It’s All Relative: Marine Timekeeping and Searching for Longitude

Every January, the first-year fellows of the Winterthur Program and several students in MA and PhD programs from the University of Delaware take part in British Design History: a three-week course on design and material culture with one week at Winterthur and a two-week field study in Great Britain. Traveling to cities including London, Stoke-on-Trent, and Bath, the students have an opportunity to study American Material Culture within a greater global context. Students’ posts in this section are centered on their experiences in England or working with British objects in the Winterthur collection.


The highlight of the 2018 British Design History field study for me was undoubtedly our visit to the Royal Observatory at Greenwich. The long-time home and office of Great Britain’s royally appointed astronomers, today it is both a museum about the Astronomers Royal and one of England’s most significant collections of clocks and marine chronometers. Curator of Horology, Rory McEvoy, walked us through the collection and introduced us to the 17th-19th century Astronomers Royal and the museum’s collection of incredible timepieces and scientific instruments.

A brick building with white stone cornices sits on top of a hill. The central portion shown is of the second floor double-door with windows on either side and a cupola on top of each corner. On top of the left cupola is the time ball. Two squared turrets are on either side of additional ground-level rooms.

Flamsteed House at Greenwich, the home of the Astronomers Royal and the now-location of the Royal Observatory museum. On the left side cupola is the time ball, installed in 1833 for mariners to set their chronometers before setting sail. While the time ball is currently undergoing restoration, it still rises everyday: halfway up its mast at 12:55, the rest of the way at 12:58, and then all the way back down at 13:00. Image taken by the author.


Today in our world of constant digital timekeeping and communication, it’s difficult to imagine a time when sailing across the Atlantic Ocean was one of the most dangerous and isolated jobs. Until the early 18th century, sailors navigated by the North Star and dead reckoning – approximating one’s location based on the sun’s known movements – to determine where they were in relation to both departure and destination. These methods were risky at best; an accident in 1707, wherein four British Royal Navy ships perished off the Isles of Scilly, was blamed on navigators’ inability to accurately determine the ships’ proximity to the rocks upon which they perished. Had the navigators properly understood their longitudinal position, the crews might have survived.

The image shows Earth with the continents of Africa, Asia, and Europe in gray on white oceans. Lines of longitude run from the North Pole to the South Pole, obscured beneath the globe. The Prime Meridian is a thicker blue line labeled as 0° with “WEST” and “EAST” to the left and right, respectively, and lines of increasing longitude emanating from the Prime Meridian in each direction, labeled in increments of 15°.

An image of a globe with lines of longitude. Merriam-Webster’s defines Longitude as “the arc or portion of the earth’s equator intersected between the meridian of a given place and the prime meridian and expressed either in degrees or in time.” For example, the longitude of the Winterthur Museum is expressed as 75.6037° W, meaning that number of degrees west of the Prime Meridian at Greenwich. Image courtesy of


This accident led to the Longitude Act of 1714. The new Board of Longitude provided financial incentive for inventors to develop a simple, accurate method to determine location on long voyages. John Harrison, a cabinet- and clockmaker, acquainted himself with then-Astronomer Royal Edmond Halley and quickly rose to fame through his innovative ideas regarding how to balance such a delicate instrument as a clock on a ship at sea.

Portrait of John Harrison (1693-1776). Half-tone by P.L. Tassaert after original portrait by Thomas King, 1767. Image courtesy of Wikipedia and the Science Museum of London.


The concept was relatively simple. Astronomers Royal had used the stars to keep British timepieces accurately ticking for centuries, but clocks and watches were incredibly vulnerable to motion and changes in temperature and pressure. Harrison realized that if he could create a clock stable enough to resist these factors while onboard ship, mariners could minimize their risk by more accurately determining both their local time and their longitudinal relationship to Greenwich. In 1730 Harrison presented his first design to Edmond Halley and secured funding to build his first model. Its first live test in 1736 was successful on the return voyage from Lisbon, and Harrison spent the next thirty years developing subsequent designs to improve accuracy and meet the Board’s demands for a transatlantic voyage.

John Harrison’s first, second, and third designs made in reality: H1, H2, and H3. Images courtesy of the Royal Museums Greenwich.


If you have ever seen a 21st-century marine chronometer, it looks nothing like Harrison’s first designs. To account for unfixable errors in his first three models, Harrison changed his designs in the 1750s to more closely resemble a watch. H4, or Harrison’s first “Sea watch,” was his most accurate creation. Even King George III deemed it a success!

John Harrison was neither the first nor the last to attempt making a chronometer, but he is credited with the most significant breakthroughs in timekeeping and marine navigation in modern history. His designs inspired future inventors and mariners to create increasingly accurate instruments, many of which are still used by navies worldwide. A smart backup if your digital equipment fails!

H4 looks like a large pocket watch with a convex glass cover attached to a silver case. The dial is white enamel with blued steel hour and minute indicators and a silver-colored seconds hand. The hours are indicated by Roman numerals within two black circles, and each five minutes is written in Arabic numerals in the next largest circle. Four identical floral scrolling designs decorate the outside of the dial at the top, bottom, far left, and far right.

An image of H4, Harrison’s breakthrough design that proved more steadfast and accurate over time than any of his earlier inventions. With a diameter of 13.2 centimeters, it is larger than a pocket watch and has its own wooden box case, a setup which chronometer makers still use today. Harrison’s son took it on a voyage to Kingston, Jamaica in 1761. Harrison and his son deemed the voyage a success as the chronometer was only slow by 24/9 seconds per day, but the Board of Longitude thought it was only luck and initially refused to grant the award money. This was one of several battles between Harrison and the Board which went to Parliament and garnered the attention of the King. Harrison eventually won most of the money he felt was owed to him, and future inventors like Larcum Kendall built upon Harrison’s “Sea watch” design to create increasingly accurate timepieces for mariners. Image courtesy of the Royal Museums Greenwich.


A special thank you to Rory McEvoy for his thought-provoking, technical, and understandable explanation of these incredible instruments and the role of the Astronomers Royal!


By Katie Fitzgerald, WPAMC Class of 2019

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