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Longitude (Book Review)

Longitude by Dava Sobel

The sailor in my bones called out to read Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of his Time by Dava Sobel. The longitude problem had plagued seafaring civilisations since Ptolemy. It was a scientific problem that eluded answers until, in 1773, an Englishman named John Harrison, after forty years of experimentation, development and political warfare, claimed the 20,000 pound reward put forward by the Longitude Act 1714. This was the pressing scientific question of the age.

Consider the scientific simplicity of the latitude problem that can be understood through cosmic cycles including the length of a day or the height of the sun or by identifying known stars above the horizon. Latitude is a series of concentric circles that include the Equator where the Sun passes closest to the Earth and the tropics of Capricorn and Cancer that respectively mark the sun’s extremes of journey from Southern-most-to-Northern-most traverse. Latitudes are a series of parallel lines around the planet. Any sailor could know their latitude, how high up or low down a parallel line they were traversing, because latitude is fixed by the laws of nature. But consider the complexity of determining longitude.

Longitudinal lines aren’t concentric along the paths of the Sun’s rotation around the Earth. They certainly aren’t parallel. The meridians of longitude run from North Pole to South Pole in slices that thicken as they approach the Equator. If the planet takes 24 hours to travel 360 degrees and an hour marks 1/24th of the journey, one hour marks 15 degrees of that rotation. This means that the solution to finding longitude is about the difference in time between two locations. Longitude becomes even more difficult at sea where a lack of geographic and civilization-based reference points aren’t exactly etched into the local environment.

To solve the longitude problem you need to know the time in the port of departure and the current time at the current position along a journey. An hour’s discrepancy is 15 degrees longitude. At the same time, 15 degrees at the equator equals 1,000 miles and 15 degrees at either Pole is approximately nothing. So, when it comes to time, four minutes wherever someone travels will equate to a degree of time, but a degree of distance can encompass a broad range in miles traveled.

Imagine the problem of Admiral Sir Clowdisley in command of five ships in 1707. Returning from victory, he understood the fleet’s latitude. But he had no three-dimensional idea of longitude, their position could have been hundreds of miles north or south. And, for a sailor, this could mean the haven of the intended port or a cold death on the unexpected rocks. This is exactly why longitude was so important – trade or war depended on that three-dimensional accuracy of knowing a ship’s location with certainty. Clowdisley lost 2,000 troops, four of his five ships, and barely survived the day. Why? Because the prevailing solution to longitude had been the art of dead reckoning.

And that is where John Harrison, an untrained clockmaker, made his mark on the history of longitude. First, he battled those that would have tried to find an answer in astronomy. And, second, he developed a series of clocks that incrementally solved the problems that clocks had in providing the longitude solution. Imagine the pendulum clocks of the day. They were subject to the pitch and yaw of the ship. That meant time slowed and sped up depending on the waves. And the Longitude Act 1714 called for a specifically small margin of error in time between ports over a number of months to be called successful. Clocks were also subject to temperature. The longitude solution had to be solved for ships on the hot Equator as they would be in the icy Arctic Circle surrounded by ice. Temperature and pitch affected the clocks of the day. And this preoccupied Harrison (and his competitors) for 40 years.

Harrison’s solutions put forward for the prize money ranged from the lumbering H1 through to a wrist-worn H4 that became a working solution for longitude. Each one incrementally solved pressing problems. And a clock based solution made enemies along the way like the Reverend Nevil Maskelyne, fifth astonomer royal. Some though the answer was, like everything, to be found in the stars. So, even when Harrison should have taken the prize, his clocks were often passed over or suffered political sabotage in the testing.

This is a book of science, adventure, competition and a certain degree of historic trivia. A most compelling read.

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Steven Clark Steven Clark - the stand up guy on this site

My name is Steven Clark (aka nortypig) and I live in Southern Tasmania. I have an MBA (Specialisation) and a Bachelor of Computing from the University of Tasmania. I'm a photographer making pictures with film. A web developer for money. A business consultant for fun. A journalist on paper. Dreams of owning the World. Idea champion. Paradox. Life partner to Megan.

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