Longitude by Dava Sobel

(New York: Bloomsbury Publishing USA, 2010), 209

Commonsense Celestial Navigation

Notes


Contents


Introduction

  • Many did have watches, but they might lose or gain five minutes in five hours, requiring resetting several times a day, the accuracy of one's watch being a point of pride. (Location: 31)
  • The experience imparted a vivid memory: Clocks were important. (Location: 36)
  • In this museum, many years ago, I found what I had long hoped to see, perhaps the most significant clocks in history, the first accurate marine chronometers. (Location: 44)
  • The chronometers were also constructed to solve the problem of determining longitude and, to me, they are even more fascinating. (Location: 60)
  • Required by my career field to master aerial and space navigation, I became fascinated with the history of marine navigation. (Location: 62)
  • The early ship captains understood the meaning of latitude and could measure it in the Northern Hemisphere by the elevation of the North Star above the horizon. (Location: 68)
  • none understood longitude. (Location: 69)

Chapter 1: Imaginary Lines

  • The latitude lines, the parallels, really do stay parallel to each other as they girdle the globe from the Equator to the poles in a series of shrinking concentric rings. The meridians of longitude go the other way: They loop from the North Pole to the South and back again in great circles of the same size, so they all converge at the ends of the Earth. (2)
  • A.D. 150, the cartographer and astronomer Ptolemy had plotted them on the twenty-seven maps of his first world atlas. (3)
  • The zero-degree parallel of latitude is fixed by the laws of nature, while the zero-degree meridian of longitude shifts like the sands of time. This difference makes finding latitude child’s play, and turns the determination of longitude, especially at sea, into an adult dilemma—one that stumped the wisest minds of the world for the better part of human history. (4)
  • The measurement of longitude meridians, in comparison, is tempered by time. To learn one’s longitude at sea, one needs to know what time it is aboard ship and also the time at the home port or another place of known longitude—at that very same moment. The two clock times enable the navigator to convert the hour difference into a geographical separation. (4)
  • Every day at sea, when the navigator resets his ship’s clock to local noon when the sun reaches its highest point in the sky, and then consults the home-port clock, every hour’s discrepancy between them translates into another fifteen degrees of longitude. (5)
  • Precise knowledge of the hour in two different places at once—a longitude prerequisite so easily accessible today from any pair of cheap wristwatches—was utterly unattainable up to and including the era of pendulum clocks. (5)
  • In the course of their struggle to find longitude, scientists struck upon other discoveries that changed their view of the universe. These include the first accurate determinations of the weight of the Earth, the distance to the stars, and the speed of light. (7)
  • The British Parliament, in its famed Longitude Act of 1714, set the highest bounty of all, naming a prize equal to a king’s ransom (several million dollars in today’s currency) for a “Practicable and Useful” means of determining longitude. (8)
  • English clockmaker John Harrison, a mechanical genius who pioneered the science of portable precision timekeeping, devoted his life to this quest. He accomplished what Newton had feared was impossible: He invented a clock that would carry the true time from the home port, like an eternal flame, to any remote corner of the world. (8)
  • claimed his rightful monetary reward in 1773— (9)

Chapter 2: The Sea Before Time

  • Longitude Act of 1714, in which Parliament promised a prize of £20,000 (16)

Chapter 3: Adrift in a Clockwork Universe (21)

  • When mariners looked to the heavens for help with navigation, they found a combination compass and clock. (22)
  • The main problem with this “lunar distance method” was that the positions of the stars, on which the whole process depended, were not at all well known. (23)
  • Galileo worked out a longitude solution. Eclipses of the moons of Jupiter, he claimed, occurred one thousand times annually— (25)
  • Galileo’s method for finding longitude at last became generally accepted after 1650—but only on land. Surveyors and cartographers used Galileo’s technique to redraw the world. And it was in the arena of mapmaking that the ability to determine longitude won its first great victory. (27)
  • King Louis XIV of France, confronted with a revised map of his domain based on accurate longitude measurements, reportedly complained that he was losing more territory to his astronomers than to his enemies. (27)
  • Roemer used the departures from predicted eclipse times to measure the speed of light for the first time in 1676. (He slightly underestimated the accepted modern value of 300,000 kilometers per second.) (30)

Chapter 4: Time in a Bottle

  • since time sets its own tempo, like a heartbeat or an ebb tide, timepieces don’t really keep time. They just keep up with it, if they’re able. (34)
  • distinction for completing the first working pendulum clock fell to Galileo’s intellectual heir, Christiaan Huygens, (37)
  • neither Hooke nor Huygens produced a true marine timekeeper. The separate failures of these two giants seemed to dampen the prospects for ever solving the longitude problem with a clock. (39)

Chapter 5: Powder of Sympathy

  • magnetic variation method had one distinct advantage over all the astronomical approaches: It did not depend on knowing the time at two places at once or knowing when a predicted event would occur. (44)

Chapter 6: The Prize

  • This power over purse strings made the Board of Longitude perhaps the world’s first official research-and-development agency. (54)
  • Thacker’s witty neologism is apparently the first coinage of the word chronometer. (57)
  • To prove worthy of the £20,000 prize, a clock had to find longitude within half a degree. This meant that it could not lose or gain more than three seconds in twenty-four hours. Arithmetic makes the point: Half a degree of longitude equals two minutes of time—the maximum allowable mistake over the course of a six-week voyage from England to the Caribbean. An error of only three seconds a day, compounded every day at sea for forty days, adds up to two minutes by journey’s end. (58)

Chapter 7: Cogmaker’s Journal

  • Harrison educated himself (61)
  • young John learned woodworking from his father. (62)
  • John as a teenager let it be known that he craved book learning. (63)
  • manuscript copy of a lecture series on natural philosophy delivered by mathematician Nicholas Saunderson at Cambridge University. (63)
  • He wrote out every word and drew and labeled every diagram, the better to understand the nature of the laws of motion. (63)
  • Although John Harrison forswore Shakespeare, never allowing the Bard’s works in his house, Newton’s Principia and Saunderson’s lectures stood him in good stead for the rest of his life, (64)
  • Harrison completed his first pendulum clock in 1713, before he was twenty years old. (64)
  • It is constructed almost entirely of wood. This is a carpenter’s clock, with oak wheels and boxwood axles connected and impelled by small amounts of brass and steel. Harrison, ever practical and resourceful, took what materials came to hand, and handled them well. The wooden teeth of the wheels never snapped off with normal wear but defied destruction by their design, which let them draw strength from the grain pattern of the mighty oak. (64)

Chapter 8: The Grass hopper Goes to Sea

  • When Graham finally said good night, he waved Harrison back to Barrow with every encouragement, including a generous loan, to be repaid with no great haste and at no interest. (77)
  • H-1 now lives and works (with daily winding) in an armored-glass box at the National Maritime Museum in Greenwich, where it still runs gamely in all its friction-free glory, much to the delight of visitors. (78)
  • the Board of Longitude convened for the very first time—twenty-three years after the board was created—citing his marvelous machine as the occasion. (82)
  • Harrison, now a London resident and forty-eight years old, faded into his workshop and was hardly heard from during the nearly twenty years he devoted to the completion of H-3, (86)

Chapter 9: Hands on Heaven’s Clock

  • The clock of heaven formed John Harrison’s chief competition for the longitude prize; the lunar distance method for finding longitude, based on measuring the motions of the moon, constituted the only reasonable alternative to Harrison’s timekeepers. By a grand confluence, Harrison produced his sea clocks at precisely the same period when scientists finally amassed the theories, instruments, and information needed to make use of the clock of heaven. (89)
  • Perfection of the two methods blazed parallel trails of development down the decades from the 1730s to the 1760s. (89)
  • Hadley’s quadrant boasted its own built-in artificial horizon that proved a lifesaver when the real horizon disappeared in darkness or fog. The quadrant quickly evolved into an even more accurate device, called a sextant, which incorporated a telescope and a wider measuring arc. (91)
  • The moon follows an irregular elliptical orbit around the Earth, so that the moon’s distance from the Earth and relation to the background stars is in constant flux. What’s more, since the moon’s orbital motion varies cyclically over an eighteen-year period, eighteen years’ worth of data constitute the bare minimum groundwork for any meaningful predictions of the moon’s position. (93)
  • astronomers built one of the three pillars supporting the lunar distance method: They established the positions of the stars and studied the motion of the moon. Inventors had put up another pillar by giving sailors the means to measure the critical distances between the moon and the sun or other stars. All that remained for the refinement of the method were the detailed lunar tables that could translate the instrument readings into longitude positions. The creation of these lunar ephemerides turned out to be the hardest part of the problem. (96)
  • lunar parallax, since the tables were formulated for an observer at the center of the Earth, while a ship rides the waves at about sea level, and the sailor on the quarterdeck might stand a good twenty feet higher than that. Such factors required rectifying by the appropriate calculations. (98)
  • The admirals and astronomers on the Board of Longitude openly endorsed the heroic lunar distance method, even in its formative stages, as the logical outgrowth of their own life experience with sea and sky. By the late 1750s the technique finally looked practicable, thanks to the cumulative efforts of the many contributors to this large-scale international enterprise. In comparison, John Harrison offered the world a little ticking thing in a box. Preposterous! (98)
  • Harrison stood alone against the vested navigational interests of the scientific establishment. (99)

Chapter 10: The Diamond Time keeper

  • It took John Harrison nineteen years to build H-3. (101)
  • One of the innovations Harrison introduced in H-3 can still be found today inside thermostats and other temperature-control devices. It is called, rather unpoetically, a bi-metallic strip. Like the gridiron pendulum, only better, the bi-metallic strip compensates immediately and automatically for any changes in temperature that could affect the clock’s going rate. (103)
  • A novel antifriction device that Harrison developed for H-3 also survives to the present day—in the caged ball bearings that smooth the operation of almost every machine with moving parts now in use. (103)
  • Coming at the end of that big brass lineage, H-4 is as surprising as a rabbit pulled out of a hat. Though large for a pocket watch, at five inches in diameter, it is minuscule for a sea clock, and weighs only three pounds. Within its paired silver cases, a genteel white face shows off four fanciful repeats of a fruit-and-foliage motif drawn in black. These patterns ring the dial of Roman numeral hours and Arabic seconds, where three blued-steel hands point unerringly to the correct time. The Watch, as it soon came to be known, embodied the essence of elegance and exactitude. (106)

Chapter 11: Trial by Fire and Water

  • villain—in this case, the Reverend Nevil Maskelyne, (111)
  • The tension between these two men turned the last stretch of the quest for the longitude prize into a pitched battle. (111)
  • Maskelyne took up, then embraced, then came to personify the lunar distance method. (112)
  • Digges made Harrison a new offer: He would buy the first longitude timekeeper that William and his father put up for sale, the moment it became available. (119)
  • H-4 had lost only five seconds—after 81 days at sea! (120)
  • The prize should have gone to John Harrison then and there, for his Watch had done all that the Longitude Act demanded, but events conspired against him and withheld the funds from his deserving hands. (121)
  • 1764, William and his friend Thomas Wyatt boarded H.M.S. Tartar and sailed to Barbados with H-4. (124)

Chapter 12: A Tale of Two Portraits

  • If Harrison expected to receive the full amount of the £20,000 prize, then he would also have to supervise production of not one but two duplicate copies of H-4—as proof that its design and performance could be duplicated. (129)
  • Nevil Maskelyne. The thirty-two-year-old Maskelyne took office as fifth astronomer royal on a Friday. (129)
  • new groundswell in activity directed at institutionalizing the lunar distance method. (130)
  • new longitude act from Parliament. This one—officially called Act 5 George III—put caveats and conditions on the original act of 1714, (130)
  • Over the course of the next six days, Harrison dismantled the Watch piece by piece, explained—under oath—the function of each part, described how the various innovations worked together to keep virtually perfect time, and answered all the questions put to him. (132)
  • Maskelyne produced the first volume of the Nautical Almanac and Astronomical Ephemeris in 1766, (134)
  • The Almanac represents Maskelyne’s enduring contribution to navigation— (135)

Chapter 13: The Second Voyage of Captain James Cook

  • H-5 had proved accurate to within one-third of one second per day. (148)
  • “It would not be doing justice to Mr Harrison and Mr Kendall,” Cook also noted in the log, “if I did not own that we have received very great assistance from this useful and valuable timepiece.” (150)

Chapter 14: The Mass Production of Genius

  • For decades he had stood apart, virtually alone, as the only person in the world seriously pursuing a timekeeper solution to the longitude problem. Then suddenly, in the wake of Harrison’s success with H-4, legions of watchmakers took up the special calling of marine timekeeping. (152)
  • some modern horologists claim that Harrison’s work facilitated England’s mastery over the oceans, and thereby led to the creation of the British Empire—for it was by dint of the chronometer that Britannia ruled the waves. (152)
  • a seaman could buy a good sextant and a set of lunar distance tables for only a fraction of that sum, about £20. With such a glaring cost comparison between the two methods, the marine timekeeper had to provide more than ease of use and greater accuracy. It had to become more affordable. (153)
  • Thomas Earnshaw, who ushered in the age of the truly modern chronometer. (159)
  • Earnshaw who changed the chronometer from a special-order curiosity into an assembly-line item. (159)
  • An escapement lies at the core of any watch or clock; it alternately blocks and releases the movement at a rhythm set by the clock’s regulator. Chronometers, which aspire to perfect timekeeping, are defined by the design of their escapement. (160)
  • Mudge won lasting acclaim for his lever escapement, which appeared in nearly all mechanical wrist- and pocket watches manufactured through the middle of the twentieth century, (160)
  • At the peak of the Arnold-Earnshaw contretemps in the 1780s, prices had come down to about £80 for an Arnold box chronometer and £65 for an Earnshaw. Pocket chronometers could be bought for even less. (162)
  • In comparison tests, chronometers proved themselves an order of magnitude more precise than lunars, primarily because they were simpler to use. The unwieldy lunar method, which demanded a series of astronomical observations, ephemerides consultations, and corrective computations, opened many doors through which error could enter. (162)
  • In 1860, when the Royal Navy counted fewer than two hundred ships on all seven seas, it owned close to eight hundred chronometers. Clearly, this was an idea whose time had come. The infinite practicality of John Harrison’s approach had been demonstrated so thoroughly that its once formidable competition simply disappeared. Having established itself securely on shipboard, the chronometer was soon taken for granted, like any other essential thing, and the whole question of its contentious history, along with the name of its original inventor, dropped from the consciousness of the seamen who used it every day. (164)

Chapter 15: In the Meridian Courtyard

  • Maskelyne’s tables not only made the lunar distance method practicable, they also made the Greenwich meridian the universal reference point. (167)
  • In 1884, at the International Meridian Conference held in Washington, D.C., representatives from twenty-six countries voted to make the common practice official. They declared the Greenwich meridian the prime meridian of the world. (167)
  • He succeeded, against all odds, in using the fourth—temporal—dimension to link points on the three-dimensional globe. He wrested the world’s whereabouts from the stars, and locked the secret in a pocket watch. (176)

Topic: Navigation

Source
-

New Words
-

Created: 2024-12-21-Sat
Updated: 2024-12-26-Thu