Longitude - Dava Sobel

Question 1

John Harrison

Dates

Answer 1

1693 – 1776)

Question 2

naval disaster of 1707

Answer 2

the Scilly naval disaster of 1707 which took Admiral Sir Cloudesley Shovell and his fleet,

Question 3

the British government established the Board of Longitude in what year?

Answer 3

the British government established the Board of Longitude in 1714.

“The Discovery of the Longitude is of such Consequence to Great Britain for the safety of the Navy and Merchant Ships as well as for the improvement of Trade that for want thereof many Ships have been retarded in their voyages, and many lost…” and announced the Longitude Prize “for such person or persons as shall discover the Longitude.”

Question 4

One degree of longitude equals

Answer 4

One degree of longitude equals four minutes of time

Question 5

In terms of distance, one degree is how many nautical miles or km at the Equator?

Answer 5

In terms of distance, one degree is 60.15 nautical miles or 111 km at the Equator.

Question 6

Size of the Longitude Prize

Answer 6

that the British Parliament offered financial rewards of up to £20,000 (equivalent to £3 or $4-5 million today) under the 1714 Longitude Act.

Question 7

H1

What year did Harrison first come on the scene in London?

Answer 7

In 1730, Harrison designed a marine clock to compete for the Longitude Prize and travelled to London, seeking financial assistance.

Question 8

H1

What did Harrison do with his design when he arrived in London?

Which two notables in London helped Harrison?

Answer 8

He presented his ideas to Edmond Halley, the Astronomer Royal, who in turn referred him to George Graham, the country’s foremost clockmaker. Graham must have been impressed by Harrison’s ideas, for he loaned him money to build a model of his “Sea clock”. As the clock was an attempt to make a seagoing version of his wooden pendulum clocks, which performed exceptionally well, he used wooden wheels, roller pinions and a version of the ‘grasshopper’ escapement. Instead of a pendulum, he used two dumbbell balances, linked together.

Question 8

H1

How long did it take to build?

Answer 8

It took Harrison five years to build his first Sea Clock (or H1).

Question 10

H1

What did Harrison do with his completed H1?

What response did he get?

Answer 10

He demonstrated it to members of the Royal Society who spoke on his behalf to the Board of Longitude. The clock was the first proposal that the Board considered to be worthy of a sea trial.

Question 11

H1 Sea Trial

Date

Journey

How well did it perform?

What was the Board’s response?

Answer 11

In 1736, Harrison sailed to Lisbon on HMS Centurion under the command of Captain George Proctor and returned on HMS Orford after Proctor died at Lisbon on 4 October 1736. The clock lost time on the outward voyage. However, it performed well on the return trip: both the captain and the sailing master of the Orford praised the design. The master noted that his own calculations had placed the ship sixty miles east of its true landfall which had been correctly predicted by Harrison using H1.

This was not the transatlantic voyage demanded by the Board of Longitude, but the Board was impressed enough to grant Harrison £500 for further development. Harrison had moved to London by 1737[8] and went on to develop H2

Question 12

H2

Answer 12

Harrison had moved to London by 1737[8] and went on to develop H2,[9] a more compact and rugged version. In 1741, after three years of building and two of on-land testing, H2 was ready, but by then Britain was at war with Spain in the War of Austrian Succession and the mechanism was deemed too important to risk falling into Spanish hands. In any event, Harrison suddenly abandoned all work on this second machine when he discovered a serious design flaw in the concept of the bar balances. He had not recognized that the period of oscillation of the bar balances could be affected by the yawing action of the ship (when the ship turned such as ‘coming about’ while tacking). It was this that led him to adopt circular balances in the Third Sea Clock (H3).

The Board granted him another £500, and while waiting for the war to end, he proceeded to work on H3.

Question 13

H3

Answer 13

Harrison spent seventeen years working on this third ‘sea clock’, but despite every effort it did not perform exactly as he would have wished. The problem was that, because Harrison did not fully understand the physics behind the springs used to control the balance wheels, the timing of the wheels was not isochronous, a characteristic that affected its accuracy. The engineering world was not to fully understand the properties of springs for such applications for another two centuries.[citation needed] Despite this, it had proved a very valuable experiment as much was learnt from its construction. Certainly in this machine Harrison left the world two enduring legacies – the bimetallic strip and the caged roller bearing.

Question 14

Why is H4 a watch design?

Answer 14

After steadfastly pursuing various methods during thirty years of experimentation, Harrison found to his surprise that some of the watches made by Graham’s successor Thomas Mudge kept time just as accurately as his huge sea clocks[citation needed]. It is possible that Mudge was able to do this after the early 1740s thanks to the availability of the new “Huntsman” or “Crucible” steel produced by Benjamin Huntsman sometime in the early 1740s which enabled harder pinions but more importantly, a tougher and more highly polished cylinder escapement to be produced.[11] Harrison then realized that a mere watch after all could be made accurate enough for the task and was a far more practical proposition for use as a marine timekeeper. He proceeded to redesign the concept of the watch as a timekeeping device, basing his design on sound scientific principles.

Question 15

H4

Answer 15

The “Jefferys” watch Edit
He had already in the early 1750s designed a precision watch for his own personal use, which was made for him by the watchmaker John Jefferys c. 1752–1753. This watch incorporated a novel frictional rest escapement and was not only the first to have a compensation for temperature variations but also contained the first miniature ‘going fusee’ of Harrison’s design which enabled the watch to continue running whilst being wound. These features led to the very successful performance of the “Jefferys” watch, which Harrison incorporated into the design of two new timekeepers which he proposed to build. These were in the form of a large watch and another of a smaller size but of similar pattern. However, only the larger No. 1 (or “H4” as it sometimes called) watch appears ever to have been finished. (See the reference to “H6” below) Aided by some of London’s finest workmen, he proceeded to design and make the world’s first successful marine timekeeper that allowed a navigator to accurately assess his ship’s position in longitude. Importantly, Harrison showed everyone that it could be done by using a watch to calculate longitude.[12] This was to be Harrison’s masterpiece – an instrument of beauty, resembling an oversized pocket watch from the period. It is engraved with Harrison’s signature, marked Number 1 and dated AD 1759.

Question 16

H4 first trial

Answer 16

This first watch took six years to construct, following which the Board of Longitude determined to trial it on a voyage from Portsmouth to Kingston, Jamaica. For this purpose it was placed aboard the 50-gun HMS Deptford, which set sail from Portsmouth on 18 November 1761.[13]:13–14 Harrison, by then 68 years old, sent it on this transatlantic trial in the care of his son, William. The watch was tested before departure by Robertson, Master of the Academy at Portsmouth, who reported that on 6 November 1761 at noon it was 3 seconds slow, having lost 24 seconds in 9 days on mean solar time. The daily rate of the watch was therefore fixed as losing 24/9 seconds per day.[14]

When Deptford reached its destination, after correction for the initial error of 3 seconds and accumulated loss of 3 minutes 36.5 seconds at the daily rate over the 81 days and 5 hours of the voyage,[14] the watch was found to be 5 seconds slow compared to the known longitude of Kingston, corresponding to an error in longitude of 1.25 minutes, or approximately one nautical mile.[15]:56 Harrison returned aboard the 14-gun HMS Merlin, reaching England on 26 March 1762 to report the successful outcome of the experiment.[13] Harrison senior thereupon waited for the £20,000 prize, but the Board were persuaded that the accuracy could have been just luck and demanded another trial. The board were also not convinced that a timekeeper which took six years to construct met the test of practicality required by the Longitude Act. The Harrisons were outraged and demanded their prize, a matter that eventually worked its way to Parliament, which offered £5,000 for the design. The Harrisons refused but were eventually obliged to make another trip to Bridgetown on the island of Barbados to settle the matter.

Question 17

H4 second trial

Answer 17

At the time of this second trial, another method for measuring longitude was ready for testing: the Method of Lunar Distances. The moon moves fast enough, some thirteen degrees a day, to easily measure the movement from day to day. By comparing the angle between the moon and the sun for the day one left for Britain, the “proper position” (how it would appear in Greenwich, England, at that specific time) of the moon could be calculated. By comparing this with the angle of the moon over the horizon, the longitude could be calculated.

During Harrison’s second trial of his ‘Sea watch’ (H4) the Reverend Nevil Maskelyne was asked to accompany HMS Tartar and test the Lunar Distances system. Once again the watch proved extremely accurate, keeping time to within 39 seconds, corresponding to an error in the longitude of Bridgetown of less than 10 miles (16 km).[15]:60 Maskelyne’s measures were also fairly good, at 30 miles (48 km), but required considerable work and calculation in order to use. At a meeting of the Board in 1765 the results were presented, but they again attributed the accuracy of the measurements to luck. Once again the matter reached Parliament, which offered £10,000 in advance and the other half once he turned over the design to other watchmakers to duplicate. In the meantime Harrison’s watch would have to be turned over to the Astronomer Royal for long-term on-land testing.

Unfortunately, Nevil Maskelyne had been appointed Astronomer Royal on his return from Barbados, and was therefore also placed on the Board of Longitude. He returned a report of the watch that was negative, claiming that its “going rate” (the amount of time it gained or lost per day) was due to inaccuracies cancelling themselves out, and refused to allow it to be factored out when measuring longitude. Consequently, this first Marine Watch of Harrison’s failed the needs of the Board despite the fact that it had succeeded in two previous trials.

Question 18

H4 recognition

Answer 18

Harrison began working on his second ‘Sea watch’ (H5) while testing was conducted on the first, which Harrison felt was being held hostage by the Board. After three years he had had enough; Harrison felt “extremely ill used by the gentlemen who I might have expected better treatment from” and decided to enlist the aid of King George III. He obtained an audience with the King, who was extremely annoyed with the Board. King George tested the watch No.2 (H5) himself at the palace and after ten weeks of daily observations between May and July in 1772, found it to be accurate to within one third of one second per day. King George then advised Harrison to petition Parliament for the full prize after threatening to appear in person to dress them down. Finally in 1773, when he was 80 years old, Harrison received a monetary award in the amount of £8,750 from Parliament for his achievements, but he never received the official award (which was never awarded to anyone). He was to survive for just three more years.

Question 19

Money awarded

Answer 19

In total, Harrison received £23,065 for his work on chronometers. He received £4,315 in increments from the Board of Longitude for his work, £10,000 as an interim payment for H4 in 1765 and £8,750 from Parliament in 1773.[16] This gave him a reasonable income for most of his life (equivalent to roughly £45,000 per year in 2007, though all his costs, such as materials and subcontracting work to other horologists, had to come out of this). He became the equivalent of a multi-millionaire (in today’s terms) in the final decade of his life.

Question 20

K1

Answer 20

Captain James Cook used K1, a copy of H4, on his second and third voyages, having used the lunar distance method on his first voyage.[17] K1 was made by Larcum Kendall, who had been apprenticed to John Jefferys. Cook’s log is full of praise for the watch and the charts of the southern Pacific Ocean he made with its use were remarkably accurate. K2 was loaned to Lieutenant William Bligh, commander of HMS Bounty but it was retained by Fletcher Christian following the infamous mutiny. It was not recovered from Pitcairn Island until 1840, and then passed through several hands before reaching the National Maritime Museum in London.

Question 21

Cost of a chronometer

Answer 21

Initially, the cost of these chronometers was quite high (roughly 30% of a ship’s cost). However, over time, the costs dropped to between £25 and £100 (half a year’s to two years’ salary for a skilled worker) in the early 19th century.[18][19] Many historians point to relatively low production volumes over time as evidence that the chronometers were not widely used. However, Landes[18] points out that the chronometers lasted for decades and did not need to be replaced frequently – indeed the number of makers of marine chronometers reduced over time due to the ease in supplying the demand even as the merchant marine expanded.[20][21] Also, many merchant mariners would make do with a deck chronometer at half the price. These were not as accurate as the boxed marine chronometer but were adequate for many. While the Lunar Distances method would complement and rival the marine chronometer initially, the chronometer would overtake it in the 19th century.

Yet the timekeeping device with such accuracy would eventually also allow the determination of longitude accurately, making the device a fundamental key to the modern age. Following Harrison, the marine timekeeper was reinvented yet again by John Arnold who while basing his design on Harrison’s most important principles, at the same time simplified it enough for him to produce equally accurate but far less costly marine chronometers in quantity from around 1783. Nonetheless, for many years even towards the end of the 18th century, chronometers were expensive rarities, as their adoption and use proceeded slowly due to the precision manufacturing necessary and hence high expense. The expiry of Arnold’s patents at the end of the 1790s enabled many other watchmakers including Thomas Earnshaw to produce chronometers in greater quantities at less cost even than those of Arnold. By the early 19th century, navigation at sea without one was considered unwise to unthinkable. Using a chronometer to aid navigation simply saved lives and ships—the insurance industry, self-interest, and common sense did the rest in making the device a universal tool of maritime trade.

Question 22

Subsequent history

Answer 22

After World War I, Harrison’s timepieces were rediscovered at the Royal Greenwich Observatory by retired naval officer Lieutenant Commander Rupert T. Gould.

The timepieces were in a highly decrepit state and Gould spent many years documenting, repairing and restoring them, without compensation for his efforts.[24] Gould was the first to designate the timepieces from H1 to H5, initially calling them No.1 to No.5. Unfortunately, Gould made modifications and repairs that would not pass today’s standards of good museum conservation practice, although most Harrison scholars give Gould credit for having ensured that the historical artifacts survived as working mechanisms to the present time. Gould wrote The Marine Chronometer published in 1923, which covered the history of chronometers from the Middle Ages through to the 1920s, and which included detailed descriptions of Harrison’s work and the subsequent evolution of the chronometer. The book remains the authoritative work on the marine chronometer.

Today the restored H1, H2, H3 and H4 timepieces can be seen on display in the Royal Observatory at Greenwich. H1, H2 and H3 still work: H4 is kept in a stopped state because, unlike the first three, it requires oil for lubrication and so will degrade as it runs. H5 is owned by the Worshipful Company of Clockmakers of London, and was previously on display at the Clockmakers’ Museum in the Guildhall, London, as part of the Company’s collection; since 2015 the collection has been displayed in the Science Museum, London.

Question 23

Final claim

Answer 23

One of the controversial claims of his last years was that of being able to build a land clock more accurate than any competing design. Specifically, he claimed to have designed a clock capable of keeping accurate to within one second over a span of 100 days.[25]:25–41 At the time, such publications as The London Review of English and Foreign Literature ridiculed Harrison for what was considered an outlandish claim. Harrison drew a design but never built such a clock himself, but in 1970 Martin Burgess, a Harrison expert and himself a clockmaker, studied the plans and endeavored to build the timepiece as drawn. He built two versions, dubbed Clock A and Clock B. Clock A became the Gurney Clock which was given to the city of Norwich in 1975, while Clock B lay unfinished in his workshop for decades until it was acquired in 2009 by Donald Saff. The completed Clock B was submitted to the National Maritime Museum in Greenwich for further study. It was found that Clock B could potentially meet Harrison’s original claim, so the clock’s design was carefully checked and adjusted. Finally, over a 100-day period from 6 January to 17 April 2015, Clock B was secured in a transparent case in the Royal Observatory and left to run untouched, apart from regular winding.. Upon completion of the run, the clock was measured to have lost only 5/8 of a second, meaning Harrison’s design was fundamentally sound. If we ignore the fact that this clock uses materials such as invar and peek unavailable to Harrision, had it been built in 1762, the date of Harrison’s testing of his H4, and run continuously since then without correction, it would now (February 2018) be slow by just 9 minutes and 44 seconds. Guinness World Records has declared the Martin Burgess’ Clock B the “most accurate mechanical clock with a pendulum swinging in free air.”

Question 24

TV Adaptation

Answer 24

The book was dramatised for UK television by Charles Sturridge in a Granada Productions film for Channel 4 in 1999, under the title Longitude. It was broadcast in the US later that same year by co-producer A&E.

The production starred Michael Gambon as Harrison and Jeremy Irons as Gould.

Question 25

PBS

Answer 25

Sobel’s book was also the basis for a PBS NOVA episode entitled Lost at Sea: The Search for Longitude.