Marine chronometer, lunar distance method or something else altogether?

Trying to find a method to determine longitude at sea was one of the greatest technical problems of the Early Modern Period. Quite a wide-range of ideas were floated of which the most were either totally impractical or simply false. In the end the two main competitors were: on the one hand the attempts to develop a clock reliable enough to carry time from a given starting point accurately enough through all the vicissitudes of a long sea voyage to be then compared with local time and thus to determine longitude, i.e. the marine chronometer. Or on the other to develop accurate tables of the Moon’s orbit respective a set of given fixed stars in order to be able to use the Moon’s position at any given time as a clock with which to calculate longitude, i.e. the lunar distant method. Both of these concepts were first presented in the sixteenth century but it took until the middle of the eighteenth century before they could be realised.

Around 1760, Tobias Mayer succeeded in delivering up a set of tables of the lunar orbit accurate enough to be used for determining longitude using the lunar distance method. Shortly after this John Harrison showed with his H4 that a solution with a chronometer was also possible. Unfortunately even with the naval almanac produced by Nevil Maskelyne to simplify the calculations the lunar distant method was mathematically difficult to execute. As I have written elsewhere although Harrison’s H4 showed that a chronometer solution was possible, the clock itself was too complex and too expensive to provide a real solution to the longitude problem. It would take well into the nineteenth century before enough affordable, accurate chronometers were available to make this a viable mass method. Many sources claim that in the mean time navigators used the lunar distant method, but did they?

It would appear that for the first fifty or so years following those breakthroughs seafarers relied on a mixture of navigational methods to help determine their longitude. Principally they relied on the old tried and trusted method of dead reckoning. This is the process of calculating the ships new position from a previous one based on compass direction, ship’s speed based on log line measurements, and knowledge of currents. In the period we are talking about, many navigators checked their dead reckoning results against chronometer or lunar distant determinations. Given the lack of reliability of the available chronometers the navigators often carried several watches, comparing or even averaging the results. Sometimes the lunar distant method was only used by landfall to correct or control the longitude determined by dead reckoning. In general it seems that the well-established dead reckoning was the principle method used, supplement by one or other or both of the new methods, although neither of them was really trusted by the navigators.

For a more detailed picture of the navigational methods used from the middle of the eighteenth century to the middle of the nineteenth by the various European sea going nations I can recommend Navigational Enterprises in Europe and its Empires, 1730–1850 (1) edited by Richard Dunn (@Lordoflongitude) and Rebekah Higgitt (@beckyfh) a set of academic papers that supplement their more popular, excellent Finding Longitude.


After an excellent general introduction to the subject by the editors follow eleven papers covering a wide range of aspects of the subject, all of which maintain a very high level of scholarship.



My only real quibble with the book is the unfortunately usual high price putting it beyond my humble resources and probably those of most others interested in reading and learning from this highly informative volume.

(1) Ricard Dunn & Rebekah Higgitt eds., Navigational Enterprises in Europe and its Empires, 1730–1850, Palsgrave Macmillan, 2015


Filed under History of Navigation, Uncategorized

6 responses to “Marine chronometer, lunar distance method or something else altogether?

  1. The price is certainly steep (£63 on Amazon) and is presumably only expected to be sold to academic libraries. Given that there is probably a potential readership numbering at least one order of magnitude greater than the expected hardback sales I find the kindle price (£59.95) makes no sense. All you can say is “publishers” and leave it at that I suppose.

  2. jrkrideau

    I often want to read a book but not necessarily add it to my collection. I am a) cheap, and b) have limited bookshelf space. My local public library is remarkable good at hunting books down through its interlibrary loan service (at generally no cost)

    The most recent was Ruth Laudan’s Cuisine and Empire from the Brantford public library. Thanks for pointing me towards Ruth’s blog Thoney.

    In at least one case they tracked down a book for me in an academic library in another province about 1,100 km away.

    Do German public libraries offer the same service?

    • In Bavaria, where I live, because universities are paid for with tax payers’ money, every tax payer has the right to use university libraries; you just need to register, it costs €5. Through the local university library I have access to an extensive interlibrary loan system; in fact the book I reviewed above came through interlibrary loan.

      Although I have virtually no money to speak of I do buy books and possess a small but select #histSTM research library. I have a section on cartography, geodesy, surveying and navigation and Navigational Enterprises would fit in very nicely. I have bought more expensive books but this one is too marginal to justify the price.

      Up till now I have bought two copies of Rachel Laudan’s Cuisine and Empire, one for my sister and one for my step mother; we are all foodies! I might buy one sometime for my own history of food section.

  3. The longitude award triggered many foolish proposals to measure longitude on sea. One which is worth to go into the history of mankind and superstition is “the powder of sympathy” – method “invented” 1687 by a certain Sir Kenelm Digby: This powder (green vitriol, i.e. just dehydrataed iron sulphate) should heal wounds at a distance. The trick should be that the healing over distance would cause pain. Now the method for longitude measurement is obvious: Wound a poor dog (with a knife), take the dog on board of the ship sailing into the world, dip the dog’s bandage into a solution of the powder of sympathy every day at local noon in London – the dog would of course yelp immediately at the distance. The dog’s cry would directly deliver the time difference to London. Probably a disadvantage that on a major voyage one would have to injure the poor dog more than once.
    Einstein would have loved this method of time measurement and simultaneity!

    I learned this great physics from the book “The Illustrated Longitude” by Dava Sobel and William Andrews, Walker, New York.

    Don’t laugh about Sir Digby: Our belief in an afterlife is of a similar intellectual quality; the difference is that it is an inherited common belief.
    If it were a new information, you would probably smile, too.
    (Thony: You are of course free to delete this non-longitudinal remark).

  4. Speaking of Dava Sobel…

    I was put off reading her Longitude by the many negative remarks about it on this blog, but my book group recently read her The Glass Universe. (Selected by the librarian.) This is about the women working for the Harvard Observatory, under the direction of Edward Pickering, in the late 19th and early 20th century.

    Plusses: interesting to see the background and “infrastructure” behind such big 20 C. discoveries as the multitude of galaxies or the expansion of the universe or the theory of stellar evolution. Things like the creation of extensive spectrographic catalogs, and classification systems. Also, while I knew of the achievements of Henrietta Leavitt, Annie Cannon, and Cecilia Payne-Gaposchkin before reading this book, I knew almost nothing about their personal stories. I had also never realized how important Edward Pickering was to the history of astrophysics.

    Big minus, IMO: Sobel does bad job of explaining the science. Not so much inaccuracies, but it’s all puréed into the human interest, never told in a connected manner. Other book club members, even those more into the human interest than the astronomy, complained about it.

    • One of my acquaintances is Omar Nasim, professor for the history science at the University of Regensburg, who is doing serious research on the Harvard glass plates and in a conversation he said that he was underwhelmed by The Glass Universe.

      After Longitude and A More Perfect Heaven I don’t read Sobel’s books.

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