Faculty of Pure and Applied Sciences Newsletter

In January 2004 a monument commemorating the first test, in January 1762, of a chronometer that could accurately measure longitude at sea was unveiled at the home of the Flamstead Heritage Society in the Port Royal Mountains of St Andrew.

In unveiling the monument, the Minister of Commerce, Science and Technology, Phillip Paulwell, commended the Society for encouraging heritage tourism in the area. He also noted that the Society sought, through this event, to encourage creative developments in science and technology.

Noting the enormous strides in the technology used to measure longitude in the last two centuries, Minister Paulwell compared John Harrison’s chronometer with the geopositioning system now used to measure longitude which had earlier been demonstrated by Florin Ionica, Network Engineer at the Earthquake Unit of the Faculty of Pure and Applied Sciences, UWI.

Longitude is the distance east and west on the earth’s surface measured from a certain meridian or place, estimated in degrees. In this historic instance, Port Royal, Jamaica , was the place. Flamstead, named after the Royal Naval Observatory’s Flamstead House, was Port Royal’s naval lookout.

As Phineas Fogg belatedly discovered in Around the World in Eighty Days, for every 15 o that one travels eastward, the local time moves one hour ahead. Similarly, if one travels westward, the local time moves back one hour for every 15 o of longitude.

Therefore, if we know the local times at two points on Earth, we can use the difference between them to calculate how far apart these places are in degrees of longitude.

This idea was very important to sailors and navigators in the eighteenth century. They would measure the local time wherever they were by observing the sun, but navigation required that they also know the time at some reference point (e.g., Greenwich) in order to calculate their longitude.

Throughout the great age of exploration, sailors attempted to navigate the oceans using the stars and other imprecise means. This often resulted in disaster as voyagers lost their way.

Although accurate pendulum clocks existed in the eighteenth century, the motions of a ship and changes in humidity and temperature would prevent such a clock from keeping accurate time at sea.

To encourage a solution to this problem, the British Parliament passed the Longitude Act in 1714. The Act offered the then colossal prize of £20,000 for the invention of a machine that could measure longitude at sea.

The prize was eventually won by John Harrison, a joiner turned clockmaker who designed a chronometer named H4. This was the clock used in the 1762 trial.

The first test of this chronometer took place at Port Royal after it was sent on a three-month voyage from England to Jamaica on the ‘Deptford.’

The vessel arrived in Jamaica on January 19, 1762. William Harrison, John’s son, represented his father on the trip.

As a means of ensuring quality control and security, the clock was placed in a box with four different locks and four separate keys. The box had to be opened regularly so that Harrison could wind the clock. One key was kept by the captain, the second by John Robison, the representative of the English Board of Longitude, the third by Harrison, and the fourth by William Lyttleton, the Governor-designate of Jamaica, on his way to assume his post.

In Jamaica, Robison and Harrison visited a number of places, including Flamstead, Port Royal’s naval lookout, to find a suitable site to set up astronomical instruments to establish local noon.

On January 26, 1762, Robison and Harrison synchronized their watches to fix the longitude of Port Royal by the time difference between the watches. The experiment showed that H4 had lost only five seconds after 81 days at sea.

After the successful test in Jamaica, Robison and Harrison returned to England. There was another trial of H4 on a voyage to Barbados in 1764.

After much controversy and debate, the prize was eventually awarded to John Harrison.

LONGITUDE 1762