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    Re: Finding longitude in the 12th century
    From: John Huth
    Date: 2012 Sep 1, 08:02 -0400
    In the 12th century, there were many prime meridians used, which was a problem.   The polymath al-Biruni warned students of geography to be wary of the different choices.   He said that the westernmost point of Africa was typically used, but also the Cape Verde Islands appear to have been used.   This is more or less in keeping with Ptolemy's concept of an 'ocumene' or occupied hemisphere.

    As far as longitude was concerned, in the 12 century, the tables tables invariably got longitude from dead reckoning reports of travelers.   There may have been one or two experiments with eclipses, but the longitudes weren't good to much better than 6 degrees when you look over very long distances (e.g Africa through trade routes in Asia).

    On Sat, Sep 1, 2012 at 2:16 AM, Gary LaPook <garylapook@pacbell.net> wrote:
    Try here:





    --- On Fri, 8/31/12, Luther Abel <luabel@ymail.com> wrote:

    From: Luther Abel <luabel@ymail.com>

    Subject: [NavList] Re: Finding longitude in the 12th century
    To: "NavList@fer3.com" <NavList@fer3.com>
    Date: Friday, August 31, 2012, 10:47 PM

    Ah, but then where did those log trig tables come from?

    BTW, in the 1930s, the word computer" described someone who computed with a comptometer. 

    Sent from my iPhone

    On Aug 31, 2012, at 9:20 PM, Gary LaPook <garylapook@pacbell.net> wrote:

    I remember my father showing me a comptometer in his office in 1954. It could multiply and divide! It was amazing! It had all of these little windows showing numbers and it whirred for a while. seehttp://upload.wikimedia.org/wikipedia/commons/thumb/e/ee/Comptometer_Model_WM.jpg/220px-Comptometer_Model_WM.jpg

    I believe that the calculations for HO 214 where done using LOG TRIG tables and the comptometers were used for adding and subtracting the logs since you don't have to multiply or divide logs for navigation calculation (but for exponentiation and finding roots, you do.)


    --- On Fri, 8/31/12, Lu Abel <luabel@ymail.com> wrote:

    From: Lu Abel <luabel@ymail.com>
    Subject: [NavList] Re: Finding longitude in the 12th century
    To: "NavList@fer3.com" <NavList@fer3.com>
    Date: Friday, August 31, 2012, 10:19 AM

    While computers were far in the future, these WPA workers at least had comptometers, desktop mechanical calculators.  Would somebody in medieval times devote ten times as much effort doing it with pen on parchment?   

    In fact, did they even have the math back then?  I don't know if successive approximation was used in calculating HO 214, but successive approximation requires calculus, which was invented by Issac Newton centuries later.  

    Oh, and let's remember that Europe was fragmented into tiny medieval kingdoms less likely to support scholarly study.  There was a net loss of knowledge from Roman times until scholarly activities were reignited during the Renaissance. 

    If anyone was likely to be able to calculate longitude back then it would have been the Arabs who kept scholarship and knowledge alive while Europe sank into the Dark Ages.  But did they have an interest in calculating longitude?

    On the other hand, if the issue were changed from "calculation of longitude" to "figuring out where specific constellations would be observed the way they're shown on this clue" then the premise of the novel might work.   I think we've had discussions on this list of everything from Polynesian navigation to the constellations and stars depicted in Van Gogh's "Starry starry night" where the issue of matching the appearance of constellations has come up.  

    Suggest the discussion be moved from astronomers to Dan Brown...

    From: Gary LaPook <garylapook@pacbell.net>
    To: NavList@fer3.com
    Sent: Friday, August 31, 2012 12:48 AM
    Subject: [NavList] Re: Finding longitude in the 12th century

    Tables of Computed Altitude and Azimuth, H.O. 214 were calculated by out of work mathematicians put to work by the WPA (Works Progress Administration) during the Great Depression and the first volume came out in 1936.


    --- On Thu, 8/30/12, Geoffrey Kolbe <geoffreykolbe@compuserve.com> wrote:

    From: Geoffrey Kolbe <geoffreykolbe@compuserve.com>
    Subject: [NavList] Finding longitude in the 12th century
    To: NavList@fer3.com
    Date: Thursday, August 30, 2012, 10:31 PM

    There is a thread running on the History of Astronomy forum (HASTRO) started by Janie Schwab (schwab@DUDLEYOBSERVATORY.ORG) who relayed a request by a movie script writer. The script concerns an island in the Med where a fantastic treasure is buried. The whereabouts of this island was historically lost, but an artifact with the island's latitude and longitude written on it is discovered in the present day. The heros correct the error in the lat. long. by using a depiction of Orion on the artifact.

    The discussion follows along the lines of finding the position of cities by the timing of lunar eclipses. But one contributer, Clyde Hostetter, says, "I spent some of WWII as a Navy officer, learning and using a system for determining a point's latitude and longitude using only sightings of stars. So did other navigators. The secret was volumes of WPA calculations which were used to convert the star sightings into an accurate-enough location that all Navy ships used...and will again use if the satellites all fail."

    Does anyone here have any comments on this WPA method (whatever that was)?

    Can anyone suggest a means of finding accurate longitude using methods available in the 12th century?

    Is there a way of using a depiction of Orion to correct for an error in longitude?



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