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John Harrison and the Solution to the Longitude Problem

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To grandmother’s house I go—eventually. I’m not sure how this happened, but once again, I’m lost. I’m quite certain that I’m going the wrong way. I don’t doubt that I’m not where I’m supposed to be, but I have no idea where I am.

I’m not surprised. In fact, I’ve planned to be lost—I always do on road trips. I’ve been lost on the road, lost in translation, and lost in my thoughts, but I’ve never been lost at sea.

In the interest of full disclosure, I should mention that I’ve never been to sea, but that is entirely beside the point. I’ve also never been an early 18th century mariner, and that is very much nearer to the point. The point is longitude.

Longitude is, of course, the complement to latitude and is used to measure an object’s distance east or west of the prime meridian, which is currently placed at Greenwich, England.

Although the prime meridian is the zero point for longitude, its position—unlike that of the equator, the equivalent point for latitude—is completely arbitrary. Feel free to choose your own for private use—just don’t become a cartographer. Seriously, that would be monumentally impolite.

Impolite as it may be, various people, Ptolemy arguably the most famous, have taken it upon themselves to select a prime meridian for the rest of us (Ptolemy’s was in the Canary islands).

For most of human history, it was impossible to accurately measure longitude at sea. The “longitude problem,” as it came to be known, was a complicated one. So complicated, in fact, that King George I of Britain formed a Board of Longitude composed of A-List scientists, sailors, and other notables to issue a £20,000 prize to anyone who could find a way to measure longitude within half a degree of a great circle. Half a degree of longitude is equivalent to 34 miles of lateral distance at the equator.

As of this writing, £20,000 in 1714 is equivalent to about $1,000,000 (I’m not an economist; any economists out there who take issue with my estimate are free to leave angry comments). The board also offered second and third place prizes for slightly less accurate solutions.

The solution to the “longitude problem” depended upon knowing local time on a ship in relation to a home port. One hour of time difference is equivalent to 15 degrees longitude, so the center of the central time zone, which is six hours behind Greenwich Mean Time, is separated from Greenwich by 80 degrees of longitude.

Serious contenders for the prize were divided into two camps: astronomers and clockmakers.

Some of the great minds of the age advocated astronomical solutions. Galileo spent several years observing the moons of Jupiter. He asserted that eclipses of the moons of Jupiter occurred regularly enough to allow sailors to mark time by them, allowing sailors to ascertain their position. Unfortunately, the moons of Jupiter are difficult to see during the day and sometimes at night as well.

Other astronomers were fans of the lunar distance method, which used the distance between the moon and the stars to measure longitude. Initially, astronomers lacked the data to measure such distances. Royal Astronomers, including Neville Maskelyne, a staunch opponent of the mechanical method, soon remedied this. But even with the immeasurably helpful almanacs and data the royal astronomers had so dutifully collected, the mathematics involved and the precise observations required of sailors made the lunar distance method cumbersome.

The clockmakers began their work in earnest with a 1660 shipboard test of a pendulum clock built by Christian Huygens. Unfortunately, the pitching of the ship wreaked havoc on the mechanism. Temperature, pressure, and humidity variations were disastrous for clocks aboard ships.

Even if, by some miracle, all of those variables were held constant, winding and lubrication still posed problems. For many years, watches had a tendency to stop, slow down, or run backwards when wound. Obviously, such behavior would seriously limit the accuracy of a timepiece, but watches had to be wound—in an age before batteries, there was little alternative. Also, for many years, friction, the same force which automobile brakes apply to the wheels of speeding cars, threatened to slow down or even stop the gears inside a clock.

To avoid friction, clockmakers turned to lubrication. The lubricants they used, however, tended to change viscosity or thickness. This could slow or even destroy a clock.

With so much prize money at stake, the board received any number of other solutions to the “longitude problem,” from the impractical (fleets of ships at fixed positions across the ocean firing cannons) to sadistic (wounding a dog and applying at a fixed time in the home port a powder that could instantly heal his wound).

The “longitude problem” was finally solved by a man named John Harrison. Harrison was born in 1693 in Barrow, Lincolnshire, England, the son of a carpenter who taught him woodworking. As far as we know, John Harrison had no formal education. He built his first clock in 1713, making the moving parts out of a special wood that secreted natural grease and required no lubrication.

In 1737 he built his first marine clock. Over the next 33 years he built four more, each better than the one before. The first weighed 75 pounds. The last could be carried comfortably in a pocket.

Harrison’s clocks sported a revolutionary friction-free mechanism and a variety of metals that complemented each other so that as one part expanded with the temperature, its mate contracted. As for winding, required every thirty hours or so, the operation of Harrison’s watches was largely unaffected by it. His final watch lost less than half a second a day, even aboard ship.

Along the way, Harrison’s notes were confiscated, his secrets revealed, and his creations tested by his archnemesis, the Royal Astronomer, Neville Maskelyne. In 1764, Harrison was also required to surrender to the Board all of his marine clocks and then to build, from memory, two replicas of H-4, the fourth of his sea clocks. Only these two replicas would suffice to prove to the board that Harrison’s method was “practicable and useful” as the bill demanded.

The events of the spring of 1765 were to prove pivotal in Harrison’s quest for the longitude prize. At that time Parliament passed a new law that added more requirements for winning the prize. Harrison is named explicitly in the bill.

The first of the replicas the board required, Harrison’s final watch, was completed in 1770 and named H-5. Harrison was 77.

By this time, Harrison had made at least one powerful friend—King George III. King George personally tested H-5 at his personal observatory at Richmond in the summer of 1772. The watch performed splendidly, after some initial problems which were solved when a magnet that had been left in the testing room was removed.

In 1773, the Board of Longitude discussed the Harrison case for the last time. Two members of Parliament were present this time, and after a passionate appeal form Harrison, they granted him a bounty through the benevolence of Parliament. The Board declined to award Harrison the actual prize.

In fact, the conditions for winning the prize were changed in 1773 to include a stipulation that two of any timekeeper vying for the prize be submitted.

John Harrison died in 1776. The longitude prize was never claimed. The Board of Longitude was dissolved in 1828.

For a more thorough treatment of “the longitude problem” I recommend Dava Sobel’s Longitude, an excellent book that proved very useful in the preparation of this article.

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About Brian Burns

  • duane

    I think I get it, but you didn’t mention how the local time was measured. Sun and Moon? Does the measurement of local time also depend on latitude? If so, how was that measured? Polaris? What about daylight measurements of latitude?

    Nice writeup.

  • Brian Burns

    Duane,

    Local time was measured sing a sextant, and is I think, latitude independent.