The Longitude Act of 1714. The desperate struggle for precision.

John Harrison's Marine Chronometer - H4

Timepieces don't really keep time; they just keep up with it, if they're able.

-Dava Sobel, "Longitude"time

Finding a precise timekeeping instrument was a matter of life and death.
Mans struggle to determine longitude spanning four centuries, fueled the inventions of precise timekeepers. Timepieces which lost time, lost men at sea, as they were unable to calculate their location and wandered among invisible lines of longitude weaving in and out of degrees.

The 1600's and 1700's were perilous. Fleets of ships' sent out by hungry sovereigns on world exploration and to trade silks and spices were unable to determine their location. Some found land, some were too late spilling their scurvy riddled sailers onto an unmarked shore, others wandered aimlessly 20 degrees off coarse, some sunk in dark unforgiving waters. On October 22, 1707, four British Men 'O War sank just off the Cornish Coast. 2000 men were lost. In 1714, The British Parliament , aggravated by this obviously needless catastrophe, passed the Longitude Act: A huge sum of money would be awarded to anyone who could invent a way to determine the precise longitude of a ship's location to within less than one degree.

Latitude, the parallel lines circling the earth, mapped by Ptolemy in AD150. The equator at zero-degrees , derived from astronomers observing the sun, moon and planets passing directly overhead and the Tropic of Cancer and Tropic of Capricorn, assigned by the sun. Ships following the lines of latitude would guide the vessel by the length of the day or by the height of the sun or the heavenly stars that shone in the nights sky. Christopher Columbus"sailed the parallel" on his 1492 journey.

Lines of latitude are governed by nature - the sun, moon and stars; however, the lines of longitude move like waves on the waters edge. Lines of Longitude are changed by time. The longitude are lines that thread from the North Pole to the South Pole.

To know ones Longitude at sea, one must know the time at home port and at the same time knowing the time on ship. Once the time difference is known, the difference by degrees is known and thus the crucial longitude. The world spins on it axis 360 degrees in a 24 hour period thus in one hour it turns 15 degrees. If the navigator resets his ship's clock local at high noon, and refers to his clock representing time at the home port, every hour difference translates to 15 degrees from the home port. A precise watch was imperative to know the ships course and save it from potential destruction.

Sir Isaac Newton weighing in on the timekeepers approach to Longitude:

One method is by Watch to keep time exactly. But, by reason of the motion of the Ship, the variation of Heat and Cold, Wet and Dry, and the differences of gravity in different latitudes, such a watch hath not yet been made. And he implied - not likely to be either.

The Longitudes Act was passed to solve the puzzle of Longitude. Many great watchmakers, craftsman, astronomers and inventors dedicated their entire lives to come up with a solution. Galilao used the moons of Jupiter . Huygens, one of the first great horologists, crafted a marine timekeeper which used a pendulum; however the great rolling waves confounded its accuracy and changes in temperature and humidity thickened its oils. Huygens, then patented the spiral balance spring as alternative to the pendulum.

Discovering the Longitude, even with rewards of huge sums of money (20,000 Pounds translated into one million Dollars today) became synonymous with achieving the impossible, and the brunt of many jokes. Jeremy Thacker of Beverly, England developed a marine timekeeper which he coined the chronometer - a term adopted by horologists and still used today. The chronometer was placed in a vacuum, to protect the watch from atmospheric pressure and humidity, and had implemented a pair if winding rods to keep the machine going while being wound. However, he did not account for room temperature which exerted a huge influence on the accuracy of the watch. Although a success in its own right, the constant supervision needed to ensure the chronometer would maintain accurate time as well as the loss of six seconds a day was the chronometer undoing. The Board of Longitude did not approve his chronometer,
Sir Isaac Newton grew impatient , his Universal Law of Gravitation had gained much interest; however; determining longitude still remained a mystery. In 1721 Sir Isaac Newton wrote:

"A good watch may serve a recconing at Sea for some days and to know the time of a Celestial Observation: and for this end a good Jewel watch may suffice till a better sort of Watch can be found out. But when the Longitude at sea is once lost, it cannot be found again by any watch." Sir Isaac Newton died in 1727 and missed the Longitude prize that was awarded 40 years later to the self-educated maker of a large pocket watch...

JOHN "Longitude" HARRISON

Born: March 24, 1693
1713: Built first pendulum clock constructed entirely of wood.
1722: Built Tower Clock in Brocklesby Park running for 286 years. No oil is needed as the clock is carved from lignum vitae, a tropical hardwood that exudes its own grease.
1725-1727: Built two long-case grandfather clocks utilizing his own invention - the grasshopper escapement.
1730-1735 developing his first Chronometer the H1, at 75lbs it still works with daily winding at the National Maritime Museum in Greenwich. The H1 set sail and returned with triumph of having kept impeccable time. Harrison on the other hand was not much pleased with his first attempt, and told the Longitude Board he needed to improve on the H1. Thus for the next two years he set about making the H2 which never set sail as he disregarded this watch too, as a result of a series of imperfections. Although the H2 had the backing of the Royal Society and had faired very well in tests of temperature, John Harrison became closeted in his workshop working on the H3,
For the next 20 years he concentrated on the watch, those that surrounded John Harrison could not understand what could be taking him so long. No one suggested he slept on the job. John Harrison never slept on the job he had created the H3 with 753 separate parts including a bi metallic strip which compensated for any temperature change as well as caged ball bearings - an anti friction device still used in almost every machine with moving parts. Although this edition had shrunk dramatically since the H1 it was still too large.

By chance Harrison met John Jeffreys, a freeman with The Worshipful Company of Clockmakers, who in 1753 made Harrison a pocket watch. According to Harrison's specifications, Jeffrey fitted the watch with a tiny bi metallic strip to keep the watch precise in hot or cold weather. In addition, this watch kept ticking while being wound. Some horologists today consider the Jeffreys timepiece as the first true precision watch.

Harrison set to work on the H4 a much smaller version than the first two chronometers and resembling an over sized pocket watch. Harrison was awarded the prize, as the H4 kept time, three times more than the Longitude Act demanded. However, the Longitude Board kept changing the rules, and now Harrison ,who was already in his mid-seventies was required to build two more watches like the H4 , and an additional year of testing. Although this watch kept time it was too complex for ready reproductions and very expensive. Thus his watch was never widely used by navigators at that time.


Although in his life time, he did not see the real fruits of his labor, he did make a large contribution to the world of horology. After Harrison's success with the H4, marine timekeeping boomed in a nation surrounded by water. It is said as a result of Harrison's advancements in timekeeping, he spearheaded Britain on successful voyages with the aid of chronometers thereby leading to the creation of the British Empire.

Harrison successfully crafted a watch that kept time with precision even in less than perfect climates. Such precision Sir Isaac Newton had deemed impossible.

Adapted from "Longitude" by Dava Sobel