emile Plantamour, were so stringent that were adopted by Kew in 1884 and Besançon in 1885, along with a points system codified in its regulations.
Baume entered the Kew rating contest for the first time in 1885, and won several prizes. In 1892, Baume triumphed with a chronometer that won the highest score until then awarded at Kew—91.9 out of a possible 100. For 10 years it held the record as the most exact timekeeper.
The significance of these marks becomes clear with an appreciation of the way these chronometers were tested. The regularity of the rate of a watch is above all determined by the position and the ambient temperature in which it is tested. The force of gravity affects the rate of the balance according to its horizontal or different vertical positions, while in changing temperatures, the expansion and contraction of metal parts, notably the balance-spring, similarly causes a change in rate.
In the trials, chronometers were rated for 40 days in different positions and temperatures (refrigerator, room and oven) for periods of several days. In each period, the mean rate variation against the observatory’s reference clocks was calculated.
To establish a score for the chronometer, the aggregate rate variations were usually reduced to a base of 100. The fact that the laboratories marked out of 300 or 1,000 made it difficult to compare scores. The maximum score (100 at Kew) was theoretical. The higher the marks, the closer the rate of the chronometer to that of the observatory master clock.
The testing procedure changed somewhat over the years, but according to the Geneva Observatory rules, on which were based those of Kew and other observatories, rate variations were measured in the following test conditions: pendant up, 5 days; pendant right, 5 days; pendant left, 5 days; dial up in refrigerator, 6 days; dial up, 6 days; dial up in oven, 6 days; dial down, 6 days; pendant up, 5 days. The test thus lasted 44 days.
With the advent of quartz watches in the late 1960s, which were many times more exact than the best mechanical chronometers, the timing trials lost their relevance. Rating at Kew was transferred to the National Physical Laboratory at nearby Teddington in 1912, and the NPL stopped testing mechanical watches in 1978.
Today the reference time is provided by atomic clocks the rate deviation of which is around one second in three million years. In Switzerland, rating certificates are delivered by COSC the official chronometer inspection body, even though its requirements are not as strict as in the former timing trials.
Courtesy:Baume & Mercier
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