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
    Re: Time sights
    From: Paul Hirose
    Date: 2005 Jun 1, 20:22 -0700

    Fred Hebard wrote:
    > There are ways of transmitting signals both ways
    > to account for the various delays.  Paul Hirose was kind enough to tell
    > us how this was done a few years ago; unfortunately, I didn't
    > understand the mechanism well enough to reproduce it here.
    I probably explained it badly. To illustrate the principle, suppose
    the clocks at either end of the line are in perfect synchronism. If I
    tap my telegraph key precisely at the top of a minute (according to my
    clock), your telegraph sounder clicks, say, 0.1 s later. From your
    viewpoint, your clock is 0.1 s *ahead* of mine.
    But if we exchange roles, I hear your ticks coming late by
    0.1 s. From my viewpoint, your clock is 0.1 s *behind* mine. By taking
    the mean of these results, the delay is cancelled and
    the true time offset determined. As a byproduct, the discrepancy between
    the two measurements, divided by two, equals the propagation delay.
    In practice, break-circuit clocks automatically generated the seconds
    pulses, which were recorded as helical ink traces on paper by rotating-drum
    chronographs. The equipment and techniques were developed with amazing
    rapidity. By the time of this report in 1858, telegraphic longitudes
    were routine:
    The great length of the trans-Atantic cable did create technical
    challenges, but they were were quickly overcome:
    ("A Cardinal Point for Longitude")
    According to footnote 26 at the bottom of that page, "The seconds in
    time of longitude of the Cambridge Observatory [i.e., the seconds
    portion of the Harvard College observatory time offset with respect to
    Greenwich] as determined with the 1927 North American Datum was 30.928
    and as determined in the 1983 North American Datum was 30.802. The
    original telegraphic determination of longitude fell approximately
    half-way between these values demonstrating beyond a doubt the accuracy
    of the 'American Method' of longitude determination."
    I recommend science writer Trudy Bell's article on telegraphic
    longitude, "The Victorian Global Positioning System" (about 840 k PDF):

    Browse Files

    Drop Files


    What is NavList?

    Join NavList

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

    You can also join by posting. Your first on-topic post automatically makes you a member.

    Posting Code

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

    Email Settings

    Posting 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