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March 10, 2006

Longitude - Dava Sobel

On the cover of this book, it says boldly "The true story of a lone genius who solved the greatest scientific problem of his time". Having now finished reading, I think this hyperbole over-eggs the pudding somewhat in an attempt to lure readers in. Of course, it worked! This short popular science book has sold an amazing number of copies since it's first release in 1996. It's great success is down to the fact that it is short, and sticks pretty much to the point. People could see themselves finishing it, understanding the problem, and even the solution. Those readers who completely lost the plot with Stephen Hawkins' "Brief History of Time" (and that probably included just about everyone), could feel good about themselves a bit more. We have Sobel and her success to thank for allowing many other great popular science books to find publishers too I think.

But, unfortunately, it's not really a great science book.

The problem itself isn't quite as esoteric or interesting as you might think. John Harrison was a clockmaker, and he knew what he needed to do right from the start. It wasn't really a struggle to find the answer to a difficult intellectual problem. All he needed to do was build a clock that would be accurate even when positioned on a ship sailing across the Atlantic ocean. It was just a mechanical trial and error procedure, performed over years of painstaking work I admit, but not really that interesting from the outside. And he wasn't really alone, his son helped him a lot in his efforts. I'm not saying he wasn't a genius clockmaker, he did invent new methods for controlling mechanisms to measure time, but in this book the science of those discoveries is hardly covered at all.

The Longitude problem, briefly stated is this: when a ship is at sea, it is simple to measure the latitude from the positions of the stars and the sun. However, no good method existed in the 17th century for measuring the longitude. So a ship sailing across an ocean had very little idea how far towards the east or the west it had travelled. This could be disasterous and was the cause of many shipwrecks. The simple answer is to have an accurate clock on board your ship. Set it on leaving port, and each day at noon (which you can tell from the sun) check the 'real' time on the clock. From the difference in the times you can easily calculate your longitude. The difficulty with this method at the time was that no clock could be relied upon. Differences in humidity, temperature and air pressure always made the clocks of the day run fast or slow. This is the problem that Harrison solved.

There were a couple of competing theories. They involved studying the positions of the moons of Jupiter, or the transit of the moon across the sky. Both these involved lengthy comnputations (over four hours, by a clever human 'computer'). They also relied upon clear skies, and in the case of the moon, were not even possible on some days of the month when the monn didn't appear.

This is all the science you really learn in 'Longitude'. The bulk of the story is the human interest side. The British Government of the day encouraged this problem to be solved by offering up a prize of £20,000 to whoever managed it to their specification. Harrison spent nearly 50 years of his life working towards this, and only finally won three years before his death at the age of 83 (on his birthday in fact)

There were many feuds with competitors who wanted Harrison to fail. Once of these, Nevil Maskelyne, was even appointed Royal Astronomer and made a member of the Board of Longitude during his struggle. It took intervention from King George III to finally force the full prize to be rewarded. This human story is of course interesting, but it takes up far too large a portion of what is anyway a very slim volume.

So, 10/10 Dava Sobel for making popular science more popular, but only about 3/10 for actually describing the science. There aren't even any good diagrams, or schematics of the clocks themselves, which I would have thought should be a prerequisite for a book of this sort.

Posted by se71 at March 10, 2006 10:27 AM


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