Tuesday, August 7, 2012

Review - Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time by Dava Sobel

Short review: Sailors need to find out how to calculate longitude. England offers a prize. Clockmaker comes up with a solution.

Dangerous sailing
Until unknown clockmaker
Solves it with a watch

Full review: Sailors have been able to calculate latitude almost since men first set out onto the ocean. Calculating longitude, on the other hand, is a technology that has only been perfected in the relatively recent past. Many of the famous explorers whose names students now commit to memory set out with no reliable method of telling how far east or west they were, resulting in many deaths and extensive hardships for the crews involved.

Dava Sobel's book details the story of the Longitude Prize enacted by the British Parliament, the bizarre and impractical solutions offered to win the prize, and the lifelong efforts of John Harrison, a man who finally fulfilled the conditions necessary to win the Longitude Prize, but due to the prejudices and conflicts of interest of the commissioners charged with awarding the prize, was never actually awarded the bounty, despite having the backing of King George himself.

The method for determining longitude is fairly straightforward. One must calculate the local time where one is, and compare it to the time at some known position, which is now always assumed to be Greenwich in the United Kingdom. The difference in the local time and the Greenwich time can be expressed in hours, minutes, and second, and then plotted on a globe, showing the longitude of the ship in question. The prime difficulty facing the aspirants for the Longitude Prize was how to determine Greenwich time when one was presumably hundreds or thousands of miles away.

Astronomers, who favored methods using stellar and lunar observations, eventually settled upon a method that involved tracking the path of the moon across the sky, comparing its location to the locations of designated guide stars, and measuring the distance between the Earth and the moon. This method was complicated and difficult, and required massive numbers of celestial observations to be made before the required charts could be made to begin with. This method was also somewhat unreliable - on a cloudy night, one could not locate the stars needed, many days out of the month the moon is not visible (as it is located on the opposite side of the Earth), and so on.

John Harrison, on the other hand, sought to build a very accurate clock. Once such a clock was set to, for example, London time, one could simply refer to the clock at noon local time, and determine by seeing how far away from noon the clock was how many minutes and seconds of arc one was from London. However, the clock would have to remain accurate over long periods of time, in humid conditions, and across a wide span of temperatures. When the Longitude Act was passed, clocks were not even accurate to within several minutes per day, and even an error of a couple seconds per day would cause the navigator to miscalculate a ships position by dozens or even hundreds of miles.

The book describes Harrison's attempts to build such a clock, eventually settling upon an oversized watch. The book also describes the hostility many of the astronomers on the longitude board evaluating his submission had towards him. While Harrison was a tradesman, and a self-educated mechanic to boot (earning the derision of many of the highly educated aristocratic astronomers on the board), he was their competitor for the extremely lucrative prize. Under the guidance of successive Royal Astronomers, the board imposed more and more difficult obstacles to Harrison's watch, until in frustration he appealed directly to King George. Eventually, with the King's assistance, Harrison was awarded a prize by a special act of parliament. The obstinate longitude board never awarded the full Longitude Prize to anyone.

Sobel has created a compelling story out of what could have been a rather boring event in history. In a roundabout way, Harrison's story explains to a certain extent why pirates and privateers were common before the 1800s, and vanished almost completely thereafter. One thing made clear (to me at least) is that many writers of historical fiction, or even fantasy, make sea travel in the pre-Longitude era too reliable, and too easy. It is probably the measure of the success of a technological advance that it becomes so prevalent and accepted that the difficulties faced in the days before are forgotten by the general public. On that score, Harrison's watch is one of the most significant technological developments in history.

One nitpick I have is with the subtitle of the book. It seems to me that the longitude problem was not a scientific problem, but rather an engineering one. That failing aside, this is an excellent book.

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  1. Yes! I've been wanting to read this book - now I have to go buy it. Thanks, Aaron!

  2. @Julia Rachel Barrett: This was a very good book. I have another book by Dava Sobel I've been meaning to read. I'll have to dig it out and read it soon.

  3. It is a good read but I doubt it is a factual account

    The alleged "animosity" is a bit of an urban myth. How could the watch be considered totally accurate if the actual true longitude of the target port was unknown? Then the real time difference would be similarly unknown. How could you be totally sure that the watch did not gain time during the voyage and then, coincidentally, lose it so it appeared to be correct? This was the true basis of their doubts.

  4. @vincent: And you base your assessment on?

    The actual true longitude of the target ports was known. That's why they picked the particular target ports that were used. When you are testing something, you test it against known quantities to see if it will work.

    The animosity is well-documented, and Sobel demonstrated this throughout her book. Among other things, the longitude board would set standards, Harrison would meet them, and then the longitude board would move the goalposts.

    For now, I'll accept the research of a science author over your speculation. Do you have any kind of evidence to back up your arguments?