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    Re: Time sights
    From: Fred Hebard
    Date: 2005 Jun 1, 14:19 -0400

    Alex,
    
    Quite right, many of the things you said were correct, except for the
    main point.  They did send time pulses within a few days or weeks of
    getting the cable operational, or possibly even a few hours or minutes,
    with the objective of determining the difference in longitude, and were
    successful, as I recall.
    
    There's a very nice book on the laying of the cable, which profiles the
    New York business man who initiated and directed the operation from an
    administrative point of view.  He was lucky enough to engage the
    physicist David Thompson, later Lord Kelvin, as his chief scientist,
    and I believe they understood most of the electrical aspects of the
    operation and were prepared for them.  Thompson was onboard ship as the
    cable was being laid on at least one of the attempts, along with the
    administrator.  The name of the book may be "A Thread Across the Ocean:
    The Heroic Story of the Transatlantic Cable;" I don't have my copy at
    hand to check.
    
    Fred
    ------------------------------------------------------------------------
    Frederick V. Hebard, PhD                      Email: mailto:Fred{at}acf.org
    Staff Pathologist, Meadowview Research Farms  Web: http://www.acf.org
    American Chestnut Foundation                  Phone: (276) 944-4631
    14005 Glenbrook Ave.                          Fax: (276) 944-0934
    Meadowview, VA 24361
    On Jun 1, 2005, at 2:06 PM, Alexandre Eremenko wrote:
    
    > Fred,
    > What I wrote is not COMPLETELY incorrect:-)
    > The time spread of signals DID happen.
    > And the first short telegram sent DID take
    > several hours to transmit (I don't remembr, 6 or 12 hours,
    > but of this order of magnitude).
    > That they sooner or later found some way to overcome this
    > difficulty might be true. But I doubt they knew how to do it
    > at the time they layed the cable.
    > Alex.
    >
    > On Wed, 1 Jun 2005, Fred Hebard wrote:
    >
    >> Actually, this is completely incorrect.  One of the first things done
    >> with the first transatlantic cable was to transmit time signals to
    >> determine more accurately the difference in longitude between North
    >> America and Europe.  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.
    >>
    >> Fred
    >>
    >> On Jun 1, 2005, at 11:28 AM, Alexandre Eremenko wrote:
    >>
    >>> I can suggest another reason why time transmission though
    >>> a transatlantic (or other very long) cable could not be acceptable.
    >>> In those XIX century cables,
    >>> the signals were substantially spread in time
    >>> when transmitted.
    >>> For example, in the very first transatlantic cable,
    >>> a short message of few words had to be transmitted
    >>> for several hours. A sharp impuls you send from one end
    >>> arrived as a very long wave.
    >>> So reliable transmission of a time signal could be
    >>> impossible.
    >>> Alex.
    >>>
    >>>
    >>> On Wed, 1 Jun 2005, Fred Hebard wrote:
    >>>
    >>>> In reading the Wikipedia entry on celestial navigation, I came
    >>>> across
    >>>> the following statement:
    >>>>
    >>>> "Traditionally, a navigator set his chronometer from his sextant,
    >>>> at a
    >>>> geographic marker surveyed by a professional astronomer. This is
    >>>> now a
    >>>> rare skill, and most harbor masters cannot locate their harbor's
    >>>> marker."
    >>>>
    >>>> A few years ago, in discussing a late 19th-century book about repair
    >>>> of
    >>>> submarine telecommunications cables, I asked why the captain and
    >>>> first
    >>>> mate went ashore to do time sights, when the could have gotten time
    >>>> from the cable.  I suppose the answer was that time wasn't sent over
    >>>> the cable that often, not to mention that it might have been broken
    >>>> when they were in harbor.  At any rate, this is the first mention I
    >>>> have of people setting their chronometer from a precisely measured
    >>>> location.  Previously, I had gather from this list that the captain
    >>>> and
    >>>> first mate were rating their chronometer, not setting its absolute
    >>>> time.  It appears they were setting it, and perhaps also rating it.
    >>>>
    >>>> Is there any mention of this in the older texts, such as Chauvenet,
    >>>> where time sights were done at geographic markers set by a
    >>>> professional
    >>>> astronomer?
    >>>>
    >>>> Thanks,
    >>>>
    >>>> Fred
    >>>>
    >>>
    >>
    >
    
    
    

       
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