Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time

Clockmaker John Harrison was born in 1693, learned woodworking from his father, taught himself science by studying the works of Newton and other natural philosophers, and learned about clocks by building three of them. The works of these clocks were made entirely of wood, and their cogs were nearly unbreakable. Harrison also played musical instruments, rang the local church’s steeple bells, and directed the choir. Despite his mechanical brilliance, he had trouble expressing himself: His longest sentence, written late in life in a book that explains his dealings with the Board of Longitude, goes on for 25 pages.

Harrison married twice. His first wife, Elizabeth, died when their son, John, was only six. His second marriage lasted 50 years and produced William, who was later his father’s “champion” during the decades of struggle to win the prize, and Elizabeth, about whom little is known.

Harrison built his first clock tower in 1722; it still works today. To deter rust, Harrison avoided metal, instead using self-greasing tropical hardwoods or specially selected oak. Elsewhere, to solve the problem of pendulum-clock accuracy, Harrison and his brother James combined alternating strips of brass and steel, which “counteracted each other’s changes in length as temperatures varied” (71). John also invented a friction-free mechanism. The Harrisons’ clocks were accurate to within one second a month, 60 times better than any competing timepiece.

Pendulums, though, wouldn’t work properly at sea, so John Harrison set out to solve the longitude problem with a new type of clock.

In 1730 Harrison visited Edmund Halley, director of the Royal Observatory, with plans for a sea clock. Though skeptical of mechanical solutions to the longitude problem, Halley was impressed, and he introduced Harrison to watchmaker George Graham, who became Harrison’s patron.

The Harrison brothers developed their first sea clock, the all-brass “Harrison’s No. 1” (77), and presented it to Graham in 1735. He forwarded the invention not to the Board of Longitude, but to the Royal Society, which recommended a trial run. In 1736, the clock got its test aboard the naval vessel HMS Centurion on a week-long run from London to Lisbon. Unfortunately, the ship’s captain died suddenly at Lisbon before writing up his impressions. On the return trip aboard the HMS Orford, the clock predicted the ship’s location accurately, whereas the commander’s reckoning was 60 miles off. Impressed, the commander wrote up a positive affidavit.

The following week, the Board of Longitude met to consider Harrison’s new clock. Harrison, however, argued for time and money to make the clock even better. The Board agreed. Five years later, Harrison returned with a greatly improved clock, H-2, which withstood elaborate tests and warranted a sea trial. Harrison, however, argued that this second clock still wasn’t up to his own standards. The Board relented, and Harrison went back to his studio, now in London, and toiled for 20 years on the third sea clock.

Graham, meanwhile, borrowed H-1 and exhibited it at his own shop, where dignitaries came to ogle at its precise timekeeping.

While John Harrison perfected his sea clock, others were improving the system of gauging longitude by the stars. Using a new instrument called a reflecting quadrant and a later improvement called a sextant, sailors would make extensive observations of celestial objects. They then would consult ephemerides—their tables filled with data gleaned over 60 years by astronomers John Flamsteed and Edmund Halley—of the position of the moon against the background of stars, or of its position relative to the sun, at any given moment throughout the year. This process could take hours even on a clear night, but by comparing the difference between the recorded time of the celestial event in the skies above Paris or London and the local time of the ship at sea, sailors could compute their longitude.

When Halley died in 1742, James Bradley became Astronomer Royal at Greenwich, where he improved the star catalog, discovered the diameter of Jupiter, and perfected the calculation of the speed of light. However, he ignored Harrison’s invention despite having been an early supporter of it.

Bradley discovered a new, improved method of predicting the moon’s position. This method came from German mapmaker Tobias Mayer and mathematician Leonhard Euler, who worked out an elegant equation for the relationships between the Earth, moon, and sun. Lunar tables became so accurate that, beginning in 1757, seagoing tests were held to determine whether the ephemerides rated the longitude prize. The Board gave out grants and small awards, but the big bounty remained out of reach.

With his son William, Harrison spent nearly two decades perfecting the 753 parts that made up his latest sea clock, H-3. The new clock contained improvements in bi-metal temperature control and ball bearings that reduced friction. The device also was much smaller and lighter than its two forebears. The Board of Longitude waited patiently, extending Harrison’s grants while he and his son toiled on the project. The Royal Society awarded John the Copley Gold Medal and invited him to join their group; he campaigned instead for William to become a member, and the Society admitted him.

John commissioned a watchmaker, John Jeffreys, to construct a pocket watch to strict specifications. This timepiece, which still exists today, was vastly more accurate than other pocket watches of the era: “Some horologists consider the Jeffreys timepiece the first true precision watch” (105). The smallness and portability influenced the design of H-4, which came in at a mere three pounds and five inches in width. Harrison perfected H-4’s movement with diamonds.

Ornately crafted, “the Watch” remains a masterpiece. Its innards, carefully miniaturized, had to be cleaned and oiled every three years. Today it’s displayed alongside its frictionless siblings H-1, H-2, and H-3 at the National Maritime Museum in London, but H-4 is no longer permitted to run, lest its mechanism wear out.