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    Re: Time sights
    From: Fred Hebard
    Date: 2005 Jun 1, 13:37 -0400

    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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