This post is part of a series, Reading Time at HSNY, written by our librarian, Miranda Marraccini.

At the Horological Society of New York’s (HSNY) Jost Bürgi Research Library, we have at least 15 books from the 18th century – an era of explosive growth and lightspeed technical innovation for horology. Some of our most well-known horological manuals date to this period.

One of the jewels of our collection is a first edition of Ferdinand Berthoud’s 1763 work Essai sur L'horlogerie (You can view a copy held by the Getty Museum here). Berthoud, an important horologist in Paris, developed his own version of the marine chronometer, a game-changing device that eventually enabled people to determine longitude at sea. Although Berthoud’s invention is not the one credited as the first, it is one part of a fascinating story.

Before the mid-18th century, marine navigation was a serious problem. Mariners could determine their latitude by looking at the angle of the sun during the day or the North Star at night, but they couldn’t measure longitude in the same way. It was, for centuries, an unsolvable puzzle, but navigators did the best they could by using dead reckoning, basically a form of guessing based on an estimate of speed. They also used complicated navigational tables and celestial charts to try to work out longitude.

The mathematical method took an enormous amount of calculation. In The Mariner’s Compass Rectified (1750), Andrew Wakely writes in his preface about compiling the data for the book: “my Labour was so great, that I almost fainted.” This book, which we have in our collection at HSNY, was written by two mathematicians and published by a printer in London “where you may have all Sorts of Sea-Books,” showing that math and horology were intrinsically tied to navigation. Below, two somewhat crude illustrations from The Mariner’s Compass nonetheless demonstrate effectively how to use two basic navigational instruments, the fore-staff (image 3) and the quadrant (image 4).

During the course of the century, there was constant debate about how to improve navigation. Some mariners maintained that they needed to be able to tell time at sea so that they could calculate how far they had traveled from their starting point – for British sailors, that would be Greenwich, as in Greenwich Mean Time. But many still believed navigation should be improved by advances in astronomical calculation, rather than the invention of new timekeeping devices.

Long pendulum clocks, which were the most precise means of keeping time on land, wouldn’t work on a ship that was in constant motion. And although spring-driven clocks had been invented in the late 17th century, they too could be affected by a ship’s movement, as well as factors like temperature (which can cause metal to expand and contract), pressure, and corrosion. So horologists had to come up with something new. The British government even established a Board of Longitude to administer a prize worth up to £20,000 (equivalent to millions in today’s money) for a workable idea.

A number of people tried to solve the problem in novel ways. One theoretical solution was published in the Gentleman's Magazine in 1737, an issue that we have in our library (image 5). The article about the “important secret of the longitude” is signed only “The Farmer.”

“The Farmer” describes a new clock called the Perpetual Motion that he developed based on the previous work of his “most ingenious” friend, the horologist Joseph Williamson. The author claims it is so precise it will only gain or lose four seconds in a month.

Though it’s essentially still a pendulum clock, with some improvements, the author claims that if the clock is hung on a ship so that it remains perpendicular at all times, “the motion of the sea will not affect it.” A heavy weight attached to the bottom of the case will “master all Shocks.” This seems doubtful, but the author, citing no less of an authority than Sir Isaac Newton, points out that because of the Earth’s revolutions, “our Clocks on Shore are turned Topsy-turvy every 12 hours,” and they still keep time! He seems to recognize that his case isn’t entirely convincing, and recommends that ships carry “a good Spring-Clock” and “good Watches” as backup, to be reset daily according to the “Perpetual Motion.”

At the end of the article, the editor responds with an acknowledgment of the proposal’s flaws, and an invitation: “And now I ask, whether a better can be framed, and challenge the whole World to produce it.” The horologists of the world, particularly Ferdinand Berthoud, British carpenter John Harrison, and French clockmaker Pierre LeRoy, were working on it.

By the later 18th century, the science of celestial navigation had progressed somewhat, and mariners were starting to use the lunar distance method for figuring out longitude. This series of celestial calculations was first theorized more than 200 years earlier, but not published and popularized until 1763. One of our books, Epitome of the Whole Art of Navigation (1782), promises to teach the lunar method, as well as everything you would need to become a “complete NAVIGATOR,” including lots of logarithmic tables. The primary author is James Atkinson, who also co-wrote the Mariner’s Compass earlier in his career.

Image six shows one of several fold-out maps and charts in this book, along with a diagram of longitude and latitude at left.

Someone named Samuel Carrington owned this copy, and signed it very neatly in 1784, just a couple of years after it was printed (image 7). It’s a common name, but I did find one record of a London shopkeeper, Samuel Carrington, who testified as a witness to an attempted murder in 1828. It may be our book’s first owner!

The lunar distance procedure described in Epitome of the Whole Art of Navigation caught on quickly. We have another book published around the same time in Utrecht, in French, that discusses the same method. Mariners continued to use it even after the chronometer was invented, because it was cheap and accurate enough for shorter journeys.

Finally, John Harrison developed several working prototypes of the marine chronometer, culminating in the H4 in 1761, which served as the basis for improvements by LeRoy and Berthoud, among others. While building his earlier models, H1 through H3, Harrison developed a series of complicated inventions meant to compensate for movement and changes in temperature at sea. In H4, he finally abandoned these, developing a small spring-driven movement with a balance wheel that could oscillate at a higher frequency than the balance wheel in a normal watch, which made it much more usable on a ship. The images below show postcards in our collection from the Royal Observatory and the National Maritime Museum, both in Greenwich, England. They depict John Harrison (image 8) along with his four prototype marine chronometers, H1, H2, H3, and H4 (image 9).

As further improvements made marine chronometers more precise, reliable, and affordable, adoption surged. By 1820, enough people had tried out the new chronometers for George Fisher to publish Errors of Longitude, a book in our collection which includes tables laying out how far different expeditions had deviated from their intended course. Fisher calls chronometers “almost indispensable articles” in the “present improved state of navigation,” but seeks to improve their function for the future through detailed observation. And indeed marine chronometers continued to serve their indispensable purpose until the 1960s, when they began to be replaced by electronic systems and eventually GPS. Here at HSNY, we have an American marine chronometer made by Elgin from the 1940s in our permanent collection. For more about marine navigation, library visitors can peruse our modern books on the subject, including Dava Sobel’s Longitude: the True Story of a Lone Genius who Solved the Greatest Scientific Problem of His Time and even kids’ books like The Discovery of Longitude by Joan Marie Galat and The Longitude Prize by Joan Dash.

It would be difficult to overstate the importance of the marine chronometer. It completely changed the course of navigational history, and history in general. Because it allowed mariners to navigate accurately over long distances, it contributed to the dominance of the British Royal Navy and all of the consequences of colonization. This complicated legacy plays out over the history of modern horology, driving the perpetual motion forward, over the horizon, tick by tick.