A
Story of Time
© Isle of Man Government
| . | . | . |
|
A
Story of Time |
|
| British Development of Precision Watch |
| . |
| With the aid of the global positioning system, a navigator can, today, fix his position on the surface of the earth instantly and accurately to within a few metres. In the 17th Century, a period of important navigational exploration, only latitude, the position north or south could be found accurately. Longitude, the position east or west, would be approximated aboard ship by consideration of the number of days of the voyage and the estimated speed and course of the ship. This could lead to huge errors and frequent loss of ships. Many ships simply vanished after months of voyaging without ever sighting their goal. The crews, pitifully reduced in numbers, could no longer sail the vessel. Others, believing they were in safe waters, would discover their error only after wrecking on unsuspected rocks. The most notable of such mishaps occurred in 1707 when Admiral Sir Cloudesley Shovel, believing his fleet to be in safe waters, maintained his course. But that night in fog, they ran on the Scillies losing four ships, nearly two thousand men and the Admiral himself. With increasing losses caused by expanding trade, essential to the wealth of the nation, an Act of Queen Anne in 1714 offered the magnificent award of £20,000 for a means of determining the longitude at sea. The award attracted enormous interest among academics, astronomers and clockmakers. The two most promising means of success lay in astronomy and timekeeping. The Astronomer Royal believed that the longitude could be found by observation of the moon's motion against the background of the stars, called the "lunar distance method". If the motion is known with sufficient accuracy, tables can be drawn up forecasting the position of the moon for a large number of times at Greenwich. The difference between the local time at sea and Greenwich Time (determined by lunar observations and the tables), would be the ship's longitude. But this method ignores the difficulty of making accurate observations from the deck of a heaving ship as it also ignores the complex and lengthy mathematics required to complete the exercise. The smallest mistake arising from either task could put the ship in greater danger than the system of dead-reckoning already practised by navigators. The second method needed a precise timekeeper that could maintain its rate under all conditions of use including storm seas, extremes of temperature, the ageing of primitive oils and violent movements of the ship. Given that such a timekeeper could be developed, it would be set to Greenwich Time at the start of the voyage. At any time during the voyage, the difference between local time by observation of the sun, and the Greenwich set chronometer will be the difference in longitude. Thus: there being four minutes of time to each degree of circumference of the earth, if the difference is 60 minutes after Greenwich Time, then the ship is 15 degrees east of Greenwich. Such a portable timekeeper had never been envisaged, it being impossible in the early 18th century to compensate for temperature changes and there was only the primitive verge escapement to control the rate. But the man who was to solve the problems and reap the reward was at hand. JOHN HARRISON 1693-1776 22p - 29p
The self-educated son of a Yorkshire carpenter, John Harrison built his first clocks in about 1713. By the mid 1720s, he was making clocks which were to set the standards for his individuality of thought and design. Made of oak, and of primitive appearance, the movements employed ligmun vite bearings and anti-friction rollers to avoid necessity for oil, his own invented escapement, also without oil and with temperature compensation utilising the effects of the differing coefficients of expansion of brass and steel rods. With these methods, he demonstrated his declared contempt for conventional methods of clockmaking. With his sights fixed upon the longitude prize, he began the construction of his first longitude timekeeper to include his temperature compensation and oil-less escapement. This machine, now designated "H1" weighs some 70 pounds and took six years to construct. It was tested at sea in a voyage to Lisbon and with it, Harrison showed that the ship's navigator was in error by some 90 miles at the conclusion of the test. Dissatisfied with the machine but encouraged by the results, he applied to the Board of Longitude for funds to make another, improved version. Two more machines were constructed during the following 19 years without achieving the success he wanted, although to encourage the Board of Longitude to continue to advance money for the work, members of the Royal Society testified to the usefulness of his mechanisms. It was in 1755 that Harrison, disappointed with numbers 2 and 3, which were like No 1, big, heavy machines, changed his whole philosophy of design and produced a machine in the form of a watch some 5 inches in diameter. Completed in 1759, this watch employed a form of verge escapement with diamond pallets energised by a small, separate mainspring wound at 7 1/2 second intervals. This secondary power spring ensured a constant force at the escapement to prevent power fluctuations giving rise to variations in timekeeping. In two voyages to the West Indies, the timekeeper performed with outstanding accuracy and well within the parameters set by the Longitude Act. Harrison had fulfilled every condition of the Act and was entitled to the £20,000 reward. But it was to be a further 11 years of bitter wrangling with the Board supported by the Astronomer Royal, before he finally received the full amount and this, final capitulation, because King George III intervened on Harrison's behalf after testing a fifth timekeeper in his private observatory. THOMAS MUDGE 1715-1794 34p
In 1774, as a contender for one of the subsidiary longitude awards, Mudge developed his own complex timekeeper. He worked towards perfecting this for the remainder of his life but it proved to be too complex for general manufacture and, as with Harrison's timekeeper, only the maker could persuade it to keep close time. Once again, the Astronomer Royal was responsible for supervising the tests and showed himself to be a rigid and unsparing critic. But Mudge was to make a much greater contribution to the precision timekeeper with the invention of his lever escapement. He had been apprenticed to the celebrated George Graham, FRS, inventor of the Graham escapement for pendulum clocks. By dispensing with the pendulum and applying instead a simple balance and spring, he invented in 1754 the escapement that was eventually to dominate the watch industry. Apparently unaware of its importance, he dismissed it from his mind in order to continue work on his timekeeper and left it to others to demonstrate its effectiveness as the best escapement for watches. During the 19th century, it came gradually into common use. For both short and long term use, it was most beneficial to industry and science and set new standards of general and domestic timekeeping. When the railways adopted standard timetables, the lever watch was especially useful and the complimentary description "railway time" was applied to the guard's watches. The escapement dominated the watch for civil use and, only now, at the close of the 20th century, some 250 years after its invention, it is to be superseded. JOHN ARNOLD 1736-1799 38p
Arnold produced his first timekeeper in 1770 and was confident enough to submit it to testing by sea voyage. They went badly and he was criticised by the Board of Longitude who refused to advance more money for future experiments. Put on his mettle by this setback he set to and devised new forms of temperature compensation, new balances and balance springs and new escapements. He was the most prolific of the experimental innovators with no less than three escapements and four balances with temperature compensation. Once he had settled upon a satisfactory mechanism, he was able to train his workmen to produce his watches to uniform designs at quite modest prices. As a consequence seamen could afford to buy their own watches for navigation. Ship owners were reluctant to equip their ships with chronometers, so that Arnold's production at affordable prices made a unique contribution to international trading and the expanding wealth of the nation. THOMAS EARNSHAW 1749-1829 44p
The last of the pioneer constructors of precision timekeepers, Earnshaw invented his chronometer in 1780. In the principles of its action, it is similar to Arnold's escapement in that the balance is detached from the escapement after the energising impulse. Much of the development work for timekeeper escapements had been done when Earnshaw arrived on the field but his escapement is original and simpler to make than Arnold's. Earnshaw's major contribution was the development of the components to give rigidity and therefore, stability to the escapement. His interpretation of the design of the escapement lasted until the end of the industry in the 1980s and, up to that time and from the mid 19th century, both Merchant and Royal Navy ships carried chronometers designed on Earnshaw's principles. Dr. GEORGE DANIELS MBE, DSC, FSA, 1926 - 26p
The single problem with Mudge's lever escapement is the
necessity for lubrication at the engaging surfaces of the components. As a consequence it
must be serviced at short and regular intervals if it is to keep close time. Seeing that a
new escapement without a lubrication problem would be beneficial to the mechanical watch
industry, Daniels invented the Coaxial escapement. By radical redesign of the engaging
components, the sliding friction of the lever escapement has been avoided. As a result,
the timekeeping is no longer influenced by the condition of the lubricant and remains
stable for long periods without need of servicing. It is the first, practical new watch escapement for 250 years since the invention of the lever escapement by Thomas Mudge in the 18th century. Its performance under all conditions of use has been shown to be superior in both long and short term trials. But changes take place slowly in the industry which is reluctant to adopt new ideas. As a consequence, it has taken Daniels 25 years to persuade the factories to change from the lever to the coaxial escapement. Now with its adoption in the Swiss industry, it marks the final, significant British contribution in the 20th century to the development of the portable, mechanical, precision timekeeper independent of electricity and is planned to sustain public affection for the mechanical watch through the 21st century. Our Theme & Technical Designer for this issue is Dr. Daniels MBE, DSC, FSA, who has made a significant British Contribution in the 20th Century to the development of the mechanical watch. He has been resident in the Isle of Man for many years, his enthusiasm for the subject is infectious which is clearly illustrated by this fascinating stamp issue.
Acknowledgements: The Isle of Man Post Office would like to
acknowledge the very kind assistance given by:
Isle of Man Post Office Tel: +44 (0)1624 698430 You can order the shown stamps at following
web-adress/
|
|
zu Top