Oct 18 Harrison's Clocks

John Harrison was a joiner and clockmaker born in 1693. Along with his brother he joined the family business of making clocks and watches, both on the large scale for church towers and on a smaller scale for homes and pubs with long case specimens. He would go down as one of the most famous clockmakers in history (although, even I, with my vague interest in horology, could only name two other clockmakers and one of them is myself).

Most of his early clocks were built to the usual specifications of the day with no improvements, but in 1720 he started adding in his own innovations. In a clock there is always something moving with a constant time period such as a pendulum. There needs to be something which counts how many times the period has happened and provide that data as slowly spinning the cogs, which we call an escapement. Up until that point in history we had mostly used something called an anchor escapement which looked like this:

Anchor Escapement

However Harrison invented the grasshopper escapement which had low enough friction that you could make most of it from wood and still not need lubrication:

Grasshopper Escapement

But the main focus of this article will be on the Longitude Problem. In the early 1700s trade between nations was booming with transatlantic voyages becoming commonplace. However working out your longitude wasn't easy and so ships frequently misjudged how far West or East they were. Every day on a voyage the calculations for trajectory were made based on the supposed position from the previous day which meant that errors compounded in a process known as dead reckoning. The number of shipwrecks during this period of history was huge and various European Governments decided to step in with financial rewards for a solution. The British Government passed the Longitude Act in 1714 which offered up to £20,000 for a sufficiently accurate method which would have been around £2.6 million in today's money.

Two main methods were competing for the prize: the first was called The Method of Lunar Distances, which worked by noting that the Moon moves about 13 degrees across the sky every day, which is enough that it can be measured and used for some (complicated) triangulation. The other method which was favoured by Harrison was to build a good enough clock so that accurate time could be kept on the voyage. If the time was known then they could consult their celestial maps and base their location on where the stars were. However the changing humidity and temperature, the rocking of the boat and the salty (read corrosive to metal) air meant that all of the clocks built before that point were just too inaccurate for the purpose. Newton (champion of the Lunar Distances Method) observed that "a good watch may serve to keep a reckoning at sea for some days and to know the time of a celestial observation; and for this end a good Jewel* may suffice till a better sort of watch can be found out. But when longitude at sea is lost, it cannot be found again by any watch."

*Jewels were used at the ends of the axels of the faster moving gears and Diamonds, Rubies and Sapphires were common before the 20th century. Now days Jeweled watches are usually glass.

Harrison sought funding to undergo the project and after visiting Edmond Halley (of comet fame) the Astronomer Royal in 1730 he was given the name of George Graham, one of the foremost clockmakers of the time. Graham was impressed with Harrison's ideas and funded the first project which we now refer to as H1 (Harrison 1). While it was massive, the clock (usually called a chronometer when on a ship) had several important innovations. As well as using Harrison's grasshopper escapement it also used alternating iron and brass rods which alternately expanded and contracted as they warmed up, essentially cancelling out the thermal expansion. However H1 was mostly just the same idea as a Harrison land clock, albeit made to a high specification. By 1735 this first prototype was ready to be tested and in 1736 Harrison secured himself a place on a ship on a trip to Lisbon and back. While it lost time on the way there on the journey back it proved itself more accurate than the captain's own calculations based on landmarks.

H1

This didn't meet the Royal Society's requirements for a demonstration of longitude because it wasn't yet transatlantic. However he was awarded £500 to continue improving on his designs and he started constructing a smaller H2. The construction and on land testing took until 1741, but a war with the Spanish (the War of Austria Succession) delayed any testing on actual ships for fears that the Spanish would get their hands on it. This was unfortunate because H2 had a fatal design flaw which was that the yawing (see below) of the boat caused the clock to lose or gain time.

The three directions that a boat can turn. Yaw is side to side motion.

H2, the one that didn't work.

Harrison abandoned the second clock and started again with H3, which ended up looking quite similar. It took an incredible 17 years of work and was complete around 1750. However, the physics of springs wasn't understood completely at that point in history and this proved to provide sources of error that Harrison couldn't control. Harrison realised that the huge, slow moving balances (the bit that has a constant time period, like the pendulum in a grandfather clock) he had been using where just not accurate enough. Instead he sought to make fast moving, small balances in pocket watch scaled pieces.

H3

Time marched on and Harrison was 68 by the time his first Sea Watch, H4, was ready for testing. In 1761 H4 was sent aboard the HMS Deptford to Jamaica where it only lost 5 seconds over its 81 day journey, corresponding to a longitude error of only about one nautical mile. This was a huge success and when Harrison's son returned to Britain to report to his father, who had been too old to travel, Harrison Snr was elated. He applied to the Royal Society for his £20,000, but they responded that it could have been a fluke and they demanded a second test. Harrison tried suing them and it went to the House of Commons who settled on offering £5000 for the design which the Harrisons refused.

H4, Face and Movement.

Eventually a second voyage was agreed upon to settle the matter and H4 was sent aboard the HMS Tartar to Barbados. On the same ship was one of Harrison's rivals Reverend Nevil Maskelyne who was testing The Method of Lunar Distances which was the alternative way of claiming the longitude prize and which had recently had some breakthroughs. Both methods proved very strong, with Harrison's H4, once again in the hands of John Harrison Jnr, only losing 39 seconds over the trip which corresponded to about 10 miles of inaccuracy in longitude. Maskelyne's calculations were also accurate and corresponded to about 30 miles of error, but were far more complicated to work out.

On their return the British Government were impressed and they initially offered a £10,000 advance to Harrison and the rest of the prize once the watches had been successfully copied by other watchmakers for mass production. However it was up to the Astronomy branch of the Royal Society to decide and upon his return from the West Indies the new appointee for Astronomer Royal was none other than Nevil Maskelyne. He claimed that the watch had managed to cancel out its errors one way with errors another and had lucked out again.

The board kept H4 for testing and Harrison was not permitted use of it. While he worked on an upgraded sea watch H5 the Royal Society were using his design and he had not been awarded the prize. He was furious at their actions and sought to appeal against parliament by enlisting the help of the Monarch, King George III. While George III may be better known for other things like losing the American colony or going mad, he was a big investor of the sciences. Harrison was granted an audience which ended in the King taking H5 away with him to test. After a month he declared it had only lost a third of a second a day which impressed him enough to become an ally of Harrison. He wrote a letter to Parliament threatening to appear in person if they didn't award the prize, to which they slightly relented and gave him £8,750 in 1773 which brought the total amount he had collected from them to £23,065 from over the years. However they didn't actually give Harrison the award which he had spent his whole life seeking.

H5

Versions of the H4 and H5 were made and sold to ships around the world, essentially solving the longitude problem. They were very expensive for the first decade and a half, with the cost of the chronometer representing about 30% of the cost of the ship.

John Harrison died in 1776 having lived the end of his life in extreme wealth. The full Longitude Award was never officially given to anyone, but he had spent his life collecting smaller sums. All of these clocks are at the Greenwich Observatory (which is the most Myst like place in the world), but without this story they are just some old clocks that you will spend two seconds looking at: it is by knowing a history of an object that gives something interest. These three clocks and two watches represent the entire lifetime of a man obsessively trying to solve a single problem and that strikes me as a life well spent.

John Harrison