| Great Men: John Harrison | ||
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by David Finlay (27 Feb 03) Also in this series: John Harrison has been one of my favourite engineers since the day I first heard about him. As a previous article (Beauty And The Machine) has already explained, he devoted almost his entire working life to solving the problem of finding longitude at sea, something which had defeated the world's finest minds for centuries, and which was proving enormously costly in terms of money and lives as ships regularly crashed or got lost for weeks on the oceans. The longitude problem was such a big issue for so long that trying to solve it became a synonym for madness. Harrison achieved the goal by devising an almost zero-maintenance watch that remained sufficiently accurate - regardless of changes in temperature and atmosphere or the movement of the ship - to give a reliable comparison between local time and the time at the port the ship had left. To do this he had to become the world's top clockmaker, and he did so by a very curious route. He was born in Lincolnshire in 1693, which was not a good start. Lincolnshire had no clockmaking tradition to speak of in the late 17th century, and Harrison's first career was that of a carpenter. Somehow, though, he got into the clock business, building some very impressive pieces (a number of them still keeping time today) which were unusual in many respects. He had a carpenter's-eye view of how to make clocks work, and he made ingenious use of wood in the construction process to limit the need for lubrication. Harrison's work became truly ground-breaking when he started building his marine clocks. The clock now known as H1 was the best - and certainly the strangest-looking - that had ever been devised, but it did not satisfy its maker. H2 was better still. Harrison laboured for 19 years over H3, which moved the whole game several stages further on. Masterpiece In Miniature H4, the incredible watch completed in 1760, was a tiny jewel compared with the monster clocks Harrison had been building over the previous decades, and it appears to be a shocking repudiation of everything its predecessors stood for. In fact, Harrison had taken the best of what he had learned from the clocks, added a few more innovations, and compressed it all into a beautiful little package which kept astonishingly accurate time regardless of any conditions it might find at sea. In the splendid words of his biographer Dava Sobel, "he wrested the world's whereabouts from the stars, and locked the secret in a pocket watch." Harrison died in 1773. The vehicle now generally accepted as the first motor car was not seen until 112 years later. But in his search for the ultimate timekeeper Harrison had developed technology which was to be of great importance to the automotive industry. The clock to focus on in this respect is H3, referred to by Harrison himself (with considerable understatement) as "my curious third machine". As its gestation period suggests, this is an intimidatingly complex device. It did not completely solve the problem of maintaining accurate time regardless of the ship's motion, but it was able to deal with changing temperatures, and it included Harrison's most elegant approach to ensuring constant smooth running. In his earlier clocks, Harrison had made bearings out of lignum vitae, a self-lubricating form of wood. It was exactly the sort of thing that a brilliant carpenter would have thought of, rather than a trained clockmaker. By the time of H3 his carpentry career was a distant memory, and he developed a metal device that was even more extraordinary - the caged roller bearing. Keeping Our Wheels In Place This new bearing worked so well that it found applications throughout the engineering world. Every car in the world is fitted with a development of it. Wheels are held in place by tapered roller bearings, which give lateral control that Harrison's bearing could not (and, in the clock, didn't need to). But the principle is exactly the same. Our cars run on wheels which are able to turn round millions of times with perfect reliability because of a piece of equipment that a Lincolnshire carpenter invented in the mid 1700s when he was trying to build the world's most accurate clock. H3's phenomenal ability to tick at the same rate regardless of temperature - which had scuppered earlier marine clocks - was the result of another innovation. Previously, Harrison had created gridirons made of two different metals which reacted differently to temperature and compensated for the tendency of the clocks to run fast or slow. These gridirons were effective, but they were also clumsily large. In H3, Harrison achieved the same effect far more neatly by riveting together rods of brass and steel and creating what is now known as the bi-metallic strip. Once again, the new technology was quickly taken up in apparently unrelated areas of engineering, and became commonplace in cars. For example, automatic chokes on engines using carburettors were adjusted by coiled bi-metallic strips which changed shape to a predictable extent as they reacted to changes in water temperature. This was still relevant up until ten years ago, when the compulsory fitment of catalytic convertors forced a universal move from carburettors to fuel injection. But bi-metallic strips are still used as the basis of nearly all thermostats in houses, factories, cars and indeed any environment in which temperature control is an issue. One result of this is that you can drive for many years without devoting a moment's thought to how hot or cold your car's engine is running. And you can do this thanks to the efforts of the shy, modest, incredibly industrious John Harrison, one of the finest engineers there ever was. Further reading Also in this series: |
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