Sir Cloudesley Shovell and the Longitude Act

Article by Audrey Lappin

From cabin boy to Admiral of the Fleet, Sir Cloudesley Shovell rose to high rank in the Royal Navy and proved brave and active in his country’s service. His death and the wreckage of his four-ship fleet off the Isles of Scilly on 22nd October 1707 was a tragic event. Believing themselves to be safely off the coast of Brittany, they perished on the rocks of south west England. This disaster capped a long story of seafaring in the days before sailors could establish their longitude position and the dread disease of scurvy carried off many seamen when they could not restock fresh food. In addition to the human suffering, ignorance of longitude had a severe economic effect. Ships were confined to a few narrow shipping lanes where they fell prey to pirates and enemy ships.

The disastrous wreck on the Scillies when Shovell died thrust the longitude problem into the forefront of public concern. Parliament passed the Longitude Act of 1714 in which a prize of £20,000, comparable to £2.5 million today, was promised for a solution to the problem. Longitude represents the location of a place on Earth east or west of an established line running north-south. The north-south line is called the Prime Meridian, which was fixed at Greenwich, England. Earlier methods to determine longitude attempted to compare local time with the known time at a given place and relied on astrological observations. At that time, the position and movement of the moon and stars were not fully understood and no accurate instrument existed for measuring lunar distance from a ship.

Amongst the many people who applied themselves to solving the problem was John Harrison, the eldest of five children of a carpenter. Largely self-educated, John learned woodworking from his father. He constructed his first pendulum clock, almost entirely from wood, before he was twenty. In 1722, he completed a tower clock where parts normally requiring lubrication were carved in lignum vitae (the wood of life), which exudes its own grease. Harrison avoided using iron or steel in the clockwork to prevent rusting – instead he substituted brass. He developed a later innovation in constructing a pendulum: alternating strips of different metals, which avoided the problem of expansion and contraction and the consequent effect on the measurement of time.

In 1730 Harrison designed a marine clock to compete for the Longitude Prize and went on to build his first sea clock, which performed well in sea trials. Two more versions were produced in the next seventeen years. Around 1750 Harrison changed the idea of a sea clock, realising that a watch- sized timekeeper would be more successful and more practicable. He proceeded to design and make the world’s first successful maritime timekeeper that enabled a navigator to assess accurately his ship’s position on longitude. It was a revolution in navigation at sea.

Harrison had to enlist the help of George III to petition for the prize but never received the official award, although he received monetary amounts from the Board of Longitude during the course of his work. He died in 1776, and was buried in the graveyard of St John’s Church in Hampstead.