Rating: 
Summary: The Man who Captured Time so Ships could Navigate Accurately
Review: +++++
Note: This review has been written from a city with the following position on Earth:
LATITUDE: (43 degrees 2 minutes North)
LONGITUDE: (81 degrees 9 minutes West)
In order to understand the significance of this remarkable book by Dava Sobel, the reader has to understand some words and phrases in the book's title and subtitle.
"Longitude" along with Latitude are two numbers along with compass directions that are used to fix the position of anything on the planet Earth (as in the note above). Lines of Latitude are the imaginary, parallel, horizontal lines circling the Earth with the equator (fixed by nature) being the "zero-degree parallel of latitude." Lines of Longitude or "meridians" are the imaginary lines that run top to bottom (north and south), from the Earth's North Pole to its South Pole with the "prime meridian" (established by political means) being the "zero-degree meridian of longitude." (Since the mid-1880s, the prime merdian has passed through Greenwich, England. Before this time, the imaginary line that passed through a ship's home port was usually used as the zero-degree meridian.)
Finding the latitude on land or at sea was easy and eventually a device was invented to make it even easier. But finding longitude, especially at sea on a swaying ship was difficult, a difficulty "that stumped the wisest minds of the world for the better part of human history" and was "the greatest scientific problem" of the 1700s. Ways of determining longitude astronomically were devised, but these proved to be impractical when used at sea.
England's parliament recognized that "the longitude problem" had to be solved practically since many people and valuable cargo were lost at sea when the ship's navigators lost sight of land. Thus, this parliament offered a top monetary prize that's equivalent to many millions of dollars today to anybody who could solve the problem.
Enter "a lone genius" named John Harrison (1693 to 1776). While most thought the solution to the problem was astronomical, Harrison saw time as the solution.
To calculate the longitude using time on a ship at sea, you have to realize these two facts found in this book:
(i) The Earth takes 24 hours of time to spin 360 degrees on its axis from east to west.
(ii) Noon (12:00 PM) is the highest point the sun seems to "travel" in a day.
To learn one's longitude at sea using time, as this book explains, it's necessary to do the following:
(1) Know the time it is aboard ship (local noon was normally used because of fact (ii) above).
(2) At the very same moment, know the time at a known longitude (such as at Greenwich, England).
(3) The difference in time between (1) and (2) is coverted to a longitude reading in degrees and direction (using fact (i) above).
Harrison's solution was the accurate determination of time of (2) above by inventing a reliable timepiece. This timepiece, in this case, would be set to Greenwich time. (Note that, as stated, (1) could be determined using the noon-day sun but this was not always practical. Eventually another timepiece was used to determine the ship's local noon for a particular day.) It has to be realized that this was the "era of pendulum clocks" where, on a deck of a rocking ship, "such clocks would slow down or speed up, or stop running altogether." Harrison was to capture time by building a marine clock or "timekeeper" (eventually called a "chronometer") that could be used on a ship at sea.
This book tells the "true story" of Harrison and his chronometers. (There were five built over a forty-year period. Harrison's first timekeeping device was known as H-1, his second was H-2, and so on.) Sobel uses accuracy (as evidenced by her thirty references), extensive interviews, and an engaging, mostly non-technical narrative (only essential technical detail is included) to convey a story that's filled with suspense, heroism, perfectionism, and villiany. All this in less than 200 pages!!
The only problem I had with this book is that it has hardly any pictures (photographs and illustrations). I would have liked to have seen pictures of the various people involved in this saga, maps showing where ships traveled, more photos of Harrison's amazing timepieces (both interior and exterior), and diagrams that explained important concepts. A diagram that actually showed how longitude, using a simple example, is calculated (using the steps above) would also have been helpful.
Finally, there is a good 1999 movie entitled "Longitude" based on this book. Be aware that even though this book is short, the movie is long (over three hours).
In conclusion, this book documents the exciting "true story" of how "a lone genius" solved "the longitude problem." Sobel states this more eloquently: "With his marine clocks, John Harrison tested the waters of space-time. He succeeded, against all odds, in using the fourth...dimension to link points on a three-dimensional globe. He [took] the world's whereabouts from the stars, and locked [or captured] the secret in a...watch."
+++++
Rating: 
Summary: take it with you around the world
Review: A wonderful short account of how a great obstacle was overcome. Before Global Positioning System satellites, the only way to know where you were on a parallel of latitude (the equator, say, or the Tropic of Capricorn) was to "shoot the sun" at noon and compare the reading with that at a fixed point (Greenwich, say). Ah, but there's the rub! The comparison is useless unless you know what time it is. So navigation depended on creating a timepiece that for all practical purposes would keep accurate time for the months and even years of a sailing voyage. How that timepiece was developed is the story in this book. If you plan to sail around the world, you should own a copy and keep it right beside your GPS receiver!
Rating:
Summary: Tremendous tale of the era's ultimate scientific challenge
Review: As exploration of the Earth reached its zenith, the most daunting problem for navigators was the inability to determine longitude - exact "horizontal" location on the globe, in navigational terms. After a devastating shipwreck off the coast of England - which resulted in thousands of lives lost - Parliament offered a stunning prize of 20,000 pounds sterling (the equivalent of perhaps $20 million today) to any person who could solve "the longitude problem".Over six decades, John Harrison - an exceedingly clever "horologist" (timepiece builder) - defied the conventional scientific wisdom of an astrological solution to the problem. Building a chronometer suitable for both wide temperature ranges and the continual pitch and yaw of maritime travel proved exceedingly difficult. Yet Harrison's creative attempts were stunningly accurate and unbelievably durable. How he built these complex devices - and handled the politically incorrect nature of his approach - is the story of Longitude. This is a wonderful, fast-moving read which covers a topic of surprising import.
Rating:
Summary: A little Gem!
Review: Beutiful writing, surprising history all done with brevity and accuracy. How sailors were able to find their way at sea, and what would happen when they didn't. How ego blocked recognition of the genius who did it. Here is a wonderful little book for your next 3-4 hour airplane travel. We can anticipate more fine writing by Dava Sobel.
Rating:
Summary: Fascinating Subject
Review: Dava Sobel has written a beautiful book about a subject that in a lesser author's hands could have been exceedingly boring. The need for a clock which would accurately keep time while on a sea voyage in order to help mariners determine their longitude and thus accurately determine where they would land doesn't seem like it would be that exciting. However, Sobel has given a wonderful account of the problems that were encountered without this device and how John Harrison, a clock maker, was determine to solve this problem with an accurate time piece that could be used even on ships. The tremendous difficulties that Harrison had in convincing the British government authorities that he had indeed solved the problem are interesting and yet his endurance in solving this problem is almost heroic. Apparently, red tape and professional jealously are timeless qualities of human nature. This slim book provides an interesting glance into a subject which probably few have ever thought about. I would recommend this book highly to anyone who likes to know the story behind scientific discoveries which now seem almost quaint
Rating:
Summary: Nice Lean Account of Quest to Calculate Longitude at Sea.
Review: For centuries, the inability to calculate longitude at sea doomed many a sailing vessel and its cargo. Unable to calculate their exact position, ships would run aground or miss their destinations entirely, leaving their crews to suffer and sometimes parish from starvation, scurvy, or infectious disease. By the 18th century, the lives and monies lost as a result of this inability to navigate properly had become such an obstacle to commerce and political ambitions that, in 1714, England's Parliament offered an extraordinary sum of money to anyone who could devise a method of reliably calculating longitude at sea. Dava Sobel's "Longitude" is the story of the approximately 60-year race to solve the longitude problem and its hero, a clockmaker from Yorkshire named John Harrison, who invented what we now call the chronometer. Ms. Sobel has written a short, very readable account of the technologies, personalities, and politics surrounding the quest for a solution to the longitude problem and its accompanying prize. The book owes its economy -only 180 pages- to the fact that the author doesn't attempt to place the longitude problem in a greater historical context or to say more than is necessary about the individuals who play a part in the story. "Longitude" concentrates on one story, which is the book's strength as well as a limitation. If the story intrigues you, there is more to be learned elsewhere about navigation at sea, the technology of the chronometer, John Harrison, and all the other grand personalities that inhabit this tale of discovery and the politics of science. But "Longitude" is a brisk, enjoyable account of the invention that solved a centuries-old problem and propelled Great Britain to global dominance.
Rating:
Summary: Longitude
Review: I found this book to be a great read and quite informative. The topic is not something that I usually concern myself with, but when I came across the book awhile back, I figured that someday I should read it; that day came, and I'm quite glad I did. It's made me aware of a man I was heretofore not familiar with--John Harrison--and the significance of his inventions. What he accomplished was truly revolutionary, and his story deserves to be known; this highly readable account apptly serves that purpose.
Rating:
Summary: John Harrison--an extraordinary person
Review: John Harrison (1693-1776) spent his lifetime inventing and perfecting a series of timepieces to measure longitude. As Dava Sobel relates in her engaging narrative, "Longitude," until the 18th century sailors navigated by following parallels of latitude and roughly estimating distance traveled east or west. Ships routinely missed their destinations, often taking excessive time to arrive or succumbing to reefs off fogbound shores. Thousands of sailors and tons of cargo were lost. In 1714, England's Parliament offered £20,000 (the equivalent of about $12 million today) to anyone who provided a "practicable and useful" means of determining longitude. Countless solutions were suggested, some bizarre, some impractical, some workable only on land and others far too complex. Most astronomers believed the answer lay in the sky, but Harrison, a clockmaker, imagined a mechanical solution--a clock that would keep precise time at sea. By knowing the exact times at the Greenwich meridian and at a ship's position, one could find longitude by calculating the time difference. However, most scientists, including Isaac Newton, discounted a clock because there were too many variables at sea. Changes in temperature, air pressure, humidity and gravity would surely render a watch inaccurate. Harrison persisted. As Dava Sobel writes, he worked on his timepiece for decades, though he suffered skepticism and ridicule. Even after completing his timepiece, an instrument we now call a chronometer, in 1759, he underwent a long series of unfair trials and demonstrations. Ultimately he triumphed. Sobel, a science writer who contributes to Audubon, Life, Omni and other magazines, captures John Harrison's extraordinary character: brilliant, persevering and heroic in the face of adversity. He is a man you won't forget.
Rating:
Summary: Great story, but BEWARE of inaccuracies in this book
Review: John Harrison completes his first pendulum clock in 1713 before the age of 20. He made the gears for this out of wood which was radical for such a use, but as a carpenter, perhaps not to him---which is a mark of genius, I'd say; to reach beyond accepted norms in this manner. This he did after borrowing a book on math and the laws of motion; which he copied word for word, making his own copy. He incorporated different varieties of wood into his clock for strenth and later invented a bi-metal pendulum to counteract the expansion and compression of various individual metals. He also employed friction-free movements so as to do away with problematic lubricants. When intrigued by the puzzle of time at sea and the issue of longitude he contemplated substituting something not prone to gravity, as a pendulum of course is, to track times passing. In 1737 he creates a cantilevered clock 4 foot square. The "Longitude board" (which had offered a cash bonus to anyone who could devise a method in which time at sea could be kept) admired this prototype. Four years later he returns with an improved model; then starts on a 3rd model, like the previous two, also a fairly large sized clock. But there exists a problem within this book: An artisan freemason by the name of John Jefferys at the Worshipful Company of clockmakers befriends Harrison and then later presents to him a pocket watch in 1753. Then in 1755, while still working on his 3rd model, Harrison says this to the Longitude board: I have..."good reason to think" on the basis of a watch "already executed that such small machines[he's referring to pocketwatches] may be of great service with respect to longitude." He then completes version 3 in 1759. His fourth version appears just a year later, however, and is a 5 inch wide pocketwatch! The obvious inference made by the author is that after he received the pocketwatch from Jeffreys he seemingly put his version #3 on the backburner and soon started on the pocketwatch 4th version. The author does not claim Harrison copied anything from the Jeffreys model, but she certainly phrases this section so as to lend one to believe that this may have been the case; that Jefferys had a hand in the masterstroke invention Harrison eventually produced in version #4. This is not true. Harrison commissioned the watch he received from Jeffreys and was based on Harrison's specifications. It seems that Harrison simply asked Jeffreys to test an idea which he himself hadn't the time to attack just then; as he was still working on his 3rd version of a table-top prototype clock. Hence Harrison's above statement to the board in 1755 whence his ideas were validated by Jeffreys. In addition, the author plays up the part of the Astronomer Royal's part in attempting to impede Harrison from convincing the longitiude board of the efficacy of a time-piece solution to this problem over a celestial answer to this conundrum. The author also jazzes up the issue of whether Harrison received the prize the board promised to pay for a successful solution herein; even though the board supported him for upwards of 20 years as he pursued this quest. It's as if the author intentionally omitted some facts (that the Jefferys was a Harrison commission), and pumped up others (of a rival/foil on the board trying to impede Harrison and the compensation issue; implying that Harrison was jipped) just to make the story more compelling. John Harrison's story, however, is extremely compelling as it is and didn't need this extra spice served up by the author.Do read this (very short) book on how this Mr. Harrison solved the problem of knowing where one is when at sea; and if you're in London, visit the Old Royal Observatory and the Clockmakers museum (in the Guildhall) where you can see Harrison's wonderful creations in person. Enjoy!
Rating: 
Summary: Slightly contradictory, but engaging and worthwhile
Review: Longitude bills itself as "the true story of a lone genius who solved the greatest scientific problem of his time," and in this sense the book delivers. Dava Sobel provides a fascinating account of the state of maritime transport back in the days when no one really knew where he was once he hit the open seas. Sure, anyone could figure out the ship's latitude by looking at the sky, but determining how far east or west one had sailed was another story entirely, and one that included many lethal shipwrecks.
Two 18th century camps emerged to solve the puzzle that offered a 20,000-pound prize. One, supporters of the so-called lunar distance technique, looked to the stars. The other, which included the book's hero, looked to building better clocks. Guess which camp won?
Therein lies one of the books contradictions. Sobel gives due credit to John Harrison for being the first to solve the puzzle by building the world's first seaworthy precision timepiece. Harrison had a gift for seeing what others could not and for turning his vision into durable, seaworthy non-pendulum clocks. (Just try using a pendulum clock at sea and see how long it keeps time.) Learning Harrison's history and his contributions is fascinating reading. But if Harrison solved the longitude problem in the mid to late 18th century and became so widely recognized, why then does Sobel say that the lunar distance proponents produced an almanac and tables from 1766 all the way though to 1907 that "everyone agreed...provided the surest way for mariners to fix their positions at sea"?
Sobel's style is very accessible to the novice. The book is a quick read and packs a lot of interesting information into its 175 pages, although I wish I would have leaned more about Harrison's breakthrough clock called the H-3. I recommend Longitude to all audiences and will turn to another Sobel work, Galileo's Daughter, with anticipation.
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