A Brief History of the Chronometer Essay Sample

A Brief History of the Chronometer Pages
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In Cartography, the Earth’s surface is divided into North-South divisions called latitude and into East-West divisions called longitude. Lines of latitude are parallel to each other with the zero line located at the earth’s equator. Lines of longitude on the other hand are geometric great circles which intersect each other at the North and South Pole. Any position on the Earth’s surface by specifying its degree of latitude and degree longitude.

In this age, finding one’s latitude and longitude is trivial to anyone with access to Google Earth. However such issues were not so trivial for sailors in the 17th century. Such issues were as important to 17th century sailors as it was hard. Not knowing where one was in the middle of the ocean could lead to unnecessary delays and even shipwrecks. The question of knowing one’s latitude was easily solved using celestial navigation. One’s latitude can be determined by simply looking at the elevation of the pole star. The latitude of your position is simply equal to the pole star’s elevation.

Longitude determination on the other hand was not as simple. Methods were either too inaccurate or too complex. Dead Reckoning involved deriving one’s position based on the previous location as well as speed and direction of travel. This was the easiest method but was highly unreliable. More reliable methods based on prepared tables and astronomical observations were available but needed a trained astronomer to prepare the needed observations. Such methods were also time consuming, often needing hours before one’s longitude is known (Tyson, 2000).

This problem of longitude was brought into public attention when in 1707, Sir Clowdisley Shovell and 2000 of his men got wrecked off of Sicily and lost their lives – all 2000 of them. The wreck was due to their failure to correctly identify the fleet’s longitude. (Royal Naval Museum)

As a testament to the necessity of determining an accurate measure of longitude. in 1714, the British parliament offered £20,000 for anyone who could produce a way to measure longitude to within 0.5 degrees. The device would be tested on an ocean voyage from Britain to the West Indies during which it should perform within the needed accuracy. As a testament to the perceived futility of the effort, the phrase “finding the longitude” became a catchphrase for idiotic and pointless pursuits. (National Maritime Museum)

A simple solution would be to use time. The sun travels across the earth in 24 hours, traversing 15 degrees of longitude in 1 hour. If we could know the time in a known location called the Prime meridian (like Greenwich, Britain) and your present location as well as the time in your location, we could deduce how many degrees our location was to the east or west of the Prime meridian. If for example, our current time is 1 hour ahead of the Prime Meridian, then we are currently 15° to the east of the Prime Meridian. As another example, if it is midnight where you are while it is high noon in London, then we could infer that we are on the opposite side of the globe – 180° from London. The longitude problem then boils down to the creation of accurate clocks.

Such clocks were already available however, these clocks relied on pendulums which lost its accuracy in the tumbling surface of the sea. It took a lowly, uneducated commoner named John Harrison to take on the academic and scientific community and win the Longitude prize by creating a clock that kept time in a ship – the Harrison Chronometer. His secret was relying on springs instead of pendulums so that his design was independent of gravity.

He constructed his first prototype, H1 from 1730 to 1735.  The H1 was tested on a voyage to Lisbon in order to test H1 during which it performed admirably. With this success, Harrison asked for money from the award body in order to build a second prototype. It took 25 years and two failed prototypes until the fourth prototype, H4 set sail for the West Indies aboard the ship Deptford.  The longitude prize’s specifications meant that the H4 could only be off by a maximum of two minutes when it arrived on its destination. After two months, the ship arrived on Jamaica where H4 was found to be off by only 5.1 seconds. Forty-eight years after its creation, the Longitude prize had been won but the Board of Longitude still wasn’t satisfied. A second test was conducted two years later on a voyage to the Barbados. Over the  6 week trip, the clock was off only by 39 seconds.

A copy of H4 was brought by Captain Cook on his second and third voyages of discovery. Captain Cook praised the timepiece feverishly upon his return calling it “our faithful guide through all the vicissitudes of climates”. Whereas people thought that only fools will be able to measure longitude, a 100 years later, only fools were thought to go to sea without a Chronometer onboard.

Bibliography

National Maritime Museum. (n.d.). John Harrison and the Longitude problem. In National Maritime Museum. Retrieved October 22, 2007, from http://www.nmm.ac.uk/server/show/conWebDoc.355/viewPage/2.

Royal Naval Museum. (2004). Biography: John Harrison. In Royal Naval Museum. Retrieved October 22, 2007, from http://www.royalnavalmuseum.org/info_sheets_john_harrison.htm.

Tyson, P.. (November 2000). Secrets of Ancient Navigation. In NOVA Online. Retrieved October 22, 2007, from http://www.pbs.org/wgbh/nova/longitude/secrets.html.

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