TNB Night Owl – The Longitude Quandary, Part Two

Harrison H4 Clockwork. Photo by Mike Peel.

[Part one explained the eighteenth century navigational problem of determining longitude. Part two discusses the solutions that were found.]

With the Longitude Act of 1714, the British Parliament established a monetary award for whomever could devise a method to determine longitude with an accuracy within defined specifications and tests. A Board of Longitude was also created to judge the worthiness of claims for the reward and, if found successful, to reward the claimant financially.

The tests required a sea trial from Britian to the West Indies in which the device or method being evaluated was employed to track longitude. Upon arrival at the destination port, the longitudinal location determined by the device or method was compared to a landmark, the longitude of which was already well known. To earn a reward, results had to be accurate within a certain distance or degree of longitude, as follows:

  • Within 1 degree, a reward of £10,000
  • Within 40 minutes (two-thirds of one degree), a reward of £15,000
  • Within 30 minutes (half of one degree), a reward of £20,000.

(Note that at the equator, one degree of longitude is equivelant to 60 nautical miles, or 69 miles, or 111 kilometers – closer to the poles, one degree of longitude decreases in distance until it reaches zero miles or kilometers at the poles).

This was an enormous amount of money at that time. Most of the international effort to find a solution went into trying to build a better clock. Only one clock maker succeeded, with little in the way of competition from other timepieces or other methods.

Englishman John Harrison (1693-1776) was a carpenter by trade, who had developed an interest in time keeping and clock making. Self-educated, his first clocks were made entirely out of wood. Motivated by the Longitude Act (either by the challenge or the money) he continued to improve his clocks.

By the 1730s he’d designed what became known as H1, the first marine chronometer, which still used some wood parts. The Board of Longitude was interested enough to authorize a sea trial in 1736 to Lisbon, but not to the West Indies. The H1 wasn’t perfect but it succeeded in earning Harrison £500. The Board wanted to see improvements, so awarded half in advance and the other half after promised improvements were completed.

Harrison went on to design and build H2 and H3, both of which he eventually realized had design flaws. In the 1750s, after two decades of work on H2 and H3, he began work on H4.

H4 was a dramatically different design than any of Harrison’s previous chronometers. Not only was it much smaller, the internal operating mechanism was entirely different. H4 resembled a large pocket watch, but it ticked five times per second, instead of the usual one tick per second – and it was far more accurate than anything he’d built thus far.

By the time H4 was ready to be tested, two other methods for determining longitude had gained the attention of the Board of Longitude. German astronomer Tobias Mayer had made highly accurate observations of the moon and compiled lunar tables that theoretically made it possible to determine longitude at sea to within approximately one-half degree. Christopher Irwin had invented a chair that was supposed to make observation of Jupiter’s moons possible from a ship, even in rough seas. This method of determining longitude was already tried and true on solid ground, but had never succeeded at sea.

The Board of Longitude in 1763 commissioned Nevil Maskelyne (1732-1811), who later would become the fifth Astronomer Royal (1765-1811) to sail to Bridgetown, the capital city of Barbados, in the West Indies. Maskelyne’s assignment was to test the three competing methods. He reported back to the Board that Harrison’s chronometer was accurate to within 10 nautical miles, while Mayer’s lunar distance method was accurate to within 30 nautical miles. Irwin’s chair did not succeed in passing the trials.

The Board eventually rewarded both Harrison and Mayer, noting that Harrison’s timekeeping method and Mayer’s lunar distance method complemented one another and would be useful together onboard ship. Harrison had to fight the Board to get all the money he believed he deserved. In all, he received a total of £23,065 – the last of it only three years before his death (at age 83). There was quite a bit of drama involved that I won’t go into, but it did leave me wondering if the Board of Longitude, who represented the wealthy upperclass of Britain, had treated Harrison, a mere carpenter and thus a member of the working class, unfairly.

Harrison spent nearly his entire adult life, from about 21 until 80 years old, either building and perfecting his chronometers or fighting for his financial reward. That’s an impressive record of perseverance.

While Harrison’s chronometers are obsolete, accurate timekeeping is still crucial in navigation today. GPS satellites have onboard atomic clocks which are critical to the precision of the GPS system. Navigation throughout the world, by land, sea, or air, has never been safer. For the last 250 years, travelers, commerce, and economies, have all benefited from the solutions found to the longitude quandary.

Question of the night: If you could save time in a bottle (hat tip to Jim Croce), what would you do with it?

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About Richard Doud 622 Articles
Learning is a life-long endeavor. Never stop learning. No one is right all the time. No one is wrong all the time. No exceptions to these rules.