He had the whole world in his clock hands

THIS YEAR is the tercentenary of the birth of one of my heroes, a man whose work I do not understand in any technical sense although its beauty, precision and usefulness have delighted me for 20 years. His name is John Harrison.

I doubt if many people other than horologists will have heard of him; yet this self-taught clockmaker, using nothing but invention and his own hands, designed and built the most important clocks of his time. He made navigation safe, for the accuracy of his timepieces is such that, more than 200 years later, charts based on them can hardly be improved.

Born in 1693, the son of a carpenter, John Harrison never served an apprenticeship but taught himself first how to repair and then how to build clocks. His first efforts, as you might expect, were made of wood. Why he should have turned to clock-making nobody knows; might as well ask why a glove-maker's son wrote plays. Genius will out.

In 1714, the year Queen Anne was succeeded by George I, the government appointed a committee to consider the vital question of longitude at sea. Men and ships were being lost because the position of the ship could not be accurately charted. Longitude could be found if a ship's clock kept the precise time in the port of departure. It was easy to calculate time (from the stars, I assume) at the ship's position; the difficulty was to know the time left behind.

This was thought by the best authorities, including Sir Isaac Newton, to be impossible because of the vicissitudes that clocks suffered during long voyages, from changes in temperature and the motion of the waves. The committee recommended offering a prize of pounds 20,000 - equivalent to a million pounds today - for 'any generally practicable and useful' method of finding longitude at sea.

Between 1730 and 1759, Harrison built three 'sea clocks' (marine chronometers, to use their modern title), known prosaically as H1, H2, and H3. They are all on show in the splendid new galleries at the Old Royal Observatory, part of the National Maritime Museum at Greenwich, and by pressing a button in the side of the case you can listen to their lilting musical ticking.

Harrison himself came to this observatory in 1730 to see Edmund Halley, Astronomer Royal, who recommended him to George Graham, the greatest scientist and clockmaker of his day and thus an extremely busy man. Graham was besieged by aspirants for the pounds 20,000 prize.

Harrison later recalled: 'Mr Graham began very roughly with me (but) he became at last vastly surprised by the methods which I had chosen to take.' He records that he arrived at 10am and was still with Graham at 8pm, having been given not only dinner, but also a loan towards his costs.

Being 'without the constraints of a formal education', Harrison went back to first principles. Graham saw immediately that Harrison's ideas were revolutionary: first, because his chronometers required no lubrication - and clock oil is the Achilles' heel of all clocks. Instead of inventing a better oil, he invented moving parts for a clock that didn't need oil. Second, the balances in Harrison's chronometers were interconnected so that one compensated for the other and they were unaffected by the movement of the waves.

His first timepiece took six years to construct, the second only two. H3, containing 753 separate handmade parts, took 17 years, from 1740 to 1757. When it was finished, Harrison applied to the Board of Longitude to judge whether he had won the prize.

While awaiting their verdict he had the most revolutionary idea of all. For a portable timekeeper to be truly accurate on long voyages (such as Cook's to the South Seas) Harrison realised that what was needed was not a sea clock but a watch. It had been judged impossible to invent a clock that worked at sea. A marine watch seemed ludicrous.

Harrison set to work regardless and made H4, which is a beautiful watch, slightly more than 5in in diameter. It recently featured on an exquisite set of stamps. Last Saturday, the curator of horology - a beguiling young enthusiast called Jonathan Betts - took this watch out of a safe and allowed me to look at it. I saw it as close as my typing fingers are to my nose. It is a marvel of delicacy, extraordinary in detail, perfect in execution. I was awestruck, as though I had been shown Hamlet in manuscript.

Harrison decided to submit this watch, H4, for trial and in 1761 his son, William, set sail with it from Portsmouth on board HMS Deptford. On reaching Jamaica more than two months later, H4 was found to have lost five seconds: an error equal to less than one mile and incomparably better than anything previously achieved.

But governments then, as now, were dilatory and reluctant to pay up. The committee claimed this trial was insufficient, although after a second had proved that the first was no fluke, it did, grudgingly, award him half the prize money.

Finally, when the committee had run out of excuses and John Harrison was 80, and after the personal intervention of George III, he was paid the remainder of the money. The great clockmaker died three years later. I hope he was a happy man.

The story does not end here. The Harrison chronometers owe their continued existence to the skill and devotion of a retired naval commander called Rupert Gould who, in 1920, found them in a dilapidated state. After 12 years of painstaking labour, he restored them to the condition in which they can be seen today, in full working order, with audible ticks that sound like the music of the spheres.

When asked whether this immense task had been worth it, Lieutenant Commander Gould replied: 'A man is truly great who makes the world his debtor. And if we apply that criterion to the work of John Harrison, we can come to only one conclusion - that he was a truly great man.'