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    Re: Margett's Tables/graphical longitude.
    From: Ken Muldrew
    Date: 2016 Jan 13, 19:58 -0700

    On 2016-01-13, at 5:29 AM, Francis Upchurch wrote:

    Thanks also to Ken Muldrew who likewise made me aware of this "gem" as he calls it and see Ken's post of 26th April 2006 for an interesting technical description of how it was likely created originally back in 1790. Any more news or update on this Ken? 

    Hi Francis,

    That initial speculation on how the tables were created was completely wrong. Margetts simply (simply!) plotted the data from the Cambridge Tables, an enormous book (about 1100 pages) of cleared lunar distances that was produced in 1772 by Israel Lyons and a team of computers (humans who did numerical calculations). He effectively made the Cambridge Tables available to sailors as an 1100 page tome was a bit much just to save the navigator from doing a few calculations. Unfortunately, analytic geometry and graphical methods were not well known among non-mathematicians of the time so Margetts' book never found the wide distribution that it deserved.

    Ken Muldrew.


       
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