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Home , Bimetallic strip, Clockmaker, Grandfather clock, John Harrison, Larcum Kendall, Longitude Act

HOW DO WE KNOW?

HOW TO MEASURE BY ANDREW ROBINSON Before we were able to plot our position at , thousands of sailors lost their lives; the genius of one British -maker changed all that and won the prestigious Longitude Prize in the process

ESPITE THE PATRIOTIC degree of longitude west of Ushant. and practicality of proposed methods, claim in ‘Rule, Britannia!’, the Four ships were smashed and 1,647 which consisted of scientists, naval anthem composed in 1740, sailors drowned; only 26 survived. officers and government officials. Britain was actually far from As a result of the 1707 catastrophe, They included the president of the ‘ruling the waves’ in the mid- the British Parliament passed the Royal Society (Sir ), . As the Royal in 1714. This stipulated the first lord of the Admiralty, the Navy was only too painfully enormous cash prizes for anyone speaker of the House of Commons, aware, neither British sailors – British or otherwise – who could the first commissioner of the Navy nor the seamen of any rival invent a method of measuring and professors of mathematics at D nation, such as France or longitude that would be effective and . Imaginatively, Spain, had a reliable way to determine at sea. The top prize, £20,000, was Parliament also empowered the their position in the open ocean. offered for a method accurate to half committee to offer financial grants This was especially true during foul a degree of longitude. Furthermore, to develop promising proposals. weather, when it was impossible to the act established a Board of observe the positions of the Sun, Moon Longitude to adjudicate the validity and stars. and landfall GREEK GENIUS remained always a precarious affair. The concept of longitude, and of In 1741, a British naval squadron course latitude, dates back to ancient lost its way – along with several ships Greek mathematicians and astronomers and more than half of its crew – off the who accepted that was essentially western tip of South America because a sphere. Earth’s circumference was its estimate of its longitude was some measured with considerable accuracy

Y 200 miles in error. Much closer to by Eratosthenes in the third century M home, in 1707 a British fleet returning BC, but without specifying any from France became lost in fog terrestrial lines of latitude and near the western end of the English longitude. These were invented in the Channel. Its commander, misjudging 2nd Century BC by Hipparchus, who his position as west of the island of also compiled the first known star

AN ART LIBRARY, ALA LIBRARY, AN ART Ushant (at the furthest tip of the catalogue, with about 850 stars

EM Brittany peninsula), sailed north and measured in terms of celestial latitude ran his warships into the rocks of the Hipparchus came up with a framework of lines of and longitude. Hipparchus’s Scilly Isles, which are located a whole latitude and longitude on the celestial sphere framework strongly influenced PHOTO: BRIDG PHOTO:

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HMS Endeavour was captained by ; on a later expedition on the HMS Resolution, a Harrison chronometer helped him navigate

> IN A NUTSHELL

Finding out how to measure longitude was crucial to being able to navigate at sea. Following the launch of the Longitude Prize to Accompanies the 50th anniversary incentivise someone to come up of Horizon and the launch of with a method, one Yorkshire-based Longitude Prize 2014 took up the challenge… www.longitudeprize.org

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Ptolemy, the father figure of between A and B as the crow flies New York, and Honolulu two cartography, in the (the hypotenuse of the triangle). Both behind San Francisco. The 360 century AD. Ptolemy measured his were imprecise, because of uncertainty degrees of longitude are encompassed terrestrial in degrees about the size and shape of the Earth. during the 24 hours of the Earth’s eastwards from a Even assuming the Earth to be a complete rotation, which means that running through the Fortunate Isles perfect sphere, no one knew its exact for every one-degree change in longitude (Canaries), and his latitudes in degrees circumference, or the length of a degree the local time changes by four . north and south of the equator. of latitude or longitude on the ground. Thus the local time on the opposite To determine the longitudes of A possible method for measuring side of the globe (180 degrees different places on his map of the known world, longitude, understood by the ancient in longitude) differs by 4 x 180 = 720 Ptolemy used Pythagoras’s theorem of Greeks, involved the equation of minutes, or 12 hours, as we should right-angled triangles to calculate the longitude with time. As the Earth expect. If navigators were to compare difference in longitude between places rotates on its axis, the time of sunrise their local time, as measured from the A and B. The trouble was that the two gets later the further west you are from celestial clock by detailed astronomical ‘known’ sides of each of Ptolemy’s a given longitude. For this reason, New observations, with the time measured triangles were the distance along a York time is today set five hours behind in at the time of their parallel of latitude between the latitudes time in London, San observations, they would be able to of A and B, and the actual distance Francisco time three hours behind compute their longitude.

THE KEY invented an ingenious device for compensating for the effects DISCOVERY of in a chronometer. It enabled longitude to be deduced from time Harrison’s H-3 timekeeper TEMPERATURE VARIATIONS reduce a mechanical clock’s accuracy through thermal contraction and expansion of its or . John

CTION Harrison produced an initial solution E to this problem in the 1720s, while OLL C making grandfather . His RT

A Wheel balance pendulum comprised rods of steel E

NC and (which di!er in their E F coe"cients of expansion) parallel DE to each other but of di!ering length. They were connected in a Frame containing

TRY OF TRY bimetallic S so-called ‘gridiron’, such that the pendulum remained the same strip that /MINI compensates length no matter its temperature. for temperature Cleverer still was Harrison’s changes MUSEUM invention in his H-3 chronometer

ME (pictured), some time before 1749, of the ‘’ — a device ARITI M nowadays familiar from mechanical central-heating . He riveted together a thin steel strip and a thin brass strip of the same Wheel balance length. When the temperature NWICH/NATIONAL NWICH/NATIONAL increased, the brass expanded EE

GR more than the steel and curved the strip in one direction. When the temperature fell, the brass USEUMS contracted more than the steel and curved the strip in the opposite direction. Two small ‘curb pins’, attached to the free end of the Y X4, ROYAL M ROYAL Y X4,

M bimetallic strip and embracing the outer turn of the balance spring, reduced the spring’s length TOCK, ALA

S slightly with temperature rise, or increased it with temperature John Harrison’s ingenious H-3 fall, compensating for its thermal chronometer, which was the first expansion or contraction. to introduce the bimetallic strip HOTO: THINK HOTO: P

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The method appears very neat but, when it was proposed by astronomer in 1530, it suffered CAST OF Figuring out how to measure position on the from a fatal flaw. At this time, no CHARACTERS planet has taken centuries of scientific endeavour suitable clocks of remotely sufficient accuracy existed. During the 17th Century, the measurement of time (1564- improved with the invention of the 1642), a founder of pendulum-regulated clock by Christiaan modern , Huygens in 1656, followed by his was a pioneer of the patenting of the balance spring refracting telescope. in 1675 – an idea that had earlier In 1610, he squinted occurred to – which through it at ’s was soon incorporated into clocks. But four moons, and sea trials of a built for began to record tables Huygens in the 1660s showed it to be showing the unreliable when a ship swayed, while of their appearance and disappearance Hooke’s balance-spring clock was never around Jupiter. Galileo tested at sea. Moreover, both designs (1629-95), a suggested his tables be suffered from the effects of temperature Dutch physicist, used by navigators as a variation, which caused mathematician and celestial time check to and springs to expand with an increase astronomer with many calculate their longitude. in temperature, and vice versa. achievements, he is perhaps best known for his invention of the JUPITER TIMEPIECE pendulum-regulated A second possible method for clock in 1656. He John Harrison measuring longitude was entirely believed it suitable (1693-1776) was an astronomical, employing careful for determining English carpenter- observation of heavenly bodies. In longitude at sea. turned-clockmaker. Italy, Galileo Galilei, pioneer of the Atlantic trials were Inspired by the prize refracting telescope, made an exciting initially encouraging, money o!ered in the proposal in 1612. For a Galileo but soon it was clear 1714 Longitude Act, had recorded through his telescope that pendulums only he completed his first the movements of Jupiter’s moons and worked properly under , concluded that the moons’ conditions of flat calm. by the planet occurred so frequently now known as H-1, and predictably they could be used in 1735, and his last, anywhere in the world as a celestial H-5, in 1770. Though to calculate time, and hence actively supported longitude. But although Galileo’s idea by the Royal Society, was sound, to apply it was feasible James Cook his work aroused only on land (where it was widely used (1728-79), the great keen opposition from after 1650), not on deck; and it was explorer, made his astronomers. Harrison useless during daytime when Jupiter first Pacific voyage triumphed only in 1773. was invisible, or indeed at night if the in 1768-71, when he sky happened to be overcast. was not permitted to Astronomical measurers of longitude take John Harrison’s were therefore forced to rely on the unique chronometer, (1732-1811), an so-called method of ‘lunar distances’. H-4. He took a copy , was Unlike Jupiter’s moons, Earth’s on his second and convinced that longitude Moon changes position clearly and third voyages, which was best measured at substantially. In theory, this allowed proved invaluable sea by astronomical navigators to compare their locally for navigation and observation, not by measured altitude of the Moon above cartography. It a chronometer. He the horizon, the altitude of a certain supposedly stopped therefore undermined star above the horizon and the angular ticking at almost the Harrison’s marine distance between the Moon and the moment of Cook’s chronometer in the Sun with printed tables. These showed murder in Hawaii. . Using , the same configurations made in Maskelyne launched London or at particular times of the Nautical Almanac in the and night on the same date. 1767, which established Since the navigator knew his Greenwich as the prime local time from the heavens, he meridian of longitude.

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could in principle figure his time difference with London or Paris, Figuring out how to find Longitude enabled and hence his longitude. However, the us to explore and map the planet ‘lunar distance’ calculation was fairly difficult, requiring correction for the effects of refraction, and the dip of the horizon. An imperfection in ’s telescope, a substantial The Longitude Act, passed error in the lunar tables (very likely, by British Parliament under noted Newton), or the inevitable pressure from merchants and mariners, o!ers cash rolling of the ship and the probable prizes for any ‘Person or 1714 lack of training of the observer, would Persons as shall Discover each be enough to make nonsense of a proper Method for the observation. finding the Longitude’.

TIME FOR CHANGE As the 18th Century progressed, 1761-62 however, increasingly good telescopes John Harrison’s became available. At the same time, No. 4 marine chronometer is the accuracy of lunar tables improved trialled on a sea – most notably in the Nautical journey between Almanac, published from the Royal Britain and . Greenwich Observatory from 1767 In two it under the aegis of the Astronomer loses five , Royal, Nevil Maskelyne. Indeed, it was corresponding to an error in longitude of these tables that would eventually earn just two-hundredths Greenwich its position as the prime of a degree. meridian of longitude at an international conference in 1884. Most scientists therefore favoured astronomy, rather than , as the best long- Captain James bet for measuring longitude at sea. Cook takes a copy But in the same period, the accuracy NAVY of Harrison’s No.

US 4 chronometer on of time-keepers dramatically his second voyage improved, too – thanks to the skills of discovery. With of a carpenter-turned-clockmaker occasional astronomical 1772-75 John Harrison. Born in modest corrections, it circumstances in Yorkshire in enables Cook to make 1693, he somehow got to hear of HOTO LIBRARY X2, X2, LIBRARY HOTO remarkably accurate P the Government’s prize for E charts of the Pacific.

NC longitude. His first timepiece, built E

CI in 1715, was a S similar in almost every respect to The prime meridian of others of its day. However, he soon

CTION X2, longitude is established turned to making more original and E in Greenwich at an elaborate mechanisms. In particular, OLL

C international conference, he confronted the problems of

RT as a consequence of

A temperature, by creating a pendulum

E 1884 sailors long calculating whose length remained the same NC their position from E F astronomical tables in regardless of temperature changes. DE the Nautical Almanac, By 1726, he had completed a clock compiled in Greenwich. that varied by no more than a second

TRY OF TRY a over the next 14 . This S brought Harrison to the attention /MINI of the Astronomer Royal, Edmund The Global Positioning System (GPS) begins, with the launch Halley, and Britain’s leading horologist,

MUSEUM George Graham. Graham personally of its first satellite. Four

ME satellites are required to fix the advanced him money, without latitude and longitude of a point 1978 interest or security, to build his No. 1 ARITI on the Earth’s surface with an M chronometer, known as H-1. accuracy of a few millimetres. Completed in 1735, using a balance spring rather than a pendulum, H-1 was sent on a sea trial to Lisbon. On its PHOTO: NATIONAL NATIONAL PHOTO:

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The HMS Beagle, which NEED TO KNOW carried Darwin around the world, had 22 What exactly are longitude and chronometers on board latitude? Find out below

LATITUDE 1 The Earth’s equator is the parallel of zero latitude. The North Pole is at latitude 90° North, the South Pole at latitude 90° South. The parallels encircling the Earth between these extremes, expressed in degrees and minutes, are defined as the angular distance on a meridian north or south of the equator.

LONGITUDE 2 In contrast with latitude, longitude is defined not by Nature but by human choice. The prime meridian, encircling the Earth through the poles, happens to run through Greenwich, having been selected at a conference in 1884. All other meridians define the angular distance east or west of the prime meridian.

TIME ZONES 3 The establishment of (GMT) in 1884 created o"cial international time zones and the international date line through the Pacific Ocean. This lies at 180° of longitude from the prime meridian at Greenwich. return, the chronometer corrected the were not best pleased. The prize money the expectations of its most zealous landfall in Britain by nearly 100 miles. was withheld by the , advocate and by being now and then It gained Harrison the financial support while Harrison and his chronometers corrected by lunar observations has of the Royal Society and the Board of were subjected to increasingly severe been our faithful guide through all Longitude in making four more tests in the 1760s. In 1772, Harrison’s vicissitudes of climates.” By the 1790s, chronometers over the coming decades. son made a personal appeal to King marine chronometers had become H-3, completed in 1757, was never sent George III to test H-5, completed in standard equipment for naval captains. to sea, but it contained Harrison’s most 1770, in his personal observatory at When HMS Beagle left Britain in 1831 important : a ‘bimetallic Richmond. After an embarrassing to survey the world, carrying on board strip’. This allowed for the expansion hiccup in performance, traced to some the young Charles Darwin, it took and contraction of the balance spring nearby royal magnetic lodestones, H-5 along no fewer than 22 chronometers. under changing (see ‘The proved itself accurate to within one-third By then, Britannia really did rule the key discovery’, p94). of a second per day. With the King’s waves – thanks, in part, to its accurate But it was H-4, a pocket-sized watch advice and support, but after further measurement of longitude. „ that weighed ‘less than the brain that resistance from the Board of Longitude, conceived it’ – in the words of Rupert Parliament agreed to pay most of the Gould’s definitive study, The Marine money due to Harrison in 1773. ANDREW ROBINSON is the co-author of Chronometer – that changed . Two years later, not long before The Shape Of The World (Rand McNally) Sent by sea to Jamaica in 1761-62, H-4 its inventor’s death, Harrison’s was found to be just five seconds slow chronometer received an even greater Find out more on arrival, corresponding to an error accolade. Captain James Cook was in longitude of just two-hundredths the greatest explorer of his . On Watch The Clock That Changed of a degree: well within the accuracy his return from his second voyage to The World, in which Adam Hart- specified to win the £20,000 prize. the Pacific, he pronounced that his Davis discusses the device that helped us Naturally, the astronomers – led by chronometer – an exact copy of H-4 measure longitude. youtu.be/T-g27KS0yiY the Astronomer Royal, Maskelyne – made by – “exceeded

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