The name John Harrison clockmaker will ring a bell with lots of people interested in antique clocks. Harrison was one of those special people that only ever come round ever generation or so. He was self educated and he started out on his journey as a humble carpenter but it was his love for clocks that made his so well known. John Harrison dedicated his lifes work to solving the longitude problem. It was fairly easy to find out ones latitude while at sea but finding your Longitude was not easy in the 18th century. The problem of finding ones Longitude at sea was of vital importance and our British Parliament offered a prize comparable to nearly 3 million pounds in todays money to find a solution in 1714. Many sailors have lost their lives by miscalculating their position by not knowing their exact longitude. It was Harrison who eventually collected this prize. His clocks are able to be viewed at Greenwich National Maritime Museum. The advent of the marine chronometer as we know today could not really have been carried out without the input and development of various other influential horologist of their time though.
One of the first attempts to invent a marine chronometer was made by the inventor of the pendulum clock, Christian Huygens, in 1675 he invented a chronometer but after tests it was not found to be accurate enough. Pierre Le Roy’s invention in 1748 of the detent escapement which is an important part of all later chronometers was also vital in the development of the chronometer, he incoorporated this detent escapement with a temperature compensated balance and the isochronous (equal time intervals) balance spring. Thomas Earnshaw and John Arnold in 1780 also were influencial in this field. They developed and patented simplified and detached spring detent escapements. They improved the escapements by bringing the temperature compensation to the balance, and improved the design and manufacture of the balance springs.
It is in my view the work started by John Harrison combined with the people listed above and various other individuals like Ferdinand Berthoud in France and Thomas Mudge in Britain that served as the basis for marine chronometers as we know them today. Marine chronometers pictured like the one above by Charles Frodsham can be seen still being used up until the World Wars, many years later. It is not until the electronic era and satellite navigation did these chronometers become retired to their various collectors homes and museums.
There were various difficulties for keeping precise time at sea, these chronometers solved these in various ways. The rolling motion of the boat was not good for these antique clocks and so the clocks movement were housed in a case and this case was attached to a gimbals that kept the movement horizontal under even the worst storm. These can be seen in the picture above and below.
The salt air was also not good for the mechanisms and the chronometers were sealed to be airtight.
Also temperature variations was one of the most important factors to overcome, temperature compensated balances reduced these erros to a minimum.
Spring driven fusee movements also compensated for the changes in the spring tension during the wind of the chronometer.
On a final point the addition of a winding cover to the rear of the brass cover for the movement was also added. On one fateful journey a spider entered the movement of one chronometer and slowed the mechanism. This caused the captain to wrongly position his boat on the charts. The boat hit rocks and many sailors lives were lost. Ever since then a cover was added to prevent this reoccuring. The picture below shows one way this was achieved. On later models a spring loaded disc was used. This needed to be held back while winding.
The marine chromometer was vitally important in the 18th and 19th centuries and was one of the reasons why this country remained one of the foremost naval powers. Its importance should not be understated. We always tend to have good examples at www.pendulumofmayfair.co.uk for sale.