Chronometers

The invention of a marine clock (chronometer) which could be used to accurately measure longitude was arguably the most significant development in maritime navigation in the seventeenth and eighteenth centuries. Before their invention ships had great difficulty finding their way from one port to another. Fog, bad weather, and inaccurate charts made navigation, when no land was in sight, both dangerous and time consuming.

Latitude and longitude can be thought of in the same way as the index of a city street map with the latitude being north/south and the longitude being east/west co-ordinates. Once both are known a position can be accurately pinpointed. 

While latitude could be found by observing the position of stars longitude proved far more difficult to find. In fact an accurate means of finding an east/west position baffled navigators until 1759 when the clocks made by the Englishman John Harrison were finally acknowledged as being accurate enough to keep time at sea. 

In 1714 the English government had set up the 'Board of Longitude' to oversee the distribution of the enormous sum of 20,000 pounds to anyone who could devise a way of a measuring longitude. By the middle of the century two methods had emerged as the likely claimants for the money. The first of these, supported by the English astronomer Maskelyne, was based on observing the lunar distances of the moon to measure a vessels longitude at sea. 

The second was far simpler in theory but required an extremely accurate timekeeping device. This method, which would eventually win Harrison the prize, required setting a clock's time at a point of known longitude and keeping this time accurately during the corse of a voyage. This time could then be compared to the local time aboard the vessel and the longitude was then computed from this information. 

Harrison was awarded the prize money in 1773 after he completed five prototypes which were tested and found to be accurate enough to be used to find a ship's longitude. One of the conditions of the prize was that Harrison submit his prototypes to the examination of three other clockmakers selected by the Board of Longitude. As a result the Board of Longitude commissioned Larcum Kendall to make a copy of Harrison's fourth prototype, H.4, and it was this chronometer that was used by Captain James Cook on his second and third voyages to the South Pacific. 

From this period on navies and private shipping companies around the world began to purchase chronometers for their vessels. In England the best of them were submitted to the Board of Longitude and later the Royal Greenwich Observatory where they were tested and awarded prizes for their accuracy. The winners were then acquired by the Royal Navy, like Earnshaw's 520, part of the Powerhouse Museum Collection, which travelled with Matthew Flinders, were essential to the success of many historic voyages. 

The industry of which surrounded the making of chronometers lasted around 150 years before the use of radio time-signals in the 1920s essentially made them redundant. The chronometer became technically mature around the 1820s which was early in its development and this combined with their extreme durability meant many were in use for 50 to 60 years. In one example cited by Alun Davies a chronometer first used on board HMS Victory in 1796 was still being used in 1906. 

Aside from their extreme durability the failure of the British chronometer industry to modernise its methods of manufacture also played a part in the industry's decline. Most watchmaking companies, including Mudge, Earnshaw, Dent and Arnold, used hand crafted parts made in places like Prescott and Christchurch which were then finished in Clerkenwell. The maker whose name is on the instrument typically organised for the parts to be brought together and supervised the final stages of its construction such as 'springing' or adjusting the mechanism. By 1820 the British firms of Earnshaw and Dent as well as the French firm of Barraud used this system to produce chronometers in batches and dominated the industry. 

By the end of the nineteenth century a downturn in demand led to a decrease in the number of firms making chronometers. Of these the chronometer makers Mercer and Kullberg dominated the industry while a number of small independent makers modified basic models provided by these two large firms. In a move that sometimes makes attribution confusing these smaller firms often put their own names on the finished chronometer. To justify this they sometimes added a special feature of their own before putting their name on an instrument supplied by a larger firm. That this was no small part of the industry can be seen in the example of Mercer who in the 1890s supplied chronometers to over 150 nautical opticians. 

A final flurry of activity followed during the First World War but at the finish of the conflict the Admiralty found itself overstocked with chronometers. Outstanding orders were cancelled along with the Greenwich chronometer trials. Some makers like Mercer diversified into other branches of engineering but many simply disappeared. The introduction of the radio-transmission of time-signals in 1924 effectively sounded the death knell of the mechanical chronometer in Britain. Even so they are still recognised for the quality with which they were constructed and the important place they hold in development of Colonial enterprises across the globe. 

References
Davies, Alun, 'The Rise and decline of Chronometer Manufacturing', Antiquarian Horology, Number 3, Volume 12, 1980
Gould, Rupert, T., 'John Harrison and His Timekeepers', monograph reprinted from The Mariner's Mirror, Quarterly Journal of the Society for Nautical Research, Great Britain, 1935 
Howse, Derek, Greenwich Time and the Discovery of the Longitude, Oxford University Press, Melbourne, 1980
May, W. E., A History of Marine Navigation, G. T. Foulis & Company Limited, Oxfordshire, 1973
Tooth, Thomas, It was All a Matter of Time, Thomas Tooth, Katoomba, New South Wales, 1993