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    Re: Lunars in history
    From: Tom Harnish
    Date: 2021 Jul 5, 11:02 -0700

    I was surprised by the stones you threw at Murchie, Frank, saying that the method didn't require the skill of a magician as Murchie claimed, that lunars were commonly used by common navigatorsand that he was wrong to attribute the lunar method to Newton.

    So I decided to rummage around and see what I could find out about lunars. As a backyard astronomer and as a sailor the topic sounded interesting and I was curious why Murchie, who taught and practiced navigation for years, could be so wrong. I'm glad you brought it up as it turned out to be a very interesting topic, indeed.

    But now I'm really confused.

    I stumbled on an old article by Littlehales who wrote, "At sea the observation of a lunar distance requires great accuracy and skill, especially if there be much vibration in the vessel; and it is found that hardly one navigator in two hundred has ever carried out the calculation of a longitude by the lunar-distance method in practice." Then I discovered Lecky and Allingham who famously wrote lunars were, by about 1850, "deader than Julius Caesar" and Leaky himself who's quoted as saying, "... [t]he writer of these pages, during a long experience at sea in all manner of vessels [since the 1850s] ..., has not fallen in with a dozen men who had themselves taken Lunars, or even had seen them taken."

    I think you can see why I'm confused when you say the method was a common practice.

    I'm also confused by why you discount Newton's association. Granted Werner and others considered the idea in the late Middle Ages, but they didn't have sufficiently precise celestial ephemerides to actually use the method. In any case, it wasn't until the early 1700s when Dunthorne produced his version of ephemeris tables, "...exactly constructed from Sir Issac Newton's Theory..." that a simplified way of clearing lunar distances existed. The helpful Stark Tables didn't exist in the 40s and the Nautical Almanac stopped publishing lunar distance tables in the early 1900s so trying to use the method in the '40s would seem to require some kind of potent magic, just as Murchie suggests.

    But I certainly could be wrong about all this, and your opinion of Murchie doesn't make lunars any less interesting as a method of telling time and longitude.

    I'm eager to learn more, so if you can point me to some other sources that will clear up my confusion I'll be very grateful.

       
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