Most of us are comfortable with pilotage.  This is the practice of navigating from one landmark to the next in a sequence to find your way to your destination.  In fact, most of us have given directions like, “go down Main Street to the third light and turn left, then …” But what do you do when you don’t have ready landmarks, like when crossing the ocean?

Latitude and longitude are artificial grid system we imagine about our planet to help us how we navigate without the use of waypoints or landmarks.  This system of regular circles placed at perpendicular axes give us a precise set of coordinates that describe any location in Earth.  Latitude is set by the equator, a fixed point. That means, even out at sea, it’s simple to gauge your latitude by the length of the day or the position of the sun. But longitude is more difficult.  Because the Earth rotates there is no easy celestial observation that you can sight to help you determine longitude. Every four minutes, longitude shifts one degree. So, determining longitude, especially at sea, was considered an insoluble problem until 1761 when John Harrison developed a clock that was able to keep reliable time for the duration of a typical voyage on a ship that bobbed and swayed with the movement of the sea.

Navigating at sea, far from the sight of land has always been a perilous venture.  Captains generally work by deductive or “dead” reckoning which essentially means taking an educated guess based on an assumed course and calculating where you SHOULD be but never really knowing until you sight land.  Anything that causes the ship to deviate from its planned route (storms, enemy engagements, even doldrums) will result in situations where the ship’s location is simply impossible to determine.

In 1714, merchants and sea captains banded together and brought a petition to the British Parliament to solve the longitude problem. The government offered a hefty reward to anyone who could devise a means of determining, at sea, a ship’s longitude in a reliable fashion.  This Longitude Act, issued on July 8, 1714, offered up £20,000 prize (about £1.5m today) for a practical and useful method to determine longitude to an accuracy of half a degree.

On the face of it, this seems a trivial problem.  After all, like latitude which is measured from the equator, longitude is measured as degrees of rotation from a line that runs through the Royal Observatory, Greenwich England.  To calculate your longitude at sea, all you need to do is compare the time on the ship to the time at Greenwich and the longitude can easily be calculated as one degree for every four minutes difference.  The problem is that while local time can be assessed accurately by the zenith of the sun, the time in Greenwich can only be assessed by having a reference clock set to that time and the only clocks of the day that kept time well enough for these computations required a pendulum which will not work on a ship that is moving, swaying, and bobbing on the sea.

Pocket watches were available and, for the wealthy, quite common but even the best of these lost time due to internal friction within its mechanism.  This is no real issue for someone in the town who can reset their watch to the local clocktower or at noon to the sun’s zenith but when you are distant from the reference (say in India and wanting to reset your watch to Greenwich time) these timepieces are unacceptable for sea navigation.  What was needed was an accurate a reliable chronometer which kept good time even when subjected to harsh movements.

John Harrison was a carpenter by trade who was self-taught in clock making. During the mid-1720s he designed a series of remarkable precision longcase clocks. These clocks achieved an accuracy of one second in a month, far better than any clocks of the time.  To solve the problem of Longitude, Harrison aimed to devise a portable clock which kept time to within three seconds a day. This would make it far more accurate than even the best watches of the time and good enough to allow a reasonable sea voyage without the need to be reset.

Harrison began his time working in London with Edmond Halley, second Astronomer Royal and a Commissioner of Longitude. He was received warmly at Greenwich, but Halley felt unable to judge Harrison’s work. Instead, he sent him to clockmaker George Graham. For the next few years Harrison worked on a marine timekeeper, now known as H1 with the intention of creating something capable of accurately assessing longitude on a transatlantic voyage.

Harrison’s clocks were remarkably innovative. They were virtually frictionless and required no lubrication (due to jeweled bearings), which was unheard of at the time. Without oil, a clock had a much better chance of staying accurate at sea because there were no lubricants to get thicker or thinner as the temperature changed. Because of the clock’s two interconnected swinging balances, it is unaffected by the motion of a ship – it is essentially a portable version of Harrison’s precision wooden clocks.  It seemed that it would be successful in measuring longitude. A trial was called for.

In May 1736, Harrison and H1 were taken aboard HM ship Centurion, which was about to set sail for Lisbon. The aim was to put H1 to the test in a live setting.  The voyage out to Lisbon began poorly for both Harrison and his clock. By the time they reached Lisbon however, the machine was going much more reliably. It was transferred to the Orford for the return, and this journey led to much better results. As they neared England, Harrison announced that a headland the officers had thought was the Start was in fact the Lizard. He was correct. This meant they were 60 miles off course and in danger. It also meant that the H1 was working correctly. 

The results of the Lisbon trial suggested that Harrison might qualify for a reward under the Longitude Act. The Admiralty requested a formal meeting of the Commissioners of Longitude but the establishment scientific community was skeptical.  No one was expecting a break-through from such an unusual challenger. As Dava Sobel writes in her book Longitude: “The only thing more remarkable than the Harrison clocks’ extraordinary accuracy was the fact that such unprecedented precision had been achieved by a couple of country bumpkins working independently.”  When the Admiralty assembled on June 30 1737 to discuss Harrison’s ‘curious instrument’. The Commissioners were not convinced but agreed a payment of £500. £250 was to be paid up front, to allow Harrison to build an improved clock. He promised to do this within two years.

Harrison moved to London soon after the Lisbon trial and within the two years promised he finished his second sea-clock. However, H2 never went to trial, because Harrison had discovered a fundamental flaw. Harrison began work on his third attempt, H3, in 1740, and would continue to work on it for 19 years. While it was running and being tested within five years, it became clear that the clock would struggle to keep time to the accuracy desired. Harrison was forced to make many changes and adjustments.  Evenutally, in 1752 Harrison as ready to show the Admiralty his improved H4 chronometer and he had commissioned John Jefferys to make in the form of a pocketwatch with a radically new type of balance.

No one in the 1750s thought of the pocket watch as a serious precision timekeeper. While H4 initially looked like a large pocket watch, the instrument was in fact quite different.

The secret can be heard in its rapid ticking. H4 ticks five times a second, since its large balance beats more quickly and with larger oscillations than a typical watch.  In 1761 the Commissioners gave permission for Harrison’s son, William, to prepare for a voyage to Jamaica to trial the H4 timekeeper. The trial seemed to go well. On the way out, William used it to predict an earlier landfall at Madeira than the crew were expecting. This impressed the captain so much that he asked to buy their next timekeeper.   

But in England, the Commissioners decided that the test had not been sufficient and the prize would not be awarded.  Harrison’s friends and supporters began a propaganda campaign of newspaper articles, broadsheets and pamphlets.  Harrison was never awarded the full £20,000 prize but his work set the stage for British domination of the seas well into the 20^th Century.  Navigation using an accurate chronometer is still de rigor today with our complex constellations of GPS satellites, all computing position based on time.

---

Want to have the
Regimental Brewmeister
at your site or event?

You can hire me.

https://colonialbrewer.com/yes-you-can-hire-me-for-your-event-or-site/