Navigators and mariners owe a debt to English clockmaker John Harrison

FOR centuries navigation and travel by sea was diabolically risky. Eventually English carpenter turned clockmaker John Harrison (left) developed the first marine chronometer which helped shape the world we know today.

John Harrison, the inventor of the marine chronometer, in a 1767 portrait by Thomas King.

FOR centuries sailors used the stars, land sightings, currents, intuition and observation to establish their position at sea. They were neither a precise nor reliable means of navigation, which made travel by sea diabolically risky.

The thirst to expand the known world drove a centuries-long quest to find a better method of navigation.

The answer would eventually come in the form of an English carpenter turned clockmaker whose initiative helped pave the way for the age of exploration which shaped the world we know today.

John Harrison, who, with little formal training as a clockmaker, developed the first marine chronometers that were accurate and reliable enough to allow navigators to determine their longitude — how far east or west a ship had travelled.

Some of those clocks are on display as part of the exhibition Ships, Clocks And Stars which opens today at the Australian National Maritime Museum (anmm.gov.au).

Ships needed to know the latitude and longitude of their position to prevent them steering off course or bumping into land. Ancient navigators had worked out that latitude — how far north or south a position is of the equator — could be determined by measuring the angle of the sun or a star to the horizon at their highest points in the sky. The angle changes the further north or south a person is.

Carpenter and self-taught clockmaker John Harrison.

But working out longitude was much harder. Most early navigators relied on dead reckoning, making estimates of distance travelled from a fixed point by measuring the speed of the ship. This was done by dropping over the side a rope tied to a log, with knots tied in the rope at set lengths. The number of knots that passed over the gunwale (the rail) of the ship over a set time (measured by an hourglass) would give a rough idea of the speed of the ship. These would be recorded to give some sense of how far the ship had travelled, giving us the maritime terms “ship’s log” and “knots”.

In 1659 Flemish cartographer Gerardus Mercator published a map showing the world divided into lines of latitude and longitude, imaginary lines that navigators could use as points of reference. But determining which line of longitude a ship had travelled to was still largely beyond seamen.

In theory it could be done by knowing the time at a fixed point — for example the observatory at Greenwich near London — and comparing that to local time by taking a reading at noon when the sun was at its highest point.
If the sun reached noon earlier than it did at Greenwich, then the ship was west of that point, and if later, then it was east. Each hour equated to 15 degrees of longitude.

An error in determining correct longitude caused four British naval ships to run aground at the Scilly Isles, southwest of Land’s End, in 1707, with the loss of about 2000 men including Admiral of the Fleet, Sir Cloudesley Shovell. In 1714 the British government passed the Longitude Act offering a reward of £20,000 for anyone who could devise an accurate method of determining longitude.

Born in 1693 in Yorkshire, Harrison had long been obsessed with making an accurate timepiece. He realised a clock to determine longitude would need to be able to function aboard a rocking ship, in different temperatures and climates. Harrison took five years to produce his first timepiece specifically for the longitude reward in 1730. H1 as it was known, contained mechanisms to compensate for temperature and ship’s motion. It performed well enough for Harrison to be granted £500 from the Longitude Board to develop it.

The chronometer invented by John Harrison in 1737, which enabled mariners to chart their longtitude.

He perfected his device with H4, a watch with a hand crank that was only 13cm in diameter and presented to the board in 1765. But despite positive tests Harrison struggled to get his reward. It was not until 1772 that he was given £10,000 for his device and a further £8000 in 1773 after a meeting with the king, but Harrison was never officially awarded the prize.

At about the time he created his clock a complicated method using sightings from the moon was also devised, which is what Lt James Cook used on his first voyage of discovery aboard the Endeavour.

For his second voyage he took copies of Harrison’s clocks made by watchmaker Larcum Kendall, the original considered too precious to go to sea. Cook praised the accuracy of the clocks based on Harrison’s design. On his third voyage he took a simplified version of the clock, again made by Kendall. This would later be used by Matthew Flinders on his voyages around Australia.

Cook later wrote: “I would not be doing justice to Mr Harrison and Mr Kendall if I did not own that we received very great assistance from this useful and valuable timepiece.”

Originally published as Navigators and mariners owe a debt to English clockmaker John Harrison