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    Re: Celestial position-finding on land
    From: Bob Goethe
    Date: 2016 May 3, 08:16 -0700

    Lewis and Clark were instructed in sextant use before their departure, but seem to never have grasped the importance of time, and managed to let their chronometer run down early in their trip.  They recorded most of their observations only in reference to local solar noon.  Hence, they ended up doing a good job of recording landmarks' latitude, but with no real idea of their longitude.  When they returned, mathematicians tried long and hard to wring some longitudinal information out of their raw data, but to no avail.

    I understand that Dr. Livingstone mapped southern and central Africa in the 1850s by sextant.  But I have not gone much further in researching that...and I recall reading that shortly after his time, telegraph lines were run hither and thither, accompanied by some fairly accurate surveying, and not much use was ever made of Livingstone's celestial observations.

    David Thompson, the man who surveyed much of Canada around 1800, was quite skilled in his celestial navigation, and created maps that were still used into the 20th century.  From the National Geographic, May 1996, "The Man Who Measured Canada", page 122:

    When Thompson was 18, he broke his leg and was left to heal at a remote Saskatchewan trading post.  There he met Philip Turnor, the HBC's premier surveyor, and voraciously absovbed mathematics and practical astronomy from the master.  He began a daily journal and never move another uncharted mile without fixing the position of key landmarks and trading posts, points that became the framework for his maps of North America.

    Thompson later carried a sextant and a set of charts and tables wherefver he went, more like a British sea captain than a trader.  Because he had no ocean, he used a small pan into which he poured mercury, creating an artificial horizon to reflect sun, moon, and stars.  In his kit were two thermometers, drawing instruments, and foolscap-size paper.

    To his companions Thompson seemed a magician.  They often saw him gazing for hours into the skies and called hijm Koo Koo Sint - the Man Who Looks at Stars.  "I told them it was to determine the distance and direction from the place I observed to other places, but neither the Canadians nor the Indians believed me.  Their opinions were that I was lookng into futurity."

    Somebody named J. Gottfred seems to have researched Thompson's notes extensively, and recorded his results at http://www.northwestjournal.ca/dtnav.html.

    Bob

       
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