Art & Engineering

5. The Story of the mechanical Chronometer.

After heavy damages with high losses, traders and owners of merchant ships urged the English Parliament to allocate financial means in order to find, with the help of science and research work, a solution for the problem of determining the degree of longitude on the high seas. The solution would also automatically bring for them the supremacy of the seas. The English Parliament offered, for that time, the considerable sum of 20,000 pounds with the "Longitudinal Act" in July 1714. The degree of longitude was to be exactly determined up to a few tenths of a degree.

John Harrison, son of a carpenter from Yorkshire, was neither a studied astronomer nor a scientist, but an intelligent, skilled and gifted joiner, and simultaneously an enthusiastic mechanic who built his first grandfather clock out of self-lubricating wood "lignum-vitae". His first pendulum clock goes back to the years around 1720. The greatest problem of his pendulum clocks was the influence of temperature on the accuracy. He introduced the first temperature compensated pendulum made of brass and steel in summer 1730. In May 1736 Harrison tested his clock on a cruise to Lisbon. For the rough sea the clock, which he called H1, was not yet suitable. Harrison officially demonstrated the H1 after further improvements to the jury at the end of June in 1737. The chronometer showed only a deviation of one second within a month. Harrison was in good faith fobbed off with 500 pounds, he should build an improved, more seaworthy version. An antagonist of his chronometer-theory was Isaac Newton. Newton stated that clocks are in general not seaworthy due to the inertia force influences and believed the degree of longitude determination could only be derived from the stars constellations.

The H2 came into being 2 years and the H3 a further 19 years later. In 1759 Harrison waited in vain with his H3 for a test voyage. In the meantime he built the H4 as pocket-watch. At the end of 1761 the English admiralty gave permission for the 81-day see journey to Jamaica. On grounds of Harrison's age, the trip, and with that the looking after of the clock was handed over to his son William. In Jamaica on 19th of January 1762 it was found that the H4 had lost only 5 seconds. Nevertheless malicious clock opponents in the jury refused him the prize. They even confiscated his clock and construction plans, he had to build two more clocks of the model H4. After 5 years one clock was ready. His age and his health did not allow any more the building of one further clock. Not until some interventions and a visit to the King of England did the English Parliament grant him, passing by the jury, as a reward for his efforts 18,750 pounds. Most of John Harrison's mechanical clocks are still in operation today, they are characterized by a high reliability and accuracy. To build uniformly running clocks was one thing, to adjust them exactly another. In this respect the pioneering work of John Harrison should not fall into oblivion.

Almost three centuries later the digital satellite navigation system and the caesium atomic clock from Braunschweig, which in a million of years shows only a deviation of plus/minus one second, permit an extremely exact determination of the latitude and longitude of any place round the world.