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When the clerk at the Board of Longitude in London saw Thomas Earnshaw’s bill, he took a deep breath and totted up the figures carefully. For one regulator clock, £89 5s. A wooden stand and packing case, another £43. Add one pocket chronometer, a “journeyman clock” and some repairs to a “larum clock” and the total came to £195 13s 6d. This was a lot of money at the close of the 18th century. But then Earnshaw made some of the finest timepieces in England. These were commissioned for George Vancouver’s voyage to survey the Pacific coast of North America – a triumph of navigation that relied on accurate timepieces.

The regulator (above) was a vital part of the expedition’s equipment, allowing Vancouver to check the accuracy of his chronometers and so calculate longitude with reasonable certainty. In fact, the regulator kept such perfect time that after Vancouver had finished with it, the board sent it to sea again. This time it sailed with Matthew Flinders and HMS Investigator, the first ship to circumnavigate Australia.

BY THE time young Matthew Flinders set sail for Australia in 1801, navigation had become more science than art. The old problem of calculating longitude was pretty much solved, and although the technology that had solved it – the marine chronometer – was still regarded as experimental, it was rapidly gaining acceptance as the best and quickest means of fixing position.

Almost three decades had passed since Parliament belatedly awarded John Harrison the prize for finding a way of calculating longitude – by designing a clock that kept accurate time at sea. With a timepiece that could withstand the rolling of a ship and tolerate large fluctuations in temperature, navigators could work out where they were by comparing local time with the time at the Greenwich meridian. For every hour’s difference, they knew they were another 15 degrees east or west of Greenwich.

Harrison’s chronometers were marvellous things, but were so complicated there was no prospect of mass production. Within a few years, the London clockmakers John Arnold and Thomas Earnshaw had designed more practical chronometers. But even their best weren’t perfect. During a long voyage, they invariably gained or lost time, drifting ever further from Greenwich Mean Time. No one was sure why. But that didn’t matter: if you knew how many seconds the chronometer was out by, you could adjust your calculations. This meant checking the “rates” of the chronometers with a regulator – a clock you could rely on absolutely.

In 1791, when the British government sent George Vancouver to survey the Pacific coast of North America, the Board of Longitude supplied him with five chronometers. One was a copy of Harrison’s finest, which had already been round the world with James Cook. There were three Arnold chronometers and one by Earnshaw. The Board also commissioned a regulator from Earnshaw – a large pendulum clock with split-second accuracy. This had a jewelled mechanism to reduce friction and a pendulum with nine brass and steel bars designed to cancel out the expansion and contraction caused by changes in temperature.

Vancouver left England with the ships HMS Discovery and Chatham and two of the chronometers, reaching the north-west coast of America a year later. The clock and three more chronometers followed in the supply ship HMS Daedalus. They were accompanied by the 22-year-old astronomer William Gooch, who was to help with the astronomical readings and calculations. Like Cook, Vancouver was wary of relying entirely on chronometers and planned to check his calculations by observing lunar distances, another new, but more time-consuming method of determining longitude.

The clock reached Vancouver safely. The unfortunate Gooch didn’t. When the Daedalus finally caught up with Vancouver, both its captain and the astronomer were dead – murdered in Hawaii. Vancouver had lost his astronomer, but he now had three more chronometers, a regulator and a portable observatory made of a collapsible tent with a moveable roof.

As Vancouver’s boats surveyed the nooks and crannies of the coast, he made regular stops to set up the observatory on shore. For a week or more at a time, he and his officers would observe the Sun, Moon and stars, making far more accurate measurements than they could from the moving deck of a ship.

This was also a chance to check the rates of the chronometers against the regulator. At sea, a pendulum clock is useless, and the regulator remained stowed away. But after a few days ashore it kept perfect time. Vancouver calculated GMT by taking into account the rates his chronometers gained and then worked out his longitude using the average from the five chronometers.

From his four years of voyaging, Vancouver produced accurate charts for the whole north-west coast of America and ruled out the existence of a north-west passage linking the Pacific and Atlantic in those latitudes. He also proved the value of chronometers in charting unknown lands. Job done, he sailed home and sent the clocks and chronometers back to the Board of Longitude.

Earnshaw’s regulator didn’t stay in retirement long. In July 1801, it was packed up and placed aboard Flinders’s ship Investigator, bound for a survey of Australia. Flinders also had five chronometers, three of them from Vancouver’s expedition. Flinders and the Investigator worked slowly round the coast of Australia, producing for the first time a complete outline of the continent and charts that were still being used well into the 20th century. Like Vancouver, he landed at intervals, set up a temporary observatory and calculated his coordinates astronomically. He then checked the chronometers against the regulator and compared the figures.

Flinders’s voyage was hugely successful – until March 1803. The Investigator, now in the Torres Strait north of Queensland, was leaking like a sieve. Flinders abandoned the survey and headed back to Sydney – travelling west to complete his circumnavigation. By now it wasn’t just the ship that was in poor shape. Earnshaw’s clock was in a bad way too. The movement was rusting and cockroaches had colonised the interior. In Sydney, Flinders found a clockmaker to repair it; the Investigator, though, was condemned.

Flinders failed to find a new ship in Sydney and sailed for England on HMS Porpoise, hoping to persuade the Admiralty to give him another vessel to complete his survey. He left the regulator in Sydney to be sent on later. Things now took a marked turn for the worse. The Porpoise was wrecked on the Great Barrier Reef. Flinders made it back to Sydney in an open boat to organise a rescue – and returned with three ships. He then made his really big mistake. With a handful of volunteers, he headed home to England in the tiny schooner Cumberland, hoping to make a few extra observations in the Torres Strait en route.

Flinders acknowledged his ship was “exceedingly crank” – but by the time he reached the Indian Ocean it was so unseaworthy, he knew it would never get him home. In desperation he diverted to Mauritius – a French possession. He was promptly arrested as a spy and was kept prisoner for six and a half years.

Earnshaw’s regulator had better luck and arrived safely back at the Board of Longitude. In 1993, it came up for auction at Sotheby’s and was snapped up by Sydney’s Powerhouse Museum – a reminder of the greatest voyage around Australia.