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

The Board of Longitude took months to consider the evidence from the second test of Harrison’s H-4 sea clock. Based on its ability to determine longitudinal accuracy to within 10 miles—three times more precise than required—the clock ultimately won unanimous approval as the winner of the prize.

The Board then tried to renegotiate the terms of the award. It offered the full amount only if Harrison turned over all his sea clocks, complete descriptions of their workings, and two copies of the H-4. Early in 1765, Maskelyne succeeded Bliss as Astronomer Royal, joined the Board, and promptly argued that his much slower celestial method should be the winner. Parliament, meanwhile, amended the Longitude Act specifically to put pressure on Harrison.

Though angry and resistant, Harrison finally relented. He turned over the clocks’ drawings and descriptions, and a distinguished committee of watchmakers, mathematicians, a scientific instrument maker, and Nevil Maskelyne attended a demonstration at Harrison’s studio. For six days, the inventor showed and explained the timepieces. The committee approved. Harrison began to construct two H-4 replicas. That fall, he received the first £10,000 of his prize.

Maskelyne sought a grant to develop a tome filled with “prefigured data” to help sailors speed up their longitudinal calculations, reducing the effort from four hours to half an hour. His “Nautical Almanac and Astronomical Ephemeris” was a success (134), and the lunar tables were updated continuously until 1907.

The Board decided to subject Harrison’s clocks to more tests—10 months of them at the Greenwich Observatory. Maskelyne would be in charge. His couriers retrieved the four clocks from Harrison’s London residence, dropping one in the process, and transported three of them by wagon over rough roads. H-4, at least, traveled by boat to Greenwich.

On his second voyage to the South Seas in 1772, Captain James Cook distributed sauerkraut to the sailors. This preserved food, chock-full of vitamin C, kept the crew healthy and well able to perform the many scientific experiments the mission required. Among these were comparisons between an expert replica of Harrison’s H-4 clock and the lunar distance method. Cook, who could compute longitude both ways, praised the sea clock.

At Greenwich, the original H-4, under the watchful eye of its enemy Maskelyne, suddenly and mysteriously became quite erratic, its timekeeping off by as much as 20 seconds per day. No account was noted of damage the clock had suffered, possibly during its dismantling and demonstration. Maskelyne concluded that the timepiece “cannot be depended upon to keep the Longitude within a degree in a West India voyage of six weeks” (141).

Harrison replied with a pamphlet that called into question Maskelyne’s test methods, his choice of witnesses, and his placement of the Watch in the hot sun while his thermometer resided quietly in a shaded corner.

Harrison completed a required copy of H-4 in 1770. Though less ornate, H-5 maintained the same standards as its predecessor. The watchmaker, now in his 70s, despaired of completing a second copy or ever seeing himself vindicated. His son William wrote to King George III in 1772, explaining his father’s situation and asking for help. The king assented and placed H-5 in his private observatory for testing. The watch behaved badly until the king remembered he had stored magnetic lodestones in the same room. When the stones were removed, the watch performed brilliantly, testing accurately “to within one-third of one second per day” (148).

The king took up the Harrisons’ cause. In 1773, Parliament heard a debate on the subject. At the king’s suggestion, John Harrison dropped his legal objections and appealed for simple decency and fairness. This approach worked: Parliament voted him a separate award of £8,750. The legislative body also reworked the Longitude Act, but this made it even more difficult for anyone to win the prize.

Captain Cook returned to England in 1775 and lauded the H-4 replica watch crafted by Harrison ally Larcum Kendall. Aside from helping to determine correct longitude during the voyage, Kendall’s “K-1” watch permitted the captain to make accurate maps of South Sea islands.

Cook brought K-1 with him on his third voyage, where he ran into trouble with native Hawaiians, who killed him. Strangely, “Almost at the instant the captain died in 1779, according to an account kept at the time, K-1 also stopped ticking” (151).

Toward the end of Harrison’s life, other watchmakers began to try their hands at making chronometers styled after the H-4 timepiece. As these watches became available, England’s control of the seas solidified, adding to the growth of the British Empire.

Mass production of precision clocks at first foundered on their sheer expense. Kendall produced K-2, a less accurate but much cheaper version of Harrison’s H-4 masterpiece. The watch had many adventures, including a stint on the HMS Bounty; after that ship’s crew famously mutinied, the watch spent time on their Pitcairn Island hideaway. Kendall’s third watch omitted the diamonds from the movement and was cheaper still. It rode on Cook’s third and last voyage.

Watchmaker Thomas Mudge built three beautiful chronometers and managed to obtain £3,000 in reward money from the Board of Longitude. Watches used his lever escapement until the mid-20th century. It was John Arnold, though, who produced several hundred high-quality chronometers by farming out much of the work to others and carefully finishing the watches himself. Arnold’s 1779 pocket chronometers were accurate to within three seconds a day, and his many innovations simplified and miniaturized Harrison’s Watch.

Arnold and watchmaker Thomas Earnshaw got into an extended legal battle over various inventions by Earnshaw that Arnold copied. Beginning in 1803, Maskelyne took a liking to Earnshaw’s chronometers and championed them. In 1805, the Board of Longitude awarded both Earnshaw and the estate of Arnold £3,000 for their improvements in watchmaking.

Competition and innovation drove down prices to what today would be a few thousand US dollars, and the 1780s saw a flood of chronometer purchases by naval officers. The British Navy also stockpiled the new chronometers for its captains to borrow. By 1815, 5,000 high-precision timepieces were in use. Many ships had several chronometers aboard: HMS Beagle, the ship on which Charles Darwin traveled in 1831 to the Galapagos Islands, boasted 22 timepieces. By the time it dissolved in 1828, the Board of Longitude was a tester and assigner of chronometers to naval vessels.

Astronomer Royal Maskelyne put the starting meridian, or zero degrees longitude, at his observatory in Greenwich, and soon mariners were recording their positions in degrees east or west of Greenwich. Sailors eventually used Maskelyne’s almanacs of lunar positions mainly to verify their ships' chronometers. In 1884, 26 nations convened in Washington to make Greenwich the location of the prime meridian. The French, who had their own observatory in Paris, balked at first but finally accepted the British location.

Each day begins officially at midnight in Greenwich; all nations set their clocks a regulated number of hours ahead of or behind Greenwich Mean Time (GMT). In 1833, the Observatory began a daily practice of raising a large red ball on a poll at Meridian Courtyard and dropping it at precisely 1:00 pm, allowing ships at harbor in London to set their clocks without referring to Maskelyne’s complex lunar tables. In today’s world of atomic clocks—including one at the Observatory—and satellite signals, the red ball is largely ceremonial.

Harrison’s first clocks, H-1 through H-3, had been in storage at Greenwich since 1766, excluding a brief cleaning in 1836. In 1920, former Royal Navy Lieutenant Commander Rupert Gould retrieved the three clocks and H-4 and spent 12 years returning the devices to their former glory. His detailed notes explain the timepieces better than Harrison’s own descriptions. Today, the first three clocks are wound every day and remain on display next to H-4, which is preserved silent, unmoving, and protected from wear.