Welcome to the NavList Message Boards.


A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

Compose Your Message

Add Images & Files
    Name or NavList Code:
    Re: More on Thomas Hubbard Sumner
    From: Frank Reed CT
    Date: 2005 Feb 10, 23:19 EST
    George H wrote:
    "What surprises me, is that it took until 1837 for navigators to realise
    that a useful position line could be drawn from a single observation of the
    altitude of a body, even if it wasn't at meridian passage."
    You mentioned this before, and it's an interesting issue. My own take is that this resulted from the conceptual framework of an era that treated latitude and longitude as two entirely different matters both in principle and in practice, and also treated celestial observations as corrections to the dead reckoning. If you've got your head in that mindset, the very idea of determing a position from arbitary observations is almost unthinkable.
    Although 1837 is somewhat late, it's only about at this time that chronometers were becoming the rule aboard ship, and it's right around the dividing line that I described previously between "longitude by dead reckoning (occasionally checked by lunars)" and "longitude by chronometers+time sights (occasionally checked by lunars)". Once chronometers were ubiquitous, the fundamental equivalence of all celestial observations should have become more obvious. So maybe it's not so terribly late after all. Maybe more shocking is the fact that celestial lines of position were still considered "fancy navigation" even fifty years after Sumner's discovery. Why that delay? In some part, at least, because the academic "nautical astronomers" (Chauvenet comes to mind) were still so fascinated by lunars and "old" methods that they don't seem to have recognized the revolutionary significance of the line of position.
    One other bias from this early era: calculation was "in" and plotting was "out". There was a very strong bias towards methods that yielded the vessel's position by direct "exact" calculation with logarithms. Plotting a celestial line of position would have seemed alien and inexact when first proposed.
    42.0N 87.7W, or 41.4N 72.1W.
    Browse Files

    Drop Files


    What is NavList?

    Get a NavList ID Code

    (please, no nicknames or handles)
    Do you want to receive all group messages by email?
    Yes No

    A NavList ID Code guarantees your identity in NavList posts and allows faster posting of messages.

    Retrieve a NavList ID Code

    Enter the email address associated with your NavList messages. Your NavList code will be emailed to you immediately.

    Email Settings

    NavList ID Code:

    Custom Index

    Start date: (yyyymm dd)
    End date: (yyyymm dd)

    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site